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Arsenic exposure and type 2 diabetes: a systematic review of the experimental and epidemiologic evidence.

Chronic arsenic exposure has been suggested to contribute to diabetes development. We performed a systematic review of the experimental and epidemiologic evidence on the association of arsenic and type 2 diabetes. We identified 19 in vitro studies of arsenic and glucose metabolism. Five studies reported that arsenic interfered with transcription factors involved in insulin-related gene expression: upstream factor 1 in pancreatic [beta]-cells and peroxisome proliferative-activated receptor [gamma] in preadipocytes. Other in vitro studies assessed the effect of arsenic on glucose uptake, typically using very high concentrations of arsenite or arsenate. These studies provide limited insight on potential mechanisms. We identified 10 in vivo studies in animals. These studies showed inconsistent effects of arsenic on glucose metabolism. Finally, we identified 19 epidemiologic studies (6 in high-arsenic areas in Taiwan and Bangladesh, 9 in occupational populations, and 4 in other populations). In studies from Taiwan and Bangladesh, the pooled relative risk estimate for diabetes comparing extreme arsenic exposure categories was 2.52 (95% confidence interval, 1.69-3.75), although methodologic problems limit the interpretation of the association. The evidence from occupational studies and from general populations other than Taiwan or Bangladesh was inconsistent. In summary, the current available evidence is inadequate to establish a causal role of arsenic in diabetes. Because arsenic exposure is widespread and diabetes prevalence is reaching epidemic proportions, experimental studies using arsenic concentrations relevant to human exposure and prospective epidemiologic studies measuring arsenic biomarkers and appropriately assessing diabetes should be a research priority. Key words: arsenic, diabetes, glucose metabolism, meta-analysis, systematic review.

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Type 2 diabetes mellitus is a metabolic disorder characterized by hyperglycemia, insulin resistance in peripheral tissues, and altered insulin secretory capacity of pancreatic [beta]-cells. Type 2 diabetes accounts for 90-95% of all cases of diabetes and is a major public health problem worldwide (Wild et al. 2004). Established risks factors of type 2 diabetes include older age, obesity, physical inactivity, family history, and genetic polymorphisms. In addition, environmental toxicants, including arsenic, have been suggested to play an etiologic role in diabetes development (Longnecker and Daniels 2001).

Arsenic is a recognized toxicant and carcinogen. Nonoccupational exposure occurs mainly through drinking water, affecting millions of people worldwide. Exposure to levels of arsenic in drinking water well above 100 ppb has been associated with an increased risk of type 2 diabetes in the high-arsenic areas of Taiwan and Bangladesh (Lai et al. 1994; Rahman et al. 1998). The biological mechanisms for an association between chronic arsenic exposure and increased diabetes risk are not known [National Research Council (NRC) 1999, 2001; Tseng 2004].

Previous reviews of the role of arsenic in diabetes have questioned the quality of the evidence but were supportive of the possibility of an association [NRC 1999, 2001; Ng 2001; Tseng 2004; Tseng et al. 2000, 2002; World Health Organization (WHO) 2001]. These reviews, however, did not use systematic review criteria and may be subject to biased selection of the evidence. Our objective was to perform a systematic review of the experimental and epidemiologic evidence on arsenic and type 2 diabetes. We examined experimental studies (in vitro or in vivo) to synthesize available information on plausible mechanisms for the effect of arsenic on glucose metabolism, as well as epidemiologic studies to synthesize the association of arsenic exposure with diabetes risk in humans.

Materials and Methods

Search strategy and study selection. We searched the Medline database (http:// www.ncbi.nlm.nih.gov/entrez/query. fcgi?db=PubMed) and the TOXNET database [consisting of TOXLINE, GENETOX, and DART/ETIC (Developmental and Reproductive Toxicology/Environmental Teratogen Information Center); http:// toxnet.nlm.nih.gov/] from 1966 through July 2005 using free text and the medical subject headings (MESH) arsenic, arsenite, arsenate, arsenicals, diabetes, glucose, glycosylated hemoglobin, insulin, and mortality. In addition, we manually reviewed the reference lists from relevant original research and review articles.

For experimental studies, we identified in vitro or in vivo studies of the administration of arsenic or arsenic compounds, including inorganic arsenite (trivalent arsenic), inorganic arsenate (pentavalent arsenic), and others, and outcomes related to diabetes status or glucose and insulin metabolism. For epidemiologic studies, we identified studies assessing arsenic exposure through measures of environmental samples, biomarkers, or indirect measures (e.g., job titles reflecting occupational exposure or living in areas with known exposure via drinking water) and diabetes status or markers of glucose metabolism.

The exclusion criteria for experimental and epidemiologic studies were a) no original research (reviews, editorials, nonresearch letters); b) studies performed only on people with diabetes, including case reports; c) lack of outcomes related to diabetes or glucose metabolism; d) no data on arsenic exposure; e) experiments in nonmammalian cells, or noncellular experiments; f) animal studies administering a single dose of arsenic; and g) culture cell experiments using lewisite or oxophenylarsine. Figure 1 summarizes the study selection process.

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Two investigators (A.N.-A., R.A.S.) independently abstracted the articles that met the selection criteria. Discrepancies were resolved by consensus. We converted all arsenic concentrations to parts per million or parts per billion, including concentrations from in vitro studies, which were usually reported in molar units of arsenic (1 [micro]M of arsenic = 74.9 [micro]g/L = 74.9 ppb).

Statistical methods. Measures of association in epidemiologic studies (odds ratios, prevalence ratios, standardized mortality ratios, relative risks, relative hazards, comparisons of means) and their SE values were abstracted or derived using data reported in the articles (Greenland 1987). Within each study, we used the model adjusted for the most covariates. Adjustment did not substantially modify the conclusions of any individual study. For five studies, we used data available in the original articles to derive relative risk estimates. For one study (Lagerkvist and Zetterlund 1994), because there were no cases among the unexposed, we added 0.5 to each cell to estimate the relative risk and the 95% confidence interval (CI). For Jensen and Hansen (1998), we compared the proportion of subjects with glycosylated hemoglobin above 7% across occupational exposure categories. For Ward and Pim (1984) and Ruiz-Navarro et al. (1998), we used the linear discriminant function method to estimate relative risks from comparisons of means (Greenland 1987). Finally, for Lewis et al. (1999), we estimated the relative risk of diabetes mortality comparing the highest with the lowest category of exposure within the cohort from the published standardized mortality ratios.

We grouped the studies in three categories: studies in general populations exposed to high arsenic levels, corresponding to studies in Taiwan and Bangladesh with average levels in drinking water well above 100 ppb; studies in occupational populations exposed to high arsenic levels most commonly in ambient air; and studies in general populations exposed to low or moderate levels of arsenic in drinking water (< 100 ppb), food, or ambient air. Because of substantial heterogeneity and methodologic limitations, we present a qualitative systematic review, and we used only meta-analysis techniques for studies from Taiwan and Bangladesh. For descriptive purposes, we report the range and the unweighted medians of the relative risk of diabetes comparing extreme categories of arsenic exposure in each study.

