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Statement on natural food sources of vitamin A and provitamin A
IUNS Committee II/6
The International Union of Nutritional Sciences (IUNS) Committee II/6 on Nutrition and Anthropology has developed the following statement on the basis of the two preceding reviews.
Vitamin A deficiency is highly prevalent in developing regions: recent data indicate that the magnitude and severity of the problem are more extensive than originally assessed. Temporary measures to treat and control vitamin A deficiency, notably the periodic massive dosage approach, are still being actively promoted for their value in reducing child mortality [1]. Community trials in India [2], Indonesia [3], and Nepal [l] strongly support the association of vitamin A supplementation and reduced preschool child mortality. Vitamin A supplements have an important role in child survival, particularly in reducing mortality associated with infectious disease. However, the continued use of synthetic vitamin A supplements may be creating a complacency relative to the long-term goals for improved dietary intake of vitamin A-rich foods [4]. The benefits of promoting natural food sources of vitamin A are that change will be more sustainable and economically sound.
Improving vitamin A status through dietary modifications requires accurate food composition data for the identification of vitamin A-rich foods, assessment of dietary intake of vitamin A, and recommendations on cooking processes that minimize losses of preformed vitamin A and provitamin A. The widespread use of high performance liquid chromatography (HPLC) has created an expanding database of nutrient values, including information on isomers associated with the cooking process that reduce the biological availability of vitamin A. However, the food composition data on vitamin A-rich foods are far from complete. In developing regions HPLC is often not a viable analytical technique, and local foods are often analysed using outdated techniques, or nutrient values are extrapolated from analysis of foods from different geographical regions. To date, few food composition tables have been updated to incorporate the expanding data on vitamin A, including identification and quantification of different carotenoids and isomers. Given the large variation in the nutrient content of vitamin A-rich foods and inadequacies in the food composition literature, there has been a shift towards the classification of foods based on their relative contribution to vitamin A intake [5]. By reducing vitamin A activity into a score of low, medium, and high based on retinol equivalents (RE), a simplified dietary analysis can possibly be used in some situations to estimate dietary intake of vitamin A.
Reaching the goal of improving vitamin A status through dietary modifications involves more than an increased intake of vitamin A-rich foods. For example, at least 5 g per day of dietary fat is recommended in a child's diet to optimize the absorption and utilization of preformed vitamin A and provitamin A [6]. Other nutrients that facilitate the utilization of vitamin A include protein, vitamin E, and zinc. The nutrient density of the diet is also an issue in formulating dietary recommendations for groups at risk of developing vitamin A deficiency, notably preschool children. The intake of vitamin A through natural sources may be limited by the quantity and the frequency of food consumption required to meet the individual's requirements not only for vitamin A but also for other nutrients such as protein and energy. Given the well-documented interrelationships between vitamin A status and infectious disease, dietary modifications may be compromised by repeated occurrences of infection. Conversely, increased dietary intake of vitamin A from natural food sources may improve the individual's resistance to infection, although the mechanisms have yet to be clarified. Therefore a dietary approach to the vitamin A deficiency problem needs to incorporate modifications in the intake of other foods when necessary and to promote health measures that reduce infectious diseases.
Ecological, economic, and cultural factors act differentially on the intake of vitamin A-rich foods. Identification of food items rich in vitamin A activity will not improve a vitamin A deficiency problem if the foods are not available locally or are economically inaccessible. Furthermore, a single food item is subject to very different interpretations in different cultural settings, and inclusion or exclusion of a natural food rich in vitamin A can be determined by beliefs and attitudes dictated by multiple cultural factors such as religion, alterations in physiological status, and gender and age discrimination, to name a few. Moreover, intracultural variation in cultural classifications is considerable. The evidence highlights the need for locally relevant data and the active involvement of community members in the design of programmes for the improvement of vitamin A status through dietary modification. This is supported by the few available evaluations of programmes intended to increase the consumption of natural foods rich in vitamin A activity. It becomes increasingly clear that preliminary local community data on the availability of foods: their economic value; consumption patterns; attitudes, beliefs, and values about food; feeding behaviours; and existing vitamin A deficiency can be used to create locally effective programmes for the prevention of vitamin A deficiency and improved health that will be sustainable over the long term.
Social marketing techniques, nutrition education, and promotion of gardening activity all have potential for modifying dietary practices that affect vitamin A status. The few published examples of programmes that have created sustainable dietary modifications to treat and control the problem of vitamin A deficiency indicate that substantial efforts are required in community-based research if the long-term goals of dietary modifications to prevent vitamin A deficiency are to be achieved.
Acknowledgements
We gratefully acknowledge the contributions of Dr. Gretel Pelto and Dr. Richard Young of the Committee on Nutrition and Anthropology, International Union of Nutritional Sciences, for their contributions to the preparation of the preceding committee statement and supporting manuscripts. Special thanks also to Lauren Blum, Dr. C. Gopalan, Dr. Mahshid Lotfi, Dr. P. Pushpamma, Suttilak Smitasiri, and Dr. S. Wahba. Financial support from the Food and Nutrition Programme for Human and Social Development of the United Nations University made this work possible.
Harriet V. Kuhnlein and Isabel Nieves
Cochairpersons, Committee II/6
International Union of Nutritional Sciences
References