|Community-Based Longitudinal Nutrition and Health Studies : Classical Examples from Guatemala, Haiti and Mexico (International Nutrition Foundation for Developing Countries - INFDC, 1995, 184 pages)|
|3. The effect of malnutrition on human development|
The first impact of the supplementation interventions was on the mothers themselves. By the eighth month of pregnancy, the supplemented women consumed 20% more food (2,410 cal and 70.7 g protein vs 2,055 cal and 53.3 g protein) and had a higher pregnancy weight gain (+3.4 kg) than unsupplemented women. Among supplemented women, menstruation returned by 7.5+2.6 months postpartum, 6.2 months earlier than among unsupplemented women. An important consequence of this delayed return of menstruation was that the birth interval decreased from an average of 27 months to 19 months (A Chávez and Martinez, 1973). This effect cannot be attributed to decreased rates of breast-feeding, because all the supplemented women were breast-feeding en average of 7.3 times per day by the time that menses returned.
In this community, infants can be considered as extrauterine fetuses who depend on their mothers for survival during their first months of life. Then infants are fed almost exclusively on breast milk. Solid foods usually begin to make a critical nutritional contribution when the infant is beyond six to eight months of age.
The placenta is a very efficient organ for the transfer of nutrients from the mother to the fetus even when she is poorly nourished. However, this study demonstrates that maternal supplementation under these circumstances can improve birth weight. The newborns of supplemented mothers weighed 2,970 g at birth and were 180 g heavier than their counterparts in the unsupplemented group (A Chávez and Martínez, 1979c). This 6.5% increase m birth weight as trivial it might seem, IS Important for several reasons. First, this was the beginning of the anthropometric differences that persisted throughout life. Second, 39% (14/39) of the newborns in the unsupplemented group, but only 7.5% (3/40) of those in the supplemented group, were low birth weight (< 2.5 kg) infants. Third, food supplementation was also associated with increased total length, leg length, thorax circumference, ratio of head to thorax circumference, and ratio of leg to total length (A Chávez, 1978).
An important question is whether the decline in breast milk production even in the supplemented mothers is due to maternal malnutrition or is a natural phenomenon in the human species. The latter is a possibility, because all mammals follow a parabolic pattern of milk production, with a short incremental period and a long and progressive decremental stage. There is no reason for the human species to follow a different pattern of lactation. To respond to this question, the women who were supplemented during pregnancy continued to be supplemented during lactation. The total milk volumes plotted in Figure 1 show remarkable between-group differences. As with other mammals, breast milk production among supplemented women followed a parabolic pattern, peaking at four months, followed by a gentle decline.
The literature indicates that in developing countries, children begin to slow their growth at about three months of age. Therefore, it is important to consider the role of breast-feeding in the future of the child. A key finding from this study is that intake or production of breast milk in the unsupplemented group increased during the first eight weeks of lactation and fell thereafter (Martinez and Chávez, 1971). In the supplemented group it increased at least to 16 weeks. Unfortunately, milk volume measurements were not taken within the 8- to 1 6-week interval. However, by 16 weeks the milk volume had already decreased.
At eight weeks, the infants of unsupplemented mothers were consuming 32 ml per nursing episode, and by 16 weeks this figure decreased to 41 ml per episode. In Figure 2 a comparison of the breast milk intake per kilogram of body weight between the village children and Japanese children fed breast milk ad libitum with bottles indicates that the decrease in milk volume observed in the village after eight weeks is abnormal. This decline in breast milk production occurred despite the fact that children were breast-feeding about 13 times every 24 hours. Therefore, it is important to underscore that the decline in breast milk production is due to maternal supply and not infant demand. This decrease in breast milk production has important nutritional and developmental consequences for the child.
Chemical analysis of the milk samples indicated that the breast milk of unsupplemented women was not diluted according to the progressive pattern typical of other mammals. Unsupplemented women continued producing concentrated milk after their infants were eight weeks of age. By contrast, the milk of supplemented women was diluted beyond the expected range. Figure 3 includes the consumption of breast milk solids and shows that both groups of women secreted the nutrients following a pyramid-type pattern, although the peak is sharper among supplemented women. The peak for supplemented women was followed by a more gradual decline in the concentration of nutrients in breast milk after the infants were 3 months of age.
The between-group difference in the nutrient content of breast milk was 16% less in the supplemented group during the first eight months of life of the child. Although this difference does not seem large, it is important to underscore that it was greatest between 8 and 24 weeks. During this short period of time, the unsupplemented children ceased to be able to obtain all the breast milk that they demanded. To a certain extent, this also happened with the supplemented children, although in this case this phenomenon was observed at an older age and with a more gradual onset.
The decline in breast milk consumption by the children of poorly nourished mothers that begins at two to three months of age is the first insult that leads to malnutrition during early childhood. This situation could be easily corrected by introducing complementary foods available in the household by three months of age as required to maintain weight gain.
Figure 4 shows the between-group differences in energy intake. The deficiency in energy intake in the unsupplemented group begins at 12 weeks and is not corrected later. By eight months of age, the between-group differences in nutritional status are not readily apparent to the observer, i.e., the unsupplemented children were not obviously malnourished. However, more detailed analysis of their nutritional status shows some impairments. Photographs confirmed that supplemented and unsupplemented mother-child pairs had different attitudes and different characteristics of the skin, adipose and muscular tissues (Chávez and Martínez, 1982).
By eight months, the unsupplemented children had already been exposed to two nutritional insults. The first occurred in utero due to a deficient transfer of nutrients across the placenta. The second occurred at about three months of age due to a decrease in maternal breast milk production. In view of these insults, why were there so few clinical manifestations? First, breast-feeding allows infants to recover partially from the in utero insult. During the first three months of life, the infant has access to an abundant supply of milk and grows at a very fast rate. Second, biological mechanisms protect the child against nutritional insults. This is illustrated by the fact that the child can maintain lean tissue at the expense of his fat reserves. Another coping mechanism is a reduction in physical activity. This hidden malnutrition is likely to have negative long-term consequences for the future development of the child, even though dramatic effects are not evident by eight months of age.
As shown in Figure 5, the between-group difference in weight is small at eight months. Furthermore, it is still not possible to detect significant differences in the infants' utilization of nutrients, physical activity, or behavior. However, some indicators show consistent differences. Perhaps the most pronounced differences can be seen in neurological development both at birth and during early infancy (Rodríguez et al., 1979). By eight months, the unsupplemented child had less reflex control and poorer psychomotor development (A Chávez et al., 1975). There were also some behavioral differences. Unsupplemented children cried more, played less, and had less than optimal family interaction (A Chávez and Martínez, 1975).
The fact that there were no obvious clinical manifestations of malnutrition up to eight months of age has led some people to recommend exclusive breast-feeding for a minimum of six months. However, this study does not support this argument, since the breast milk supply begins to decline by three months, and small developmental, biological, and behavioral deficits begin to appear. These deficits become larger as the child grows older in a socioeconomically deprived environment.
In short, on the one hand, children who reach eight months of age with acceptable growth, such as weighing more than 8 kg, will be more likely to crawl, to demand attention, and to have better immunological defenses. On the other hand, a child who reaches eight months under adverse conditions, grows less well, has a poor appetite and low levels of physical activity and social interaction and is likely to become more malnourished.