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Discussion

Our results confirm the hypothesis that the positive effects of supplementation on growth at 3 y of age persist at adolescence, although slightly attenuated. Children supplemented with Atole (high-protein/highenergy drink) in their first 3 y of life were taller, heavier and had higher FFMs at adolescence than those supplemented with Fresco (low-energy/no-protein drink). The study also showed that differences between the Atole and Fresco groups at adolescence were largely explained by the effect of supplementation on body size at 3 y of age. This was demonstrated by statistical analyses that showed that Atole and Fresco differences at adolescence disappeared when body size at 3 y of age was included in the models.

Differences between Atole and Fresco were larger in females than in males for all outcomes and at both 3 y of age and adolescence. Differences in favor of females were striking, particularly in FFM, with differences being almost three times larger in females than in males. An intriguing finding was that Atole versus Fresco differences in FFM in females were not totally explained by height at adolescence, suggesting a long-term effect of early supplementation on FFM, independent of the effect on height.

Differences at adolescence relative to those observed at 3 y of age were larger for weight than for height for both genders. Differences in weight were explained mainly by differences in height (i.e., differences in weight disappeared after controlling for height) and for this reason, the remainder of the discussion focuses on height.

The differential response to supplementation between males and females, both at 3 y of age and at adolescence is difficult to explain. It appears that this gender difference at adolescence was mainly due to differences already existing at 3 y of age. Differences between Atole and Fresco in females at 3 y of age were greater by 0.9 cm compared with those found in males. Between 3 y of age and adolescence, both males and females in Fresco villages grew ~0.8 cm more than children in Atole villages (see below). This increased rate of growth among Fresco children resulted in attenuated differences between Atole and Fresco at adolescence in both genders. In males, however, the smaller magnitude of the difference at 3 y of age, combined with larger standard errors at adolescence, resulted in differences between Atole and Fresco at adolescence that were no longer statistically significant. Larger standard errors in adolescent males are thought to be due to variations in maturity. Although a large proportion of females had reached maturity at the time of the study, this was not the case for males. Although skeletal age was used in the analyses to control for maturation, extreme variations in height associated with differences in maturity could not be completely controlled for.

We have explored possible reasons for the smaller magnitude of difference between Atole and Fresco villages observed in males at 3 y of age. Examination of results within village pairs indicates that differences in favor of Atole in the pair of large villages were statistically significant in males (Table 6) and similar to differences seen in females. Also, differences between Atole and Fresco in males in the large villages remained statistically significant at adolescence. In contrast, differences were less and not statistically significant in males in the small villages either at 3 y (P = 0.28) or at adolescence (P = 0.32). We have no adequate explanation for the lack of a supplement effect in males in the small pair of villages.

TABLE 6 Adjusted length/height (cm) of Atole and Fresco males by village size

* P<0.05 (two-tailed).

¹ All means were adjusted for dietary intake, percent time with diarrhea socioeconomic status, maternal height and maturation (in the case of adolescence only). Values are means ± SE.

² Atole minus Fresco.

Differences in attained height at adolescence in favor of Atole villages disappeared after controlling for length at 3 y of age. This was expected because most of the growth deficit observed in adolescents and adults in this population occurs during the first 3 y of life. Growth after 3 y in this population is generally adequate and may even be greater than that observed in Mexican-Americans (Martorell et al. 1995b). In our study, children in the Fresco villages grew slightly more from 3 y of age to follow-up than children in Atole villages. (72.1 versus 71.3 cm in Fresco and Atole males respectively and 65.0 cm and 64.2 cm, respectively, in females; from data in Table 3). This small difference in growth may be the result of accelerating effects of the Atole on bone maturation in the preschool period (Martorell et al. 1979), which would provide children in the Fresco villages with a greater growth potential after 3 y of age. Another possible explanation for the above is better environmental conditions during school age and adolescence in Fresco villages. Our data suggest that environmental factors may have had an effect on growth from 3 y of age to adolescence (see Appendices 1-3). In females, socio economic status was a statistically significant determinant of height at adolescence and the effect continued to be significant after controlling for length at 3 y of age. This suggests a positive effect of socioeconomic factors on growth in sleight after 3 y of age in females.

A number of variables besides supplementation were statistically significant in the models (see Appendices 1-3). In addition to maturation, maternal height was an important determinant of height and weight at 3 y of age and at adolescence in both sexes. Moreover, maternal height was also a statistically significant predictor of growth at adolescence once size at 3 y of age was controlled for, indicating an effect on growth after 3 y of age. As mentioned earlier, maternal height is thought to be a proxy for both genetic potential and environmental factors. Dietary intake and diarrhea during the first 3 y of life were statistically significant predictors of size at adolescence in some models but were not significant when size at 3 y of age was controlled for. These results suggest that, although the effects of diarrhea and dietary intake on growth take place during the first 3 y of age, the effects persist into adolescence.

In summary, the results show long-lasting effects of supplementation during the first 3 y of life on body size and composition at adolescence. Although differences in height at adolescence were reduced in magnitude relative to those found at 3 y of age, the degree of reduction was similar in both males and females, and the results at adolescence did not change substantially relative to results at 3 y of age. In weight, differences were increased at adolescence relative to 3 y of age.

In this population, the first 3 y of life is the period of maximum growth retardation, whereas growth thereafter may be adequate (Martorell et al. 1995). Our results show that investment s in nutrition during early childhood have effects on growth that persist into adulthood. Greater height and FFM in turn may have effects on reproductive performance in females, notably on fetal growth, and consequently on the health and survival of the next generation. Effects on body size in adolescent males, through its association with greater work capacity (Haas et al. 1995), may in turn be associated with increased future earning power.

APPENDIX 1 Multiple Regression models for length at 3 y and height at adolescence

Supplement type: Atole = 1, Fresco = 0.

Dietary intake: at or above gender specific median = 1, below gender specific median = 0.

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