Do we need more food fortification?

The science of nutrition went through a tremendous phase of expansion in the first half of the twentieth century with the discovery that some diseases could be treated and prevented by ingesting sufficient amounts of bioactive substances--vitamins and minerals--largely derived from food. This work encouraged a great effort to determine essential nutrient requirements and to use this knowledge to establish recommended nutrient intakes that would provide direction to eliminate nutrient deficiency diseases. So successful was the work of nutritional scientists that nutrient deficiencies were thought to have been largely eliminated in economically developed countries by the second half of the last century. Over the last two decades research focus has shifted emphasis from essential nutrient requirements to learning whether intakes of essential nutrients higher than those needed to prevent deficiency diseases can reduce the risk of chronic disease such as cancer and heart disease, improve cognition, or enhance immune function. Not only have these new areas of research engaged traditional nutritional scientists working in the public and academic arenas but industry has become an active and important participant by providing research funding opportunities for producing value added novel and functional foods. So prominent has this area of research become that the importance of nutrients in preventing classic nutrient insufficiencies may have been overlooked. It is perhaps not surprising, therefore, that there is an accumulating body of evidence that nutritional deficiencies, far from being defeated, are once again emerging as a public health concern.

Of recent note are the results of the 2002 National Children's Nutrition Survey (CNS02) in New Zealand indicating that mild iodine deficiency exists among school-aged children (1). Median urinary iodine concentration was 66 [micro]/L and 28% of children had a urinary iodine concentration below 50 [micro]/L. Both of these conditions meet the International Council for the Control of Iodine Deficiency Disorders definition of mild iodine deficiency: median urinary iodine between 50-100 [micro]/L and more than 20% of population with values less than 50 [micro]/L. These results, based on a large representative sample of New Zealand children (n = 1800), are not surprising because they confirm results of smaller representative surveys of school children in Dunedin and Wellington (2), as well as Melbourne (3) and Tasmania (4).

Reports on Vitamin D are still pending final approval from the New Zealand Ministry of Health. It has been assumed for some time that dietary intakes of vitamin D among Australians and New Zealanders were of little concern because sun exposure ensured adequate cutaneous synthesis of the vitamin. This assumption has been drawn into question by studies indicating that vitamin D status is low--assessed using serum 25 hydroxyvitamin D concentrations--in small volunteer samples of several Australian population groups such as the elderly, veiled women, as well as children and adolescents (5). More recently, results from the CNS02 showed that vitamin D status of New Zealand children is poor. The prevalence of insufficiency, defined as a serum 25 hydroxyvitamin D concentration less than 37.5 nmol/L, was 31% and the prevalence of deficiency (< 17.5 nmol/L) was 4%. There were 14% of Pacific females, 11 to 14 years, who had serum 25 hydroxyvitamin D concentration indicative of deficiency. Preliminary results from the National Nutrition Survey 1997 of New Zealanders 15 years or older suggests equally low serum concentrations of 25 hydroxyvitamin D. The high prevalence of insufficient vitamin D concentrations raises immediate concerns about the potential public health consequences of low vitamin D status and the need to devise strategies to improve this. Other well-described examples of nutrient deficiencies include iron in women and vitamin [B.sub.12] in the elderly and results from the CNS02 suggest zinc may also be of concern.

Unfortunately, the quality of information about the nutritional status of Australians lags behind that of New Zealanders. The reason for this stems largely from the fact that biological samples were collected from participants in the last two New Zealand nutrition surveys (1.6) but were not in the Australian National Nutrition Survey 1995 (7). Determining the extent of nutrient deficiencies using biochemical markers of nutritional status is far superior to relying solely on the results of dietary assessment. Dietary assessment without biochemical indicators is of minimal value in assessing the iodine and vitamin D status of a population.

