Bringing science to bear
Science and technology will never solve all of the problems associated with the inadequate food and care and the lack of health services and sanitation that lead to childhood malnutrition. But the successes stemming from breakthroughs being made and insights reached have stirred new hope for healthier, more productive lives for both children and adults. This section describes some of the crucial scientific advances that are helping to shape specific interventions to reduce malnutrition or that may do so in the future.
Some of this knowledge, such as the strengthening effect of vitamin A on the immune system, is well established; other knowledge is just emerging and is worth watching. Some of the new science is likely to accelerate efforts to reduce malnutrition, and at the same time generate new understanding of how reducing mal nutrition in childhood or during the prenatal period may lessen chronic disease in adulthood and the onerous public health burden it causes. There are also new tools to tackle the essential task of nutritional assessment and new ways that agricultural science can be brought to bear on the problem.
Nutritionally acquired immune deficiency
It is estimated that the immune systems of some 23 million people worldwide have been damaged by HIV.1 It is less well known that malnutrition impairs the immune systems of at least 100 million young children and several million pregnant women, none of them infected by HIV. But unlike the situation with AIDS, the 'cure' for immune deficiency due to malnutrition has been known for centuries: It is achieved by ensuring an adequate dietary intake containing all essential nutrients. Today, more is being learned about the specific role of individual nutrients in the functioning of the immune system, knowledge that will help in the design of interventions that can improve the situation in the near future. This knowledge also reinforces the importance of striv ing to ensure that everyone in the world has access to a diet that is adequate in both quality as well as quantity.
Photo: Over a million pre-school-age children suffer from vitamin A deficiency, which affects immune-system functioning. Vitamin A supplementation is estimated to lower a child's risk of dying by 23 per cent. In Bangladesh, a boy receives a vitamin A capsule.
Scientists have known for some time that malnutrition and infection are connected. A 1968 monograph by WHO, entitled 'Interactions of Nu tri tion and Infection', was one of the first comprehensive statements of some of these links.
The threat that vitamin A deficiency poses to the lives of young children has already been described. Within a few years, the scientific com munity went from calling the fact that vitamin A supplements could reduce child mortality "too good to be true" to calling it "too good not to be true."But the many ways vitamin A deficiency increases child deaths were not well understood until recently. Now the results of a dozen field studies, conducted in Brazil, Ghana, India, Indonesia, Nepal and elsewhere, indicate that supplementing the diets of children who are at risk of vitamin A deficiency can reduce deaths from diarrhoea. Four of the studies that focused on diarrhoea showed that deaths were reduced by 35-50 per cent. The vitamin can also halve the number of deaths due to measles2 (Fig. 11).
In Bangladesh, breastfed infants whose mothers were given a single oral high-dose supplement of vitamin A shortly after giving birth had sig nifi cantly fewer days of sickness because of respiratory infections and febrile illnesses during the first six months of life than did infants born to unsupplemented mothers from the same socio-economic group in the same area.3
Zinc is another micronutrient that has long been known to be essential for the growth and development of cells and for the functioning of the immune system. However, because zinc deficiency is extremely difficult to measure, little attention was paid until recently to the possibility that it might impair child health and development (Fig. 12).
Trials in Bangladesh, India and Indonesia have already shown reductions of about one third in the duration and severity of diarrhoea in children receiving zinc supplements and a median 12 per cent decline in the incidence of pneumonia.4 In these investigations, zinc supplements did the most good for those children who started out the most malnourished.
A study recently completed in Lima (Peru) found that the benefits of zinc supplementation on immunity can begin even before birth. Re searchers from the Johns Hopkins School of Public Health in Baltimore (US) and the Instituto de Investigaci¢n Nutricional in Lima have been adding zinc to the iron and folate supplements of pregnant women and test ing its impact on the health of their newborn children, including its effects on immune system activity. Initial analysis shows that antibody levels just after birth are higher in the children of zinc-supplemented mothers than in those receiving a placebo.
Zinc supplementation appears so effective in reducing the incidence of diarrhoea and pneumonia in poor countries that one scientist, Robert Black of Johns Hopkins University, has suggested that zinc supplements are as significant a public health intervention for diarrhoea reduction as improvements in water and sanitation. And major new research indicates that even the effects of malaria, a deadly enemy of both children and adults, may be lessened by zinc and vitamin A (Panel 18).