Results

In Vitro Experimental Studies

Nineteen in vitro studies published between 1965 and 2004 met our inclusion criteria (Figure 1, Table 1). None of the experimental studies were conducted in human cell lines. Five experiments investigated the effect of arsenic on insulin signal transduction and gene expression. Three studies were performed in transfected mouse pancreatic [beta]-cells, where exposure to high arsenite concentrations was similar to high glucose in stimulating insulin upstream factor 1 (IUF-1) (Macfarlane et al. 1997) and in stimulating the translocation of IUF-1 from the cytoplasm to the nucleus (Elrick and Docherty 2001; Macfarlane et al. 1999). IUF-1, also called homeodomain transcription factor PDX1, is a transcription factor that binds to the human insulin gene promoter and increases insulin messenger RNA levels in response to glucose. The effect of high glucose or arsenite was prevented by SB 203580, a specific inhibitor of stress-activated protein kinase-2 (SAPK2)/p38, whereas the effect of high glucose but not of arsenite was prevented by substances that specifically inactivate phosphatidylinositol-3 kinase (wortmannin and LY294002). Two other studies (Salazard et al. 2004; Wauson et al. 2002) investigated the role of arsenite in adipocyte differentiation and peroxisome proliferative-activated receptor [gamma] (PPAR[gamma]) expression. PPAR[gamma] is a transcription factor that regulates key gene expression for insulin sensitivity. These two experiments used different concentrations and lengths of exposure and produced opposite results. In the study by Salazard et al. (2004), the incubation of 3T3-F442A preadipocytes with 1.7 and 3 ppb (0.25 and 0.5 [micro]M) arsenite for 3 days induced the expression of PPAR[gamma] and CCAAT/ enhancer binding protein. In study by Wauson et al. (2002), the incubation of C3H 101T1/2 cells with 450 ppb (6 [micro]M) arsenite for 2 months prevented adipocyte differentiation through the inhibition of the PPAR[gamma]. Arsenite also inhibited the differentiating effect induced by pioglitazone, a PPAR[gamma] agonist used to reduce insulin resistance.

The rest of the in vitro studies assessed the effect of arsenic on glucose uptake, typically using very high concentrations of arsenite as general inducers of cellular stress. Ten studies measured basal glucose uptake (in the absence of insulin) in cell lines exposed to arsenite or other compounds (Table 1, Figure 2). Four of the studies also exposed the cells simultaneously to insulin and arsenite (Table 2). Compared with insulin alone, simultaneous exposure to insulin and arsenite decreased glucose uptake in insulin-sensitive cells (Bazuine et al. 2003; Walton et al. 2004). One of the studies (Walton et al. 2004) measured basal and insulin-stimulated glucose uptake in cells exposed to arsenate and to methylated arsenic compounds. Methylarsine oxide ([MAs.sup.III]O) inhibited insulin-stimulated glucose uptake at the concentration of 75 ppb after 4- or 24-hr exposure (Walton et al. 2004). For arsenite, because the concentrations used in glucose uptake studies were extremely high, their relevance to diabetes development in humans is questionable.

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Overall, in vitro studies provided limited insight into potential mechanisms that may explain an etiologic role of arsenic on diabetes.

In Vivo Experimental Studies

Ten experimental studies in mice, rats, goats, and guinea pigs published between 1979 and 2004 met our inclusion criteria (Figure 1, Table 3). Arsenite was evaluated in 6 studies (Biswas et al. 2000; Cobo and Castineira 1997; Ghafghazi et al. 1980; Pal and Chatterjee 2004a, 2004b, 2005), and arsenate in 2 studies (Aguilar et al. 1997; Hughes and Thompson 1996). Other compounds were methanearsonate (Judd 1979) and monomethylarsenic (Arnold et al. 2003). Six studies administered arsenic in water or food for lengths of time ranging from 4 weeks to 2 years, and 5 studies involved intraperitoneal exposure to arsenic for 5-30 days. The doses of arsenic were high or very high in most studies, with a lowest dose of 5.55 ppm arsenite (Pal and Chatterjee 2004a) and 0.025 ppm arsenate (Hughes and Thompson 1996).

Although all studies measured glucose levels in blood, plasma, or serum, only one study provided information on potential mechanisms (Cobo and Castineira 1997). In this study, the oral administration of arsenite did not affect insulin levels in vivo. However, a glucose stimulus applied ex vivo produced greater insulin release from the isolated pancreas cells of rats treated with arsenite in vivo compared with the insulin release from isolated pancreas cells of control rats.

Epidemiologic Studies

Study characteristics. Nineteen epidemiologic studies met our inclusion criteria (Figure 1, Table 4). Three studies were published between 1980 and 1984 (Enterline and Marsh 1982; Mabuchi et al. 1980; Ward and Pim 1984), and the other 15 were reported between 1994 and 2004. Only 2 studies used a prospective cohort design (Lewis et al. 1999; Wang et al. 2003). The rest used cross-sectional, case-control, or retrospective cohort designs. Two studies used the WHO diabetes definition based on oral glucose tolerance tests and/or self-reported medication to define diabetes, whereas the other studies used death certificates, medical or insurance records, urine tests for glucosuria, self-reported diabetes symptoms such as polyuria confirmed by two positive urine tests and a positive oral glucose tolerance test, glycosylated hemoglobin, or self-reported diagnosis. Two studies did not specify the diagnostic criteria. The number of diabetes cases ranged from 2 (Mabuchi et al. 1980) to 27,543 (Wang et al. 2003), but most studies had fewer than 100 cases. Studies in general populations included adult men and women, whereas occupational studies included mostly men.

There were substantial differences in arsenic exposure ascertainment. Most studies in general populations assessed exposure indirectly, using measurements of total arsenic levels in community drinking water sources. Two studies from Taiwan (Lai et al. 1994; Tseng et al. 2000), one from Bangladesh (Rahman et al. 1999), and one from the United States (Lewis et al. 1999) estimated a cumulative arsenic exposure index (ppm-year) by multiplying the number of years that individuals lived in a specific village/area by the average arsenic level in drinking water in that village/area (usually, in each area, several measurements were performed once in time). Other studies in Taiwan and Bangladesh assigned exposure on the basis of residence in an area determined to be endemic for arseniasis (Rahman et al. 1998; Tsai et al. 1999; Wang et al. 2003). None of the studies from Taiwan or Bangladesh obtained individual measures of arsenic exposure either from household tap water measures or more directly by using biomarkers of exposure. None of these studies assessed potential sources of exposure other than drinking water.

