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Bone mineral density and vitamin D level compared to lifestyle in resident physicians.

Introduction

Resident training comes with a demanding lifestyle that leaves little time for the physical activity and adequate sunlight exposure that are key elements in maintaining overall bone health. There are few studies in the literature that have looked at residency training and its effects on bone mineral density in a relatively young and healthy patient population. One such study from India did attempt to investigate this problem; they measured bone mineral density (BMD) in 214 resident physicians and found a lower BMD in this population with contributing factors being lower body mass index (BMI) and a lower amount of physical activity. (1) Data have shown that the United States overall has a moderate rate of fracture compared to other countries; however, Caucasian Americans specifically have the highest risk of fracture. (2) There have been no studies to our knowledge looking at BMD in resident physicians at a North American institution with a largely Caucasian demographic.

Fracture risk is determined by both bone structure and bone mineral mass. Of course bone structure is non-modifiable, but bone mineral mass can be affected by lifestyle choices. Peak bone mass (PBM) is the amount of bone present at the end of skeletal maturation, sixty percent of which is genetically determined and forty percent of which is modifiable. (3) Positive interventions such as a diet high in calcium, protein, and vitamin D as well as regular weight-bearing physical activity play a role. It has been shown that if areal bone mineral density (aBMD), or mass per unit of area, in a young adult is 10% greater than the mean, then the onset of osteoporosis is expected to be delayed by 13 years. (3) This prediction highlights the importance of bone quality and bone health, not just in the elderly, but in young and seemingly healthy individuals.

Physical activity has been shown to contribute significantly to bone mineral density in the young adult population. A study of 80 young Caucasian women followed for a period of ten years (ages 12-22) showed that load-bearing exercise such as walking, running, or aerobics was the predominant modifiable factor in determining BMD in that population. (4) Studies looking specifically at resident physicians and their amount of physical activity have shown a deficiency in that area as well. (5, 6, 7)

Our hypothesis was that resident physicians have lower vitamin D levels and lower BMD because of demands in the workplace that involve large amounts of time indoors during peak daylight hours and little time for physical activity.

We sought to investigate this assertion by assessing vitamin D level through a routine blood test and BMD through a dual-energy X-ray absorptiometry (DEXA) scan. We correlated these values with a survey about hours worked, physical activity, and sun exposure.

Methods

Approval for this study was granted by the West Virginia University Institutional Review Board and all subjects gave voluntary informed consent. Participants in this study included resident physicians from our facility in all specialties and in all post graduate year (PGY) positions. Exclusion criteria included the following: pregnant and lactating women; those who had received steroids, anti-tuberculosis, or antiepileptic medications within the past two years; those who had fractures within the past two years; those who were on calcium and vitamin D supplements within the previous three months; and those with any other medical disorder affecting BMD. Participants were paid ten dollars in exchange for participation in this study.

There were three sections of the study. Subjects were asked to complete an online survey, have blood drawn to check vitamin D levels, and undergo a DEXA scan. In addition to demographic data such as age, weight, height, and residency program, the online survey asked questions related to sun exposure and physical activity. Physical activity was assessed in a manner similar to the Global Physical Activity Questionnaire (GPAQ) developed by the World Health Organization (WHO) and was reported as minutes/week of moderate to vigorous physical activity. (8) Sun exposure was assessed using a sun exposure score developed by Hanwell et al. which assessed minutes per week outdoors with varying levels of skin exposure. A maximum score of 56 would indicate spending greater than 30 minutes outside in the sun wearing a bathing suit every day of the week. (9) Specific clothing worn and sunscreen use were not included in the Hanwell assessment tool for ease of use and more accurate participant recall, and thus were not included in this study for similar reasons.

Following completion of the survey, BMD at the lumbar spine and proximal femur was assessed using DEXA (Discovery Model SL, Hologic, Inc., Bedford, MA) which was operated by a trained technician. A T-score (based on normative Caucasian data) for each participant was then calculated and recorded. Participants were also asked to provide a blood sample to determine a 25-(OH) vitamin D3 level. The 25-(OH) vitamin D3 measurements obtained were based on normal reference ranges from our laboratory and graded as normal (>30ng/ml), insufficient (20-29ng/ml), or deficient (<20ng/ml).

Statistical analysis was performed to determine a correlation between BMD and vitamin D level compared to data collected from the survey.

A Pearson correlation coefficient was used to calculate either a positive or negative correlation. A p value < 0.05 was determined to be statistically significant.