Iron deficiency can also damage the immunity of a growing child, impairing the body's ability to kill invading pathogens and leading to increased illness in iron-deficient populations.5 In studies in Egypt, anaemic children had longer and more severe episodes of diarrhoea than did their iron-fortified peers.
Basic science is now able to explain why these astonishing results occur. Thus far, zinc and vitamin A are the two micronutrients that have proved to be the most closely linked with the proper functioning of the body's front-line defences. These two micronutrients help maintain the physical barriers of skin and mucosa that prevent micro-organisms from invading the body, as well as enhancing the activity of leukocytes such as NK (natural killer) cells and mac ro phages - scavenger cells that engulf, then destroy, foreign pathogens such as bacteria throughout the body.
Equally important, low dietary consumption of zinc and vitamin A reduces the number and impairs the development and function of two types of B-cells - key players in 'acquired immunity'. These produce antibodies and T-cells that, in turn, are responsible for eliminating virus-infected host cells. They also produce biochemicals known as cytokines, which further promote B-cell and macrophage activity. At the same time, an adequate intake of zinc is now understood to be necessary in order for both vitamin A and iodine to do many of their vital jobs.
Nutrition and AIDS
The role of nutrition in preventing infection is now being investigated as one possible way to help reduce the transmission of AIDS. Vitamin A may form part of the arsenal needed to combat HIV, which is expected to infect between 4 million and 5 million children by early in the next century, most of them in sub-Saharan Africa. These children will mainly be infected by their mothers.
The routes of mother-to-child trans mission of HIV, also known as vertical transmission, are threefold: during pregnancy, during labour and delivery, and through breastfeeding.
Scientists have been exploring the possibility of reducing vertical transmission in all three routes since 1994. They have tried to block intrauterine transmission by giving women doses of the antiretroviral drug Zidovudine during pregnancy. The drug has been shown to reduce mother-to-child trans mission of HIV - but at hundreds of dollars per course, it is prohibitively expensive for most people in the devel oping world. Less expensive methods of antiretroviral therapy during pregnancy, such as administering Zido vudine for shorter periods or using cheaper drugs, are now being tested in Haiti, sub-Saharan Africa and South-East Asia.
Two other treatments during pregnancy are also under investigation. These involve either intravenous therapy with purified anti-HIV antibodies, or supplementation with vitamin A. In a 1994 study of HIV-infected women in Malawi, it was found that 32 per cent of those who were vitamin A deficient during pregnancy had passed HIV on to their infants. In contrast, only 7 per cent of HIV-infected women with sufficient levels of vitamin A did so. The study concluded that vitamin A-deficient women were thus four and a half times more likely to infect their children.6
Also, a 1995 study from Kenya reported that the concentration of HIV in breastmilk is higher in vitamin A-deficient mothers than in those with good vitamin A status. Another study, also from Kenya, has shown that HIV-positive women who are also vitamin A deficient were five times more likely than non-vitamin A-deficient women to shed HIV-infected cells in their reproductive tracts, a factor that may be an important determinant of both sexual and vertical transmission of AIDS. However, some experts have suggested that these results may have come about not because of the influence of vitamin A on HIV transmission, but because poor vitamin A status and high rates of infection occur together for other reasons.
Based on the findings of the first studies - and to demonstrate whether the connection between vitamin A and HIV transmission is causal - four clinical trials were begun recently to examine HIV transmission rates in women who have received vitamin A supplements during the second or third trimester of pregnancy. Results from these studies, conducted in Malawi, South Africa, Tanzania and Zimbabwe on a total of nearly 3,000 HIV-infected women, are expected soon.
In three separate trials of children hospitalized with measels -- one as early as 1932 -- deaths among children given high-dose vitamin A supplements were significantly lower than among children not supplemented. The consistent results suggest that a change in Vitamin A status can rapidly alter basic physiological funcitons to concerned with cellular repair and resistance to infection, thereby saving lives.
Source: Alfred Sommer and Keith West jr. Vitamin A Deficiency: Health, survival and vision.
Zinc's importance in ensuring normal growth and development is underlined in a 1986 study of Ecuadorian pre-schoolers with low zinc intake. The children were paired by sex, age and height: one in each pair was given a zinc supplement, the other a placebo. The resul;ts over 15 months showed a slow, steady gain in the supplemented children's height as compared with the non-supplemental group.
Source: H. Dirren et al 'Zinc supplementation and child growth in Ecuador, in Nutrient Regulation during pregnancy, lactation and infant growth.
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