In occupational studies, exposure was based on job tide or on estimated arsenic levels in air for different job categories as assessed by a safety engineer (Rahman and Axelson 1995). One study in an occupationally exposed area assessed arsenic exposure based on years of residence within 4 km of a copper smelter during childhood (Tollestrup et al. 2003). Some occupational studies (Enterline and Marsh 1982; Jensen and Hansen 1998; Lagerkvist and Zetterlund 1994; Lubin et al. 2000) also measured arsenic in urine or air to confirm exposure, but this information was not linked to diabetes in the analyses. Only two studies used biomarkers of exposure: Ward and Pim (1984) measured total arsenic in plasma, and Ruiz-Navarro et al. (1998) measured total arsenic in urine, without speciation of inorganic and methylated compounds.

Quality assessment. In the epidemiologic studies we abstracted information to evaluate study quality, adapting the criteria proposed for observational studies by Longnecker et al. (1988). As shown in Table 5, most studies failed to fulfill important quality criteria such as individual measures of arsenic exposure using biomarkers, standard criteria to diagnose diabetes, or information on established risk factors for diabetes.

Relative risk estimates. The relative risk estimates comparing the highest with the lowest arsenic exposure categories are shown in Table 4. Studies in Taiwan and Bangladesh consistently identified an increased risk of diabetes with increased arsenic exposure, with relative risks ranging from 1.46 to 10.1 (median, 2.40) and with a pooled relative risk estimate using and inverse variance weighted random-effects model of 2.52 (95% CI, 1.69-3.75; p heterogeneity < 0.001). Occupational studies were small and showed no consistent pattern, with relative risks ranging from 0.34 to 9.61 (median, 1.40). We identified only 4 studies in general populations from countries with low or moderate arsenic exposure. These studies were small and did not show an increased risk of diabetes with increasing arsenic levels (relative risks ranged from 0.65 to 1.09; median, 0.95).

Five studies provided information on the dose response in diabetes risk by cumulative arsenic exposure in drinking water (Figure 3). Diabetes risk tended to increase with increasing cumulative exposure in studies from Taiwan (Lai et al. 1994; Tseng et al. 2000) and Bangladesh (Rahman et al. 1999). No trend was observed in the U.S. studies (Lewis et al. 1999; Zierold et al. 2004).

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Discussion

Summary of findings. The evidence on the association of arsenic exposure with diabetes risk summarized in this systematic review is inconclusive. Evidence from in vitro studies suggests that arsenic interferes with signal transduction and transcription factors that are related to insulin pathways such as IUF-1 in pancreatic cells or PPAR[gamma] in preadipocytes. In vitro glucose uptake experiments and in vivo studies did not provide evidence on potential mechanisms that may explain a diabetogenic effect of arsenic. In general, experimental studies were limited by the use of arsenic concentrations that were much higher than those relevant to human exposure. For example, the current U.S. Environmental Protection Agency recommended standard for arsenic in drinking water is 10 ppb. The lowest concentration of arsenite used in studies of cultured cells investigating glucose uptake was 750 ppb (Bazuine et al. 2003), and the lowest concentration of arsenite in animal studies was 5,550 ppb (Pal and Chatterjee 2004a, 2004b).

In epidemiologic studies, the association between arsenic exposure and diabetes across different populations and different sources of exposure was inconsistent. In populations exposed to high arsenic levels via drinking water in Taiwan and Bangladesh, diabetes risk was consistently increased. In occupational settings, diabetes mortality was increased in some studies and decreased in others. Finally, no association with diabetes was observed in four studies of general populations outside of Taiwan or Bangladesh. Overall, the quality of the epidemiologic evidence was limited by methodologic problems, particularly in assessing arsenic exposure and diabetes outcomes.

Mechanisms for arsenic-related diabetes. Acute arsenite toxicity, including its effects on glucose metabolism, is generally attributed to its reactivity toward thiol (SH) groups (Aposhian 1989; NRC 1999). During acute poisoning, arsenite inhibits pyruvate and [alpha]-ketoglutarate dehydrogenases (Aposhian 1989), essential enzymes for gluconeogenesis and glucolysis. The interference of arsenic with pyruvic acid metabolism was described by Krebs in the early 1930s (Krebs 1933). Arsenate, on the other hand, can replace phosphate in energy transfer pathways of phosphorylation and also uncouples oxidative phosphorylation (Kennedy and Lehninger

1949). However, these toxic effects of acute arsenic exposure are unlikely to occur as a result of chronic exposure to environmentally relevant doses (Tseng 2004).

The influence of arsenic on the expression of gene transcription factors may be related to diabetes risk. However, the effects of arsenite on IUF-1 and PPAR[gamma] were contradictory in terms of diabetes development. The differential effects may reflect a complex dose-response pattern for arsenic or differences in length of exposure to arsenic across studies. Further studies with wide ranges and durations of arsenic exposure are needed to investigate the effect of arsenic on these and other insulin-related events at the cellular and molecular levels. For instance, interference with the glucocorticoid receptor is another potential mechanism for arsenic-related diabetes that deserves further investigation. Arsenic shows a complex dose-response effect on glucocorticoid receptor mediated transcription (Bodwell et al. 2004), with a stimulatory effect at very low concentrations (6-120 ppb) and an inhibitory effect at doses greater than 120 ppb. The glucocorticoid receptor is a member of the steroid receptor superfamily that among other metabolic processes regulates gluconeogenesis. Reduction of glucocorticoid receptor expression in hepatic and adipose tissue has been shown to improve hyperglycemia in diabetic rodents (Watts et al. 2005).

Experimental studies on glucose uptake showed that arsenite increases uptake independently of the earlier steps of the insulin transduction pathway, although when co-administered with insulin, arsenite inhibited insulin-stimulated glucose uptake in 3T3-L1 adipocytes. The purpose of most of these studies was to investigate the role of stress in glucose uptake, which is unrelated to the possibility that arsenic could affect diabetes risk. Under these designs, cultured cells were exposed to high arsenic levels for a few hours, whereas humans are chronically exposed to lower concentrations. Only one study investigated methylated arsenical compounds and their interference in insulin signaling in adipocytes (Walton et al. 2004). For these reasons, the relevance of in vitro glucose uptake findings to diabetes etiology is uncertain.

Arsenic could influence diabetes development by other mechanisms, including oxidative stress, inflammation, or apoptosis, nonspecific mechanisms that have been implicated in the pathogenesis of type 2 diabetes. Arsenic exposure can enhance the production of reactive oxygen species (Barchowsky et al. 1999; Chen et al. 1998; Tseng 2004; Wang et al. 1996), interfere with the activity of key antioxidant enzymes such as glutathione reductase, glutathione S-transferase, glutathione peroxidase, and glucose 6-phosphate dehydrogenase (Maiti and Chatterjee 2000; Santra et al. 2000), and induce lipid peroxidation (Santra et al. 2000). In individuals from Taiwan, increasing blood levels of arsenic correlated with increasing levels of reactive oxygen species and with decreasing levels of antioxidant capacity in plasma (Wu et al. 2001). Arsenic may also up-regulate interleukin-6 and other inflammatory cytokines (Wu et al. 2003), and it may induce the release of tumor necrosis factor-[alpha] from mononuclear cells (Yu et al. 2002). Finally, arsenic is well known for inducing apoptosis in multiple cell lines (Waalkes et al. 2000). Future research should evaluate whether these mechanisms mediate the role of arsenic in diabetes development.