The presence of mild iodine deficiency and the high prevalence of insufficient vitamin D concentrations raises immediate concerns about the potential public health consequences of the compromised nutritional status of a significant proportion of the New Zealand and probably the Australian populations. It also demands an immediate response to considering and devising strategies to improve the iodine and vitamin D status of each population. Food fortification must surely rank as the strategy most likely to succeed. It seems fortuitous that the Food Regulation Standing Committee is currently considering policy guidelines for the fortification of the Food Supply with Vitamins and Minerals (http://www.nzfsa.govt.nz/policylaw/consultation/archive/fortification-of-the-food-supply/index.htm). Should these be adopted, food standards will need to be developed and these will guide the method of any mandatory or voluntary fortification strategies.

There is a sense that new discoveries are waiting to be translated into fortification strategies that will benefit public health by reducing the burden of chronic disease. There have been many instances of observational epidemiological evidence linking increased intakes or high blood levels of a vitamin or mineral with decreased risk of cancer or heart disease (8-10). Unfortunately, with few exceptions the results of randomised controlled trials of vitamin and mineral supplements for the prevention of these diseases have been rather disappointing (11-12). The evidence that vitamin and mineral deficiencies exist in our populations does not necessitate an abandonment of the 'health optimisation' concept rather it demands a refocusing of attention onto the essentials of maintaining adequate nutritional status of the population through provision of adequate vitamin and mineral intakes.

The recent discovery that our food supply does not provide all the necessary vitamins and minerals to prevent deficiency (e.g. iodine and vitamin D) will challenge many nutritionists and dietitians who have long argued that a varied diet provides all the nutrient requirements we need. Clearly, a re-evaluation of this assumption is needed. Food fortification is not a panacea. The fact that its history of use to improve nutritional status contains examples with greatly varying degrees of success, demands that the appropriate modelling, testing, and monitoring steps be carefully and thoroughly undertaken.

References

1. Parnell W, Scragg R, Wilson N, Schaaf D, Fitzgerald E. NZ Food NZ children: Key results of the 2002 National Children's Nutrition Survey, Wellington: Ministry of Health; 2003.

2. Skeaff SA, Thomson CD, Gibson RS. Mild iodine deficiency in a sample of New Zealand schoolchildren. Eur J Clin Nutr 2002;65:1169-75.

3. McDonnell CM, Harris M, Zacharin MR. Iodine deficiency and goitre in schoolchildren in Melbourne, 2001. Med J Aust 2003;178:159-62.

4. Guttikonda K, Travers CA, Lewis PR, Boyages S. Iodine deficiency in urban primary school children: a cross-sectional analysis. Med J Aust 2003;179:346-8.

5. Nowson CA, Diamond TH, Pasco JA, Mason RS, Sambrook PN, Eisman JA. Vitamin D in Australia. Issues and recommendations. Aust Fam Physician 2004;33:133-8.

6. Russell DG, Parnell WR, Wilson NC. NZ Food: NZ People. Key results of the 1997 National Nutrition Survey. Wellington: Ministry of Health; 1997.

7. Australian Bureau of Statistics. National Nutrition Survey. Nutrient Intakes and Physical Measurements. Canberra: Australian Bureau of Statistics; 1998.

8. Stampfer MJ, Hennekens CH, Manson JE, Colditz GA, Rosner B, Willett WC. Vitamin E consumption and the risk of coronary disease in women. N Engl J Med 1993;328:1444-9.

9. van Poppel G, Goldbohm RA. Epidemiologic evidence of betacarotene and cancer prevention. Am J Clin Nutr 1995;62:1393S-1402S.

10. Boushey CJ. A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. Probable benefits of increasing folic acid intakes. JAMA 1995;274:1049-57.

11. Verhoef P, Katan MB. A healthy lifestyle lowers homocysteine, but should we care? Am J Clin Nutr 2004;79:713-4.

12. Vivekananthan DP, Penn MS, Sapp SK, Hsu A, Topol EJ. Use of antioxidant vitamins for the prevention of cardiovascular disease: meta-analysis of randomised trials. Lancet 2003;361:2017-23.

Murray Skeaff PhD

Tim Green PhD

Department of Human Nutrition

University of Otago

New Zealand