Results

Forty-four (20 males and 24 females) resident and fellowship physicians were enrolled in the study. Forty-one subjects completed the online survey and 38 provided 25-hydroxy vitamin D serum levels. Forty subjects underwent DEXA scan measurements of the lumbar spine and hip. Forty-three of the participants reported post graduate year (PGY) year of training at the time of the study. The most represented group was PGY-2 with 11 (27%) subjects participating. Orthopaedic surgery was the most represented program with nine participants (22%). Caucasian was the most represented race at 32 participants (78%) followed by Asian with eight participants (20%), and one African American (2.4%) (Table 1).

The averages of certain characteristics of the participants are summarized in Table 2. Of note, the average age of all subjects was 29.61 [+ or -] 2.25 years (30.00 [+ or -] 1.97 years for males and 29.33 [+ or -] 2.43 years for females) and the average total work hours for all subjects was 59.63 [+ or -] 11.93 hours (60.69 [+ or -] 10.93 hours for males and 58.92 [+ or -] 12.74 hours for females), which was well below 80 hours per week. Of the thirty-eight (16 males and 22 females) subjects for whom a serum vitamin D level was measured, the average was 29.08 ng/ml [+ or -] 13.77ng/ ml for all subjects and 25.35 [+ or -] 8.57 ng/mL for all males which both fell into the insufficient range. Females averaged 31.79 [+ or -] 16.23 ng/mL which is at the lower limit of normal. Sixty-one percent of all participants had serum vitamin D levels that were below 30ng/ml and 31.5% were less than 20ng/mL which is in the deficient range (Table 2).

Out of the 40 subjects who completed a DEXA scan, 17 (42.5%) were osteopenic (>-2.5 T-score < -1.0) and three (7.5%) were osteoporotic (T score <= -2.5) (Table 3). There was a significant positive correlation in bone mineral density at L1 compared to work hours in males (p=0.0446) and a significant positive correlation in bone mineral density at the greater trochanter compared to BMI in females (p = 0.0136) (Table 4).

Vitamin D levels were also compared to various factors using Pearson's correlation coefficient for both males and females. There were significant positive correlations between age and vitamin D level (p = 0.0073) and PGY and vitamin D level (p = 0.0115) in males. There were no significant correlations between vitamin D level and the various characteristics in females (Table 4). Blood samples were taken from participants between the timeframe of June through March and showed a decrease in vitamin D level in both males and females from the summer months to the winter months (Figure 1). The decrease was most notable among males, although the correlation was not significant in either group.

Discussion

The average vitamin D for all subjects in this study was 29.08ng/ mL with 31.5% falling into the deficient range (< 20 ng/mL) (Table 2). This finding is in accordance with a study from Boston on vitamin D levels in pediatric residents, which found an average of 26.8 ng/mL with 25% falling into the deficient range. (10) Looking at correlations between vitamin D level and various factors in the subjects, we found significant positive correlations in vitamin D level compared to age and PGY in the male subjects (Table 4). This finding could suggest that, as one progresses through their training program, there is more time to devote to outdoor recreational activities, as day-to-day responsibilities could be delegated to lower level residents. We did not see a significant correlation between vitamin D level and sun exposure score in either males or females as would be expected.

As sun exposure does play a role in vitamin D metabolism, we opted to look at the trend in vitamin D level for males and females during the nine month period which began during the summer months and ended after the winter months (June-March). (11) As expected, we did see a downward trend as summer progressed to winter where there is predictably less time for optimum sun exposure (Figure 1).

A T-score is based on the bone mineral density of a young adult Caucasian female. The World Health Organization (WHO) defines osteopenia as a T-score < -1.0 and osteoporosis as a T score <= -2.5, which is the criteria used in this study. The WHO reports osteopenia and osteoporosis rates in this demographic as 14% and 0.6%, respectively. (12) In this study, the percentages of osteopenia and osteoporosis are much higher (42.5% and 7.5%, respectively) than would be expected for this cohort based on the WHO figures (Table 3). It should be noted, however, that a diagnosis of osteoporosis in this age group should not be based on T-score alone. (13)

We also looked at the BMD values obtained from the DEXA scan at the lumbar spine and the greater trochanter and compared them to various factors in the male and female subjects. Our DEXA software reported BMD values for the greater trochanter only but included the femoral neck and Ward's triangle for T-score calculations.

In the males in our study, there was a significant positive correlation in work hours and BMD at L1 (p =0.0045) (Table 4) which could be due to physical activity gained while walking throughout the hospital, climbing stairs, etc. and could be an avenue for further investigation.