The in vivo experimental studies were mostly uninformative. The diversity of species studied probably reflects that there are no good animal models to study the effects of arsenic on diabetes development. Indeed, the classification of arsenic as a human carcinogen, although recently supported by animal models (Waalkes et al. 2004), was for a long time based on human data. Progress in the study of the role of arsenic in diabetes requires the identification of appropriate animal models.

Arsenic and diabetes in human studies. Suggestive evidence links chronic exposure to high arsenic levels in drinking water with increased diabetes risk in Taiwan and Bangladesh. Methodologic problems, however, limit the causal interpretation of this association. The use of average drinking water and the lack of individual measures of arsenic make it possible to underestimate exposure due to between-subject variability in water consumption and to other sources of arsenic exposure in these areas, such as contaminated food and cooking water. On the other hand, because arsenic exposure was assessed at the village level and diabetes diagnosis was often not performed according to standard procedures, this ecologic association could reflect the uncertain comparability of exposure groups in terms of socioeconomic development, access to care, study selection factors and other diabetes risk factors. The use of urine tests and of administrative data to identify diabetes makes it likely that only severe or symptomatic cases were identified, and it is uncertain whether the procedures and frequency for diabetes testing were similar across areas with different arsenic exposure. In addition, the use of administrative data can be affected by surveillance and diagnostic biases. For example in Taiwan, arsenic-related health problems in the endemic areas are well known, hence, subjects in these areas may have received different medical care, including different diagnostic services, compared with subjects in areas with lower arsenic levels.

It is also possible that the findings from Taiwan and Bangladesh may not be generalizable to other populations. Some reasons for this include variations in the distribution of polymorphisms in genes involved in arsenic metabolism or response (Loffredo et al. 2003), differences in arsenic species to which populations were exposed (Chen et al. 1995), other co-exposures (Chen et al. 1995), and dietary deficiencies that may interact with arsenic. For example, selenium and zinc levels in Taiwan and Bangladesh are among the lowest worldwide (Lin and Yang 1988), and poor dietary selenium has been suggested as an underlying factor for arsenic and cancer in Bangladesh and West Bengal in India (Spallholz et al. 2004). In guinea pigs, selenium and arsenic counteract each other in glucose metabolism (Das et al. 1989), and the joint effect of high arsenic and low selenium could play a role in diabetes development. Exposure to arsenic, selenium, other nutrients, and other diabetes risk factors were not measured in epidemiologic studies.

We found no reports of diabetes in populations known to be exposed to high levels of arsenic in drinking water in Chile and Argentina. This lack of information on diabetes could reflect a lack of research, but it has also been suggested to be related to publication bias (Longnecker and Daniels 2001).

The evidence from general populations outside of Taiwan or Bangladesh was inconclusive because of the small number of cases, limitations in study design, and misclassification of diabetes status. Occupational studies, on the other hand, could not be interpreted in favor or against an association because of uncertain comparability of study participants with the general population used as reference, limitations in exposure assessment, lack of information on concomitant exposures, lack of information on major diabetes risk factors, and the possibility of a healthy worker survivor effect.

An important conclusion we derived from the epidemiologic review is the limited quality of the evidence base. This finding is consistent with previous reviews, including those by U.S. and international panels (NRC 1999, 2001; Ng 2001; WHO 2001). These panels determined that the available evidence on arsenic and diabetes suffered from uncertainties in study design and exposure assessment. Our review further refines these reports and identifies the lack of biomarker data and the lack of standard criteria for diabetes assessment as major limitations of the evidence base. Current uncertainties in the role of arsenic in diabetes development could be reduced by conducting carefully planned epidemiologic studies in populations exposed to a wide range of arsenic levels. Future studies should a) measure appropriate arsenic biomarkers that integrate all sources of exposure (e.g., urine or toenails); b) carefully collect information on current and past sources of arsenic exposure and on potential confounders and modifiers, including known determinants of diabetes development; c) and prospectively ascertain diabetes using standard definitions.

Conclusion

The possibility of an association between chronic arsenic exposure and diabetes has implications for research and public health. Millions of people are exposed worldwide to moderate or high levels of arsenic in drinking water. Because diabetes is also a major public health problem, the public health consequences of a causal association could be serious. Methodologic problems limit the causal interpretation of the moderately strong association between high arsenic exposure and diabetes in Taiwan and Bangladesh. Overall, the experimental and epidemiologic evidence is at present insufficient and inadequate to establish causality. Experimental studies that use arsenic concentrations relevant to human exposures, and high-quality prospective epidemiologic studies that use appropriate methods for exposure assessment as well as rigorous criteria for outcome definitions should be research priorities.

CORRECTION

Table 1 has been modified from the original manuscript published online. The table now includes information on the 24-hr study by Walton et al. (2004).

Received 1 August 2005; accepted 15 December 2005.

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Ana Navas-Acien, (1,2,3,4) Ellen K. Silbergeld, (4) Robin A. Streeter, (1,3) Jeanne M. Clark, (1,2,5) Thomas A. Burke, (3,6) and Eliseo Guallar (1,2,3)

(1) Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, (2) Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, (3) Johns Hopkins Center for Excellence in Environmental Public Health Tracking, Johns Hopkins University Bloomberg School of Public Health, (4) Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, (5) Department of Medicine, Johns Hopkins School of Medicine, and (6) Department of Health Policy and Management, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA

Address correspondence to A. Navas Acien, Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, 615 N. Wolfe St., Office W7033B, Baltimore, MD 21205-2223 USA. Telephone: (410) 502-4267. Fax: (410) 955-0476. E-mail: anavas@jhsph.edu

This work was supported by National Institute of Environmental Health Sciences grant 1R01 ES012673-01. A.N.-A., R.A.S., T.A.B., and E.G. were supported by the Johns Hopkins Center of Excellence in Environmental Public Health Tracking (Centers for Disease Control and Prevention grant U50CCU322417).

The authors declare they have no competing financial interests.
Table 1. In vitro studies of arsenic exposure and
glucose metabolism outcomes.

