|SCN News, Number 09 - Focus on Micronutritients (ACC/SCN, 1993, 70 p.)|
|THE MICRONUTRIENT FORUM|
Lindsay H. Allen, presently at the Department of Nutrition, University of California, Davis, CA 95616-8669, was formerly at the Department of Nutritional Sciences, University of Connecticut, Storrs, CT 06269-4017
A perspective on the question of which micronutrients are needed, and how to deliver them, is inherently accepted by many participants in this forum. I believe it needs stating overtly. I can best illustrate my point by using pregnant and lactating women, and their infants and young children, as an example. We are all agreed that these are important target groups.
In this view of the problem, individuals in poor regions of the world obtain most of their dietary energy and protein from a few core, staple foods, which are usually cereals and legumes. Cereals and legumes have a low content of most vitamins, and while their mineral content may appear to be reasonable, bioavailability will be poor due to food constituents such as phytates and fiber. As households' resources improve, micronutrient-rich fruits and vegetables, and perhaps more importantly dairy and other animal products, are added to the staple. Thus, many households in poor areas are likely to be consuming adequate amounts of energy and protein from staple foods, but inadequate amounts of vitamins and bioavailable minerals. Micronutrient malnutrition, because of poor dietary quality, occurs even in the face of adequate energy and protein intakes. It will also, of course, occur where there is an inadequate quantity of food. It is much more widespread than protein-energy malnutrition.
When women subsist on such diets prior to pregnancy, they enter pregnancy with low stores and intakes of multiple micronutrients. Anemia develops frequently, but other nutrient deficiencies undoubtedly exist - it is just that we don't usually measure them. Fetal uptake and storage of many of those micronutrients will also be low so that the infant starts early life with low stores. To this is added the problem that the concentration of nutrients such as vitamin A, and water soluble vitamins, is likely to be suboptimal in breastmilk. There are good reasons for the present policy of advising breastfeeding for the first 6-12 months of life, but are we sure that infants so fed will receive adequate amounts of vitamins and minerals, if the diet of their mother is poor?
Within 3-4 months of birth, until about 21 months of age, growth-stunting is found almost universally in poor regions of the world. It is now recognised that, without doubt, children who are growth-stunted have functional impairments which are persistent, often to adulthood. Growth-stunting occurs even in infants who are completely breastfed. Some, but as presently understood, not all, of the stunting is often caused by diarrhea. The infant with diarrhea may have anorexia, with a negligible intake of both macro- and multiple micronutrients. It will also incur major fecal losses of zinc, copper, and fat soluble vitamins in severe cases, as well as other nutrients.
A recognised but as yet unquantified problem is that of undiagnosed, asymptomatic, subclinical infections by bacteria and parasites, often resulting in bacterial overgrowth. Micronutrients such as vitamin A, iron, carotene, vitamin B12 and others may be chronically malabsorbed for long periods of time starting within a few months of birth.
Then a suitable weaning food must be found. Frequently, home- or locally-prepared weaning foods are cereal-based and very low in micronutrients. Stunting continues, and anemia develops - along with further deficits in multiple micronutrients, most of which are not usually measured in prevalence studies. Programs that have focussed on the use of cereals during diarrhea at this age have undoubtedly saved many lives, but many probably don't replete micronutrient stores or improve longer-term growth.
Based on this scenario, how much will feeding more green leafy and yellow vegetables really help? Perhaps they will improve vitamin A status, if they are well-targeted (and in the case of leafy greens, well-disguised?). Will they improve iron status? There is little information on this; we may be adding oxalates and fiber as well as vitamin C. What about the other micronutrients likely to be deficient by this age?
In this Forum we have accepted that single or complementary (1-3 nutrient) supplements should be regarded as a short-term solution to severe deficiency situations. However, it is more than likely that a pregnant or lactating woman and her child will be deficient in more than 1-3 nutrients. Food-based strategies such as introducing green leafy vegetables and fruits will not fill the whold micronutrient gap. Moreover, such foods must be integrated into the usual diet, and intervention efforts must fit with what is normally available, consumed, and recommended.
It is important, therefore, to focus on food-based strategies that add as many micronutrients as possible to the diets of women and young children. This should be done as part of an overall plan that is integrated with: management of non-pregnant, and then pregnant and lactating women (who may benefit from most multi- vitamin mineral supplements as part of perinatal health care); breastfeeding policy vs the adequacy of micronutrients in breastmilk (how do lactating women and their infants benefit from micronutrient supplements?); the types of weaning foods that are available, used and recommended (can multiple micronutrients be added to local cereal-based gruels? Is powdered milk a possible medium?); and foods available to, and preferred and consumed by the young child.
The life stage approach to micronutrient interventions has the potential benefits of: i) targeting appropriate nutrients to individuals at nutritionally-vulnerable periods of their life; ii) complementing normal dietary practices; and iii) fitting into an integrated health care, nutrition delivery and education system. A similar approach can be used for other nutritionally-vulnerable population groups.