In females, we found a significant correlation between BMI and BMD at the greater trochanter (p = 0.0136) (Table 4). This finding is in accordance with basic bone physiology in which bones remodel and become stronger in response to increases in compressive forces. (14)

There were some limitations to this study. The major overall limitation was the number of subjects enrolled. Recruiting resident physicians for participation proved difficult. The serum samples for vitamin D could only be collected during certain hours and the DEXA scanner was even more constrained in terms of available hours. Values for BMI were based on self-reported height and weight during the survey and were not direct measurements taken by a research assistant. This limitation could represent bias of the subjects in terms of their perceived height and weight. Another limitation was that the survey data did not include information on dietary intake, which would provide valuable information that could potentially explain changes in bone mineral density and vitamin D levels in this cohort.

Conclusion

Current US Preventive Task Force recommendations are against routine bone density screening in this age group and indicate there is insufficient evidence for supplementation beyond the recommended dietary allowance of 600 international units of vitamin D and 1000 mg of calcium daily, in asymptomatic males and females under age 65. (15, 16) However, the results of this study point out potential long-term consequences.

In a young, presumably healthy population, we found an average vitamin D level in the insufficient range (29.08 ng/mL) and higher percentages of osteopenia and osteoporosis (42.5% and 7.5%, respectively) than would be expected for this age group based on World Health Organization data. Although there were no significant correlations in lower bone mineral density and lower vitamin D level compared to factors such as increasing work hours, less frequent physical activity, and reduced sun exposure, further study is indicated to determine what lifestyle factors unique to this population have an effect on the increased prevalence of osteopenia and osteoporosis and lower vitamin D levels that were found in this study. Further study may provide insight as to what these findings in younger aged physicians mean for their future bone health, and whether vitamin D or calcium supplementation may be warranted in this population. More data may also indicate whether more frequent monitoring of bone mineral density may be appropriate for those with reduced sun exposure and infrequent physical activity, and what effect this monitoring could have on improving bone health in the physician population.

[FIGURE 1 OMITTED]

References

(1.) Multani SK, Sarathi V, Shivane V, Bandgar TR, Menon PS, Shah NS. Study of bone mineral density in resident doctors working at a teaching hospital. J Postgrad Med. 2010;56(2):65-70.

(2.) Kanis JA, Oden A, McCloskey EV, Johansson H, Wahl DA, Cooper C. "A systematic review of hip fracture incidence and probability of fracture worldwide." Osteoporos Int. (2012);23:2239-2256.

(3.) Rizzoli R, Bianchi ML, Garabedian M, McKay HA, Moreno LA. Maximizing bone mineral mass gain during growth for the prevention of fractures in the adolescents and the elderly. Bone. 2010;46(2):294-305.

(4.) Lloyd T, Petit MA, Lin H, Beck TJ. Lifestyle factors and the development of bone mass and bone strength in young women. J Pediatr. 2004;144(6):776-782.

(5.) Arora R, Lettieri C, Claybaugh JR. The effects of residency on physical fitness among military physicians. MU Med. 2004;169(7):522-525.

(6.) Olejniczak S, Glas WW. Physical Status of interns and resident physicians at Wayne County General Hospital. 1962-63. J Mich State Med Soc. 1964;63:202-204.

(7.) Suskin N, Ryan G, Fardy J, Clarke H, McKelvie R. Clinical workload decreases the level of aerobic fitness in housestaff physicians. J Cardiopulm Rehabii. 1998;18(3):216-220.

(8.) Global Physical Activity Surveillance. WHO. www.who.int/chp/steps/GPAQ/en/. Accessed 19 Apr. 2014

(9.) Hanwell H, Vieth R, Cole D, et al. Sun exposure questionnaire predicts circulating 25-hydroxyvitamin D concentrations in Caucasian hospital workers in southern Italy. J Steroid Biochem Mol Biol. 2010;121(12):334-337.

(10.) Growdon AS, Camargo Jr CA, Clark S, Hannon M, Mansback JM. Serum 25-hydroxyvitamin D levels among Boston trainee doctors in winter. Nutrients. 2012;4(3):197-207.

(11.) Deluca HF. Overview of general physiologic features and functions of vitamin D. Am J Clin Nutr. 2004;80(6 Suppl):1689S-1696S.

(12.) Diagnosis and Prevention of Osteoporosis. World Health Organ Tech Rep Ser. 2003;921:1-164

(13.) Leib ES, Lewiecki EM, Binkley N, Hamdy RC. Official Positions of the International Society for Clinical Densitometry. J Clin Densitometry. 2004;7(1):1-5.

(14.) De Laet C, Kanis JA, Oden A, et al. Body mass index as a predictor of fracture risk: a meta-analysis. Osteoporos Int. 2005;16(11):1330-1338.

(15.) "Vitamin D and calcium to prevent fractures: Preventive medication." Recommendation Summary. U.S. Preventive Services Task Force. February 2013.