Source Type of cell/tissue Compound

Signal transduction and gene expression

Macfarlane et al. 1997 Pancreatic [beta]-cells Arsenite
Macfarlane et al. 1999 Pancreatic [beta]-cells Arsenite
Elrick and Docherty 2001 Pancreatic [beta]-cells Arsenite
Wauson et al. 2002 C3H 10T1/2 Arsenite
 preadipocytes
Salazard et al. 2004 3T3-F442A Arsenite
 preadipocytes

Glucose uptake in cultured cells

Warren et al. 1986 BHK-21 cells Arsenite
Widnell et al. 1990 BHK-21 cells Arsenite
Pasternak et al. 1991 BHK-21 cells Arsenite
Liebl et al. 1992 MDCK dog cells Arsenite
Sviderskaya et al. 1996 BHK cells Arsenite
 3T3-L1 adipocytes
McDowell et al. 1997 L6 rat muscle cells Arsenite
Fladeby and Serck- Bovine adrenal cells Arsenite
 Hanssen 1999
Bazuine et al. 2003 3T3-L1 adipocytes Arsenite
Bazuine et al. 2004 3T3-L1 adipocytes Arsenite
Walton et al. 2004 3T3-L1 adipocytes Arsenite
 [MAs.sup.III]O
 [DMAs.sup.III]I
 Arsenate
 [MAs.sup.V]
 [DMAs.sup.V]

 Arsenite
 [MAs.sup.III]O
 [DMAs.sup.III]I

Miscellaneous experiments

Short et al. 1965 Rat hemidiaphragms Arsenite
 Epidydimal fat pads Arsenate
Dixit and Lazarow 1967 Epidydimal fat pads Arsenite
Brazy et al. 1980 Rabbit kidney tubules Arsenate
Hunder et al. 1993 Rat jejunal segments Arsenite
 Arsenate

Source Dose (ppm) Incubation

Signal transduction and gene expression

Macfarlane et al. 1997 37.5 0.33 hr
Macfarlane et al. 1999 75 0.5 hr
Elrick and Docherty 2001 75 0.5 hr
Wauson et al. 2002 0.45 2 months
Salazard et al. 2004 0.0017, 3 days
 0.003

Glucose uptake in cultured cells

Warren et al. 1986 3.75 2 hr
Widnell et al. 1990 15 2 hr
Pasternak et al. 1991 4.5-7.5 2 hr
Liebl et al. 1992 37.5-75 1 hr
Sviderskaya et al. 1996 7.5-22.5 2 hr
McDowell et al. 1997 7.5-112.5 0.5 hr
Fladeby and Serck- 1.88-18.8 1 hr
 Hanssen 1999
Bazuine et al. 2003 0.75-75 0.5 hr
Bazuine et al. 2004 3.75-750 0.5 hr
Walton et al. 2004 1.57, 7.5 4 hr
 0.08, 0.4
 0.15, 0.75
 7.5, 75
 7.5, 75
 7.5, 75
 0.4, 0.8, 1.5 24 hr
 0.02, 0.04, 0.08
 0.04, 0.08, 0.15

Miscellaneous experiments

Short et al. 1965 75 1-3 hr
 75
Dixit and Lazarow 1967 0.75-7,500 3 hr
Brazy et al. 1980 0.75-375 0.5 hr
Hunder et al. 1993 0.19-18.9 2 hr
 0.19-187.5

 Outcomes and results
Source (compared with controls)

Signal transduction and gene expression

Macfarlane et al. 1997 [up arrow] IUF-1 dependent gene
 expression PI-3 kinase
 independent, SAPK2/p38
 involved

Macfarlane et al. 1999 [up arrow] IUF-1 translocation from
 cytoplasm to nucleus PI-3
 kinase independent; SAPK2/p38
 involved

Elrick and Docherty 2001 [up arrow] IUF-1 translocation from
 cytoplasm to nucleus PI-3
 kinase independent, SAPK2/p38
 involved

Wauson et al. 2002 [down arrow] PPAR[gamma] mRNA
 [down arrow] Pioglitazone-stimulated
 adipocyte differentiation

Salazard et al. 2004 [up arrow] Expression of PPAR[gamma] and
 C/EBP[alpha] (genes with
 important roles in adipose
 determination)

Glucose uptake in cultured cells

Warren et al. 1986 [up arrow] Basal glucose uptake; =
 insulin-stimulated glucose
 uptake = amino acid uptake

Widnell et al. 1990 [up arrow] Basal glucose uptake;
 [up arrow] glucose transporter
 translocation (reversible)

Pasternak et al. 1991 [up arrow] Basal glucose uptake
 (reversible when arsenite
 removed) Fast and reversible
 translocation of glucose
 receptor

Liebl et al. 1992 [down arrow] Basal glucose uptake, dose
 dependent

Sviderskaya et al. 1996 [up arrow] Basal glucose uptake, dose
 dependent
 [up arrow] Glucose transporter
 translocation in both types
 of cells

McDowell et al. 1997 [up arrow] Basal glucose uptake, dose
 dependent but maximal with
 37.5 ppm
 [up arrow] GLUT1 and GLUT4 in cell
 membrane, PI-3 kinase
 independent
 [up arrow] Insulin-stimulated glucose
 uptake

Fladeby and Serck- [up arrow] Basal glucose uptake up to
 Hanssen 1999 7.5 ppm, then plateau PI-3
 kinase independent, SAPK2/p38
 partly involved

Bazuine et al. 2003 [up arrow] Basal glucose uptake up to
 37.5 ppm, then [down arrow]
 [down arrow] Insulin-stimulated glucose
 uptake
 [up arrow] GLUT4 and GLUT1 translocation
 (but less than insulin) PI-3
 kinase independent; no
 changes in IR[beta], IRS-1,
 IRS-2 No phosphorylation of
 PKB; PKC-[lambda]/[zeta] and
 SAPK2/p38 involved

Bazuine et al. 2004 [up arrow] Basal glucose uptake up to
 37.5 ppm Dexamethasone
 [down arrow] arsenite glucose
 uptake SAPK2/p38 involved
Walton et al. 2004 = basal glucose uptake at 1.50 ppm,
 [down arrow] at 7.5 ppm, [down arrow]
 insulin-stimulated
 = basal glucose uptake at 0.08 ppm,
 [down arrow] at 0.4 ppm, [down arrow]
 insulin-stimulated
 = basal glucose uptake all doses,
 [down arrow] insulin-stimulated
 [up arrow] basal glucose uptake at
 7.5 ppm, [down arrow] at
 75 ppm, = insulin-stimulated
 = basal glucose uptake all doses,
 [down arrow] insulin-stimulated
 = basal and insulin-stimulated glucose
 uptake all doses,
 PI-3 kinase independent. No changes in
 IR[beta] and IRS-2
 [MAs.sup.III]O and [DAs.sup.III]I,
 but not arsenite IRS-1, [up arrow]
 phosphorylation of IRS-1
 Arsenite, [MAs.sup.III]O and
 [DAs.sup.III]I [down arrow]
 phosphorylation of PKB/Akt
 Arsenite, [MAs.sup.III]O and
 [DAs.sup.III]I [down arrow] GLUT4
 translocation in insulin-treated cells
 Dose-dependent [down arrow]
 insulin-stimulated glucose uptake
 = insulin-stimulated glucose uptake at
 0.02 ppm, [down arrow] at 0.04 and 0.08
 = insulin-stimulated glucose uptake all
 doses

