Nutrition and development: other micronutrients' effect on growth and cognition.

Previous studies have provided strong evidence that protein-energy malnutrition, deficiencies of iron and iodine early on in life led to compromised growth and cognitive functions in young children. Recently, a growing body of knowledge indicated that other micronutrients also play a role in young child development. Severe as well as marginal vitamin A efficiency were shown to lead to an increased risk of morbidity and mortality in children. A meta-analysis of vitamin A intervention trials indicated an overall reduction of 23% in all-cause mortality rate. Delayed growth, especially stunting, was reported in children with clinical signs of vitamin A deficiency. In addition, deficiency of zinc, which is essential for DNA and protein synthesis, leads to growth failure and delayed secondary sexual maturation in man and animals. Preterm infants appear to benefit from zinc administration in terms of growth and development. Supplementation studies in infants and older children revealed that those who manifested overt zinc deficiency through either clinical or biochemical indicators showed an improvement in linear growth and occasionally, an increase in weight gain. Zinc may also play a major role in brain function based on strong evidence from experimental animals. Zinc deficiency gestation in mice, rats, rhesus monkeys caused impaired learning, reduced attention and poor memory in their offspring. Data in humans are few and inconclusive. With respect to brain function alone, other nutrients such as docosahexaenoic acid (DHA, 22:6 n-3 fatty acid) improve visual acuity and mental development in small-for-gestational-age infants, folate supplementation during pregnancy prevents neural tube defect in infants, selenium deficiency in animals affects activities of brain enzymes necessary for brain development and function. Although evidence is accumulating that micronutrients other than iron and iodine may be important for physical growth and brain development in young children, more well-controlled studies in humans are needed. Critical issues to be considered include: single vs multiple limiting nutrients, critical period of deficiency, responsive indicators and variables that may affect the results as environmental, psychological and social factors.