(16.) "New recommended daily amounts of calcium and vitamin D." NIH Medline Plus. Winter 2011;5(4):12.

David B. McConda, MD

Department of Orthopaedics, WVU

Karim W. Boukhemis, MD

Department of Orthopaedics, WVU

Leslie J. Matthews, PharmD

School of Medicine, WVU

Colleen M. Watkins, MD

Department of Orthopaedics, WVU

Corresponding Author: David B. McConda, MD,

Dept. of Orthopaedics, WVU, PO Box 9196,

Morgantown, WV 26506-9196. Email: dmcconda@

hsc.wvu.edu.
Table 1-Demographics of participants

Post Graduate Year (PGY)    Number of
                           Participants

I                            9 (22%)
II                           11 (27%)
III                          9 (22%)
IV                           5 (12%)
V                            5 (12%)
VI                            2 (5%)

Race

Asian                        8 (20%)
African American              1 (2%)
Caucasian                    32 (78%)

Residency Program

Anesthesiology                1 (3%)
Emergency Medicine            2 (5%)
Family Medicine               3 (8%)
Internal Medicine            5 (13%)
Medicine/Pediatrics           1 (3%)
Obstetrics/Gynecology        5 (13%)
Ophthalmology                 1 (3%)
Orthopaedics                 9 (23%)
Pathology                    5 (13%)
Pediatrics                   4 (10%)
Psychiatry                    1 (3%)
Radiology                     1 (3%)
Urology                       1 (3%)

Table 2-Averages of certain characteristics and vitamin D level
among participants. (* vitamin D level is in the insufficient
range < 30 ng/mL and > 20 ng/mL)

                           Males             Females

Characteristics      Average   Std Dev   Average   Std Dev

Age                   30.00     1.97      29.33     2.43
BMI                   25.72     3.84      24.55     7.02
Hours                 60.69     10.93     58.92     12.74
Sun Exposure Score    24.71     5.91      23.00     7.00
Physical Activity    339.47    278.68    416.21    426.44
  (min/wk)
25 (OH) Vitamin      25.35 *    8.57      31.79     16.23

                          Total

Characteristics      Average   Std Dev

Age                   29.61     2.25
BMI                   25.03     5.88
Hours                 59.63     11.93
Sun Exposure Score    23.71     6.55
Physical Activity    384.39    370.27
  (min/wk)
25 (OH) Vitamin      29.08 *    13.77
  D3 (ng/mL)

Table 3. T-scores and diagnostic category

Normal                   Osteopenia            Osteoporosis

(T-score >=-1.0)   (-2.5 < T-score < -1.0)   (T-score <= -2.5)
20 (50%)                 17 (42.5%)              3 (7.5%)

Table 4-Pearson correlation coefficients (r) of vitamin D level
and bone mineral density (BMD) compared to certain characteristics
in males and females.(*p< 0.05)

                  Vitamin D Level    BMD Greater Troch

Characteristics    Male     Female    Male    Female

Age               0.643 *   -0.219   0.237    -0.022
BMI                0.025    -0.315   0.103    0.542 *
PGY               0.613 *   -0.012   -0.104    0.136
Work Hours         0.195    -0.036   0.065     0.059
  /Week
Exercise           0.313    0.174    0.163    -0.086
  (min/week)
Sun Exposure      -0.118    0.171    -0.209   -0.036
  Score

                       BMD L1             BMD L2

Characteristics    Male     Female    Male    Female

Age                0.352    0.117    0.232    0.120
BMI               -0.134    0.268    -0.175   0.181
PGY                0.109    0.029    -0.093   0.122
Work Hours        0.525 *   -0.115   0.354    -0.024
  /Week
Exercise           0.227    -0.129   0.297    -0.071
  (min/week)
Sun Exposure      -0.195    -0.269   -0.218   -0.193
  Score

                      BMD L3            BMD L4

Characteristics    Male    Female    Male     Female

Age               0.176    0.006    0.059     -0.055
BMI               -0.228   0.129    -0.394    0.013
PGY               -0.109   0.142    -0.324    -0.014
Work Hours        0.282    -0.085   0.230     -0.046
  /Week
Exercise          0.395    -0.178   0.245     -0.115
  (min/week)
Sun Exposure      -0.239   -0.221   -0.104    -0.168
  Score
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Article Details
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Title Annotation:Original Research
Author:McConda, David B.; Boukhemis, Karim W.; Matthews, Leslie J.; Watkins, Colleen M.
Publication:West Virginia Medical Journal
Article Type:Report
Date:Jul 1, 2016
Words:3171
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