Miscellaneous experiments

Short et al. 1965 [up arrow] Basal glucose uptake in
 hemidiaphragms; [up arrow]
 uptake with arsenate in
 fat pads = insulin stimulated
 glucose uptake in
 hemidiaphragm; [down arrow]
 uptake with arsenite in fat
 pad

Dixit and Lazarow 1967 [up arrow] Basal glucose oxidation up
 to 7.5 ppm

Brazy et al. 1980 [down arrow] Fluid, phosphate, and glucose
 absorption (lumen to bath)

Hunder et al. 1993 [down arrow] Intestinal glucose transfer
 dose dependent (= arsenate
 < 7.5 ppm)

Abbreviations: [up arrow], increase; [down arrow], decrease; = similar
levels; BHK-21 cells, baby hamster kidney cells (contain predominantly
GLUT1); C/EBP[alpha], CCAAT/enhancer binding protein; [DAs.sup.III]I,
iodo-dimethylarsine; [DMAs.sup.V], dimethylarsinic acid; GLUT, glucose
transporter; IR[beta]: insulin receptor [beta]; IRS, insulin receptor
substrate; IUF-1, insulin upstream factor-1 (also called homeodomain
transcription factor PDX1); [MAs.sup.III]O, methylarsine oxide;
[MAs.sup.V], monosodium methyl arsenate; MDCK dog cells, Madin-Darby
canine kidney cells; PI-3 kinase, phosphatydilinositol-3 kinase;
PKB, protein kinase B; PKC, protein kinase C; PPAR[gamma], peroxisome
proliferative-activated receptor [gamma], SAPK2, stress activator
protein kinase 2 (also called p38 mitogen-activated protein kinase).
1 ppm = 13.35 [micro]M. Basal glucose uptake, glucose uptake in the
absence of insulin.

Table 2. Experimental characteristics and ratio of glucose uptake in
peripheral cell lines exposed to arsenite and insulin compared with
insulin and arsenite alone.

 Experiment characteristics

 Incubation Arsenite Insulin
Source Type of cell (hr) (ppm) (nM)

Warren et al. 1986 BHK-21 cells 2 3.75 100
McDowell et al. 1997 L6 rat muscle 0.5 37.5 100
 cells
Bazuine et al. 2003 3T3-L1 adipocytes 0.5 37.5 100
Walton et al. 2004 3T3-L1 adipocytes 4 1.50 1,000
Walton et al. 2004 3T3-L1 adipocytes 4 7.49 1,000

 Ratio of glucose
 uptake vs.

Source Insulin Arsenite

Warren et al. 1986 0.94 0.91
McDowell et al. 1997 1.42 1.21
Bazuine et al. 2003 0.57 1.33
Walton et al. 2004 0.60 0.55
Walton et al. 2004 0.20 0.33

BHK-21 cells, baby hamster kidney cells. For arsenite,
1 ppm = 13.35 [micro]M.

Table 3. In vivo studies of arsenic exposure and glucose metabolism.

 Experimental
Source animal n

Judd 1979 Field mice 19
Ghafghazi et al. 1980 Rats 12
Hughes and Thompson 1996 B6C3[F.sub.1] mice 72
Aguilar et al. 1997 Wistar rats 20
Cobo and Castineira 1997 Wistar rats 21
Biswas et al. 2000 Bengal goats 12
Arnold et al. 2003 Fischer rats 480
Pal and Chatterjee 2004a Wistar rats 18
Pal and Chatterjee 2004b Wistar rats 18
Pal and Chatterjee 2005 Wistar rats 18

Source Compound (route)

Judd 1979 Methanearsonate (po in water)
Ghafghazi et al. 1980 Arsenite (ip)
Hughes and Thompson 1996 Arsenate (po in water)
Aguilar et al. 1997 Arsenate (po in food)
Cobo and Castineira 1997 Arsenite (po in water)
Biswas et al. 2000 Arsenite (po in capsule)
Arnold et al. 2003 Monomethylarsenic (po in food)
Pal and Chatterjee 2004a Arsenite (ip)
Pal and Chatterjee 2004b Arsenite (ip)
Pal and Chatterjee 2005 Arsenite (ip)

 Daily dose
Source (ppm) Duration

Judd 1979 1,000 30 days
Ghafghazi et al. 1980 5-10 7 days
Hughes and Thompson 1996 0.025-2.5 28 days
Aguilar et al. 1997 5 10 weeks
Cobo and Castineira 1997 17.75 1st week
 up to 100 8th week
Biswas et al. 2000 25 12 weeks
Arnold et al. 2003 50-1,300 2 years
Pal and Chatterjee 2004a 5.55 21 days
Pal and Chatterjee 2004b 5.55 30 days
Pal and Chatterjee 2005 5.55 30 days

 Outcomes and results
Source (compared with controls)

Judd 1979 [down arrow] Blood glucose, = fluid and
 food consumption
Ghafghazi et al. 1980 [up arrow] Glucose levels after glucose
 tolerance test, dose
 dependent
Hughes and Thompson 1996 [down arrow] Plasma glucose, = fluid and
 food consumption
Aguilar et al. 1997 = Plasma glucose levels
Cobo and Castineira 1997 Delayed glucose clearance
 after glucose tolerance test
 = Basal insulin levels in vivo
Biswas et al. 2000 [up arrow] Blood glucose at week 6 and
 [up arrow][up arrow] at
 week 12
Arnold et al. 2003 = Blood glucose levels up to
 400 ppm, [down arrow] with
 1,300 ppm
Pal and Chatterjee 2004a [down arrow] Blood glucose (reversed with
 methionine)
 = Body, liver, kidney weight
Pal and Chatterjee 2004b [down arrow] Blood glucose (reversed with
 N-acetylcysteine)
Pal and Chatterjee 2005 [down arrow] Blood glucose (reversed with
 methionine)

Abbreviations: ip, intraperitonea1; po, per oral; [up arrow], increase;
[down arrow], decrease.

Table 4. Epidemiolopic studies of arsenic exposure and diabetes.

Source Design Country Population

General populations, high arsenic exposure

Lai et al. 1994 CS Taiwan Survey of participants
 in high-arsenic area
Tsai et al. 1999 RCO Taiwan Deaths in 1971-1994
Tseng et al. CO Taiwan Survey of participants
 2000 in high-arsenic area
Wang et al. CS Taiwan National Health
 2003 Insurance Database
Rahman et al. CS Bangla- Survey participants
 1998 desh in high- and
 low-arsenic areas
Rahman et al. CS Bangla- Survey participants
 1999 desh in high-arsenic area

Occupational populations, high arsenic exposure

Mabuchi et al. RCO U.S. Pesticide workers,
 1980 Baltimore, MD
Enterline and RCO U.S. Copper smelter
 Marsh 1982 workers, Washington
 State
Lagerkvist and CS Sweden Copper smelter
 Zetterlund 1994 workers, other jobs
Rahman and CC Sweden Copper smelter
 Axelson 1995 workers
Rahman et al. CC Sweden Deaths in glass
 1996 industry area
Jensen and CS Denmark Taxidermists, wood
 Hansen 1998 workers, other jobs
Bartoli et al. RCO Italy Glass industry
 1998 workers
Lubin et al. 2000 RCO U.S. Copper smelter
 workers, Montana
Tollestrup et al. RCO U.S. Children < 4 km of
 2003 Copper smelter

General populations, low to moderate arsenic exposure

Ward and Pim CC UK Hospital based
 1984
Ruiz-Navarro CC Spain Hospital based
 et al. 1998
Lewis et al. CO U.S. Mormons
 1999
Zierold et al. CC U.S. Survey participants
 2004 with private wells

 Diabetes Cases/
Source diagnosis noncases

General populations, high arsenic exposure

Lai et al. 1994 OGTT or 86/805
 self-reported

Tsai et al. 1999 Death certificate 531 deaths
Tseng et al. OGTT 41/405
 2000
Wang et al. ICD-9 250 27,543/
 2003 ICD-9 A181 678,791
Rahman et al. Self-reported 46/971
 1998 symptoms +
 glucosuria +
 OGTT
Rahman et al. Glucosuria 263/1,332
 1999

Occupational populations, high arsenic exposure

Mabuchi et al. Death certificate 2 deaths
 1980
Enterline and Death certificate 12 deaths
 Marsh 1982
Lagerkvist and Self-reported 4/85
 Zetterlund 1994 type 2 diabetes
Rahman and Death certificate, 12/31
 Axelson 1995 medical record
Rahman et al. Death certificate 240/2,216
 1996
Jensen and HbA1c 5/59
 Hansen 1998
Bartoli et al. Death certificate 3 deaths
 1998
Lubin et al. 2000 Death certificate 54 deaths
Tollestrup et al. Death certificate 16/3,116
 2003

General populations, low to moderate arsenic exposure

Ward and Pim NR 87/30
 1984
Ruiz-Navarro NR 38/49
 et al. 1998
Lewis et al. Death certificate 55/4,003
 1999
Zierold et al. Self-reported 67/1118
 2004

 Men Age range
Source (%) (year)

General populations, high arsenic exposure

Lai et al. 1994 43 30-69
Tsai et al. 1999 35 All ages
Tseng et al. 50 Mean 47
 2000
Wang et al. 43 25-65+
 2003
Rahman et al. 59 30-60+
 1998
Rahman et al. 61 30-60+
 1999

Occupational populations, high arsenic exposure

Mabuchi et al. 75 < 20-40+
 1980 at hire
Enterline and 100 < 20-69
 Marsh 1982 at hire
Lagerkvist and 100 Mean 57
 Zetterlund 1994
Rahman and 100 30-74 at
 Axelson 1995 death
Rahman et al. 100 45-75+
 1996
Jensen and 87 Mean 37
 Hansen 1998
Bartoli et al. 100 < 40-65+
 1998
Lubin et al. 2000 100 < 20-30+
 at hire
Tollestrup et al. 58 < 14
 2003

General populations, low to moderate arsenic exposure

Ward and Pim 65 18-78
 1984
Ruiz-Navarro 39 NR
 et al. 1998
Lewis et al. 52 < 50-80+
 1999
Zierold et al. NR Mean 62
 2004

 Arsenic Levels, exposed
Source assessment vs. reference

General populations, high arsenic exposure

Lai et al. 1994 CEI village > 15 vs. 0 ppm-year
 drinking water

Tsai et al. 1999 Living in HAA HAA vs. no HAA
Tseng et al. CEI village > 17 vs. < 17
 2000 drinking water ppm-year
Wang et al. Living in HAA HAA vs. no HAA
 2003
Rahman et al. Living in HAA Keratosis vs.
 1998 and keratosis no keratosis
Rahman et al. CEI village > 10 vs. 0 ppm-year
 1999 drinking water

Occupational populations, high arsenic exposure

Mabuchi et al. Job title Workers vs. general
 1980 population
Enterline and Job title Workers vs. general
 Marsh 1982 population
Lagerkvist and Job title Workers vs. other
 Zetterlund 1994 workers
Rahman and Air levels ~ 5 vs. 0 mg/[m.sup.3]
 Axelson 1995
Rahman et al. Job title Workers vs. other
 1996 workers
Jensen and Job title Workers vs. general
 Hansen 1998 population
Bartoli et al. Job title Workers vs. general
 1998 population
Lubin et al. 2000 Job title Workers vs. general
 population
Tollestrup et al. Years of [greater than or
 2003 residency equal to] l0 vs. < 1 year

General populations, low to moderate arsenic exposure

Ward and Pim Plasma levels 75th vs. 25th
 1984 (NAA) percentile
Ruiz-Navarro Urinary levels 75th vs. 25th
 et al. 1998 (AAS) percentile
Lewis et al. CEI community > 4 vs. < 1
 1999 drinking water ppm-year
Zierold et al. Subject > 10 vs. < 2 ppb
 2004 drinking water

 RR of diabetes
Source (95% CI) Adjusted for

General populations, high arsenic exposure

Lai et al. 1994 10.1 (1.30-77.9) Age, sex, BMI,
 physical
 activity
Tsai et al. 1999 1.46 (1.28-1.67) Age, sex
Tseng et al. 2.10 (1.10-4.20) Age, sex, BMI
 2000
Wang et al. 2.69 (2.65-2.73) Age, sex
 2003
Rahman et al. 5.90 (2.90-11.6) Age, sex, BMI
 1998
Rahman et al. 2.10 (1.10-4.20) Age, sex
 1999

Occupational populations, high arsenic exposure

Mabuchi et al. 0.47 (0.12-1.88) Age, sex, period
 1980
Enterline and 0.85 (0.48-1.49) Age
 Marsh 1982
Lagerkvist and 9.61 (0.53-173) Crude
 Zetterlund 1994
Rahman and 3.30 (0.50-30.0) Age
 Axelson 1995
Rahman et al. 1.40 (0.90-2.10) Age
 1996
Jensen and 4.43 (0.47-42.0) Age
 Hansen 1998
Bartoli et al. 0.34 (0.09-0.88) Age
 1998
Lubin et al. 2000 0.83 (0.63-1.08) Age
Tollestrup et al. 1.60 (0.36-1.16) Crude
 2003

General populations, low to moderate arsenic exposure

Ward and Pim 1.09 (0.79-1.49) Crude
 1984
Ruiz-Navarro 0.87 (0.50-1.53) Crude
 et al. 1998
Lewis et al. 0.65 (0.34-1.24) Age, sex
 1999
Zierold et al. 1.02 (0.49-2.15) Age, sex, BMI,
 2004 smoking

Abbreviations: AAS, atomic absorption spectrometry; BMI, body mass
index; CC, case-control; CEI, cumulative exposure index: [SIGMA]
arsenic levels in drinking water; x time of exposure; (i indicates
specific village); CO, cohort; CS, cross-sectional; HAA, high-arsenic
area; HbA1c, hemoglobin A1c; ICD-9, International Classification of
Diseases, Ninth revision; NAA, neutron activation analysis; NR, not
reported; OGTT, oral glucose tolerance test, criteria for a positive
test based on the WHO criteria; RCO, retrospective cohort; RR, relative
risk.

Table 5. Criteria for evaluating the design and data analysis of
epidemiologic studies on arsenic and diabetes. (a)

 Taiwan and Bangladesh

 Tsai Tseng
 Lai et al. et al. et al.
 1994 1999 2000

All studies (n = 19)

 Diabetes diagnosis based on Y N Y
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the N N N
 individual level
 Exposure assessed using a N N N
 biomarker of exposure
 Control for established Y N Y
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases Y -- --
 at least 70% (b)
 Noncases would have been cases N -- --
 if they had developed
 diabetes
 Data collected in a similar Y -- --
 manner for all participants
 Cases interviewed within N -- --
 6 months of diagnosis
 Interviewer blinded with Y -- --
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all Y -- --
 participants were
 interviewed was the same (c)
 Same exclusion criteria Y -- --
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was -- N Y
 independent of exposure
 Intensity of search of disease -- N Y
 independent of exposure
 status

 Taiwan and Bangladesh

 Wang Rahman Rahman
 et al. et al. et al.
 2003 1998 1999

All studies (n = 19)

 Diabetes diagnosis based on N N N
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the N N N
 individual level
 Exposure assessed using a N N N
 biomarker of exposure
 Control for established N N N
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases Y N Y
 at least 70% (b)
 Noncases would have been cases N N N
 if they had developed
 diabetes
 Data collected in a similar Y N N
 manner for all participants
 Cases interviewed within N N N
 6 months of diagnosis
 Interviewer blinded with -- N N
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all -- N N
 participants were
 interviewed was the same (c)
 Same exclusion criteria Y N N
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was -- -- --
 independent of exposure
 Intensity of search of disease -- -- --
 independent of exposure
 status

 Occupational populations

 Lagerkvist
 Mabuchi Enferline and
 et al. and Marsh Zetterlund
 1980 1982 1994

All studies (n = 19)

 Diabetes diagnosis based on N N N
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the N N N
 individual level
 Exposure assessed using a N N N
 biomarker of exposure
 Control for established Y N N
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases -- -- N
 at least 70% (b)
 Noncases would have been cases -- -- N
 if they had developed
 diabetes
 Data collected in a similar -- -- N
 manner for all participants
 Cases interviewed within -- -- N
 6 months of diagnosis
 Interviewer blinded with -- -- N
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all -- -- N
 participants were
 interviewed was the same (c)
 Same exclusion criteria -- -- N
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was N N --
 independent of exposure
 Intensity of search of disease N N --
 independent of exposure
 status

 Occupational populations

 Rahman and Rahman Jensen
 Axelson et al. and Hansen
 1995 1996 1998

All studies (n = 19)

 Diabetes diagnosis based on N N N
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the Y N N
 individual level
 Exposure assessed using a N N N
 biomarker of exposure
 Control for established N N N
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases -- -- N
 at least 70% (b)
 Noncases would have been cases N N Y
 if they had developed
 diabetes
 Data collected in a similar Y Y Y
 manner for all participants
 Cases interviewed within N N N
 6 months of diagnosis
 Interviewer blinded with N N Y
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all Y Y N
 participants were
 interviewed was the same (c)
 Same exclusion criteria Y N N
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was -- -- --
 independent of exposure
 Intensity of search of disease -- -- --
 independent of exposure
 status

 Occupational populations

 Bartoli Lubin Tollestrup
 et al. et al. et al.
 1998 2000 2003

All studies (n = 19)

 Diabetes diagnosis based on N N N
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the N N Y
 individual level
 Exposure assessed using a N N N
 biomarker of exposure
 Control for established N N N
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases -- -- --
 at least 70% (b)
 Noncases would have been cases -- -- --
 if they had developed
 diabetes
 Data collected in a similar -- -- --
 manner for all participants
 Cases interviewed within -- -- --
 6 months of diagnosis
 Interviewer blinded with -- -- --
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all -- -- --
 participants were
 interviewed was the same (c)
 Same exclusion criteria -- -- --
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was N N N
 independent of exposure
 Intensity of search of disease N N N
 independent of exposure
 status

 Other populations

 Ruiz-
 Ward Navarro
 and Pim et al.
 1984 1998

All studies (n = 19)

 Diabetes diagnosis based on N N
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the Y Y
 individual level
 Exposure assessed using a Y Y
 biomarker of exposure
 Control for established N N
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases N N
 at least 70% (b)
 Noncases would have been cases N N
 if they had developed
 diabetes
 Data collected in a similar N N
 manner for all participants
 Cases interviewed within N N
 6 months of diagnosis
 Interviewer blinded with N N
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all N N
 participants were
 interviewed was the same (c)
 Same exclusion criteria N N
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was -- --
 independent of exposure
 Intensity of search of disease -- --
 independent of exposure
 status

 Other populations

 Lewis Zierold
 et al. et al.
 1999 2004

All studies (n = 19)

 Diabetes diagnosis based on N N
 fasting glucose levels or
 oral glucose tolerance tests
 Exposure assessed at the N Y
 individual level
 Exposure assessed using a N N
 biomarker of exposure
 Control for established N Y
 diabetes risk factors in
 addition to age

Case-control and cross-sectional studies (n = 11)

 Response rate among noncases -- N
 at least 70% (b)
 Noncases would have been cases -- N
 if they had developed
 diabetes
 Data collected in a similar -- Y
 manner for all participants
 Cases interviewed within -- N
 6 months of diagnosis
 Interviewer blinded with -- Y
 respect to the case status
 of the person
 interviewed (c)
 Time period during which all -- Y
 participants were
 interviewed was the same (c)
 Same exclusion criteria -- Y
 applied to all participants

Cohort studies (n = 8)

 Loss to follow-up was Y --
 independent of exposure
 Intensity of search of disease Y --
 independent of exposure
 status

Abbreviations: --, not applicable; N, no; Y, yes.

(a) Criteria modified from Longnecker et al. (1988). (b) Not applicable
to two case-control studies based only on deaths (Rahman and Axelson
1995; Rahman et al. (1996). (c) Not applicable to the study using the
National Health Insurance Database from Taiwan (Wang et al. 2003).
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Author:Guallar, Eliseo
Publication:Environmental Health Perspectives
Date:May 1, 2006
Words:10784
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