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The mean age at menarche in subjects exposed to Atole, a high energy and high protein supplement was 13.74 y, nearly identical to the value of 13.75 y found in subjects e xposed to Fresco, a low energy, no protein supplement. The mean age at menarche for immigrants (n = 144), subjects not exposed to either supplement, was 13.55 1.20 y. Most of these immigrants married village men and are likely to be of similar SES and education as the sample of women exposed to the supplements. The fact that immigrants, in effect a control group, reached menarche at about the same age as Atole and Fresco women provides additional evidence that supplementation did not influence age at menarche.

Some reports of age at menarche in Guatemala are available, Sabharwal et al. (1966) reported a mean age at menarche of 12.8 y for 230 upper socioeconomic urban girls and 14.5 y for 218 lower socioeconomic rural Mayan Indian girls. Notably, a later recalculation using probit analysis estimated those values to be 13.3 and 15.1 y, respectively (Eveleth and Tanner, 1976). Delgado et al. (1984) reported that the median age of menarche of girls living under poor conditions on 12 coffee plantations located in Suchitepequez, Quezaltenango and Alta Verapaz was 14.81 y. The average values in the present study are only slightly later than found in the well-to-do urban sample (i.e., 13.71 vs. 13.3 y). In our study, women with higher SES (1.0 SD above the mean) reached menarche ~0.30 y earlier than those of lower SES (1.0 SD below the mean). Thus, women of higher SES in our sample had nearly identical mean age at menarche as the urban sample, if the recomputed value of 13.3 y is used.

Age at menarche showed a tendency to decline over time in Atole and Fresco groups as well as in immi grants. The observed rate of decline is slightly greater (0.50 y per decade) reported in other studies. It may be that this value is an overestimation because 13 cases had not reached menarche by the end of data collection, artificially depressing the mean age at menarche. To test this theory, we assumed conservatively that all 13 subjects were "late" maturers and assigned them a value of 17.58 y, the overall mean plus 3 SD. Inclusion of these 13 subjects using assigned values did not alter the basic observation that menarche declined over time; however, the rate of decline was reduced to 0.39 y per decade.

Comparable data on changes in age at menarche over time in other Latin American populations are limited. A study from Chile (Rona 1975) found that the rate of decline was, on average, 0.29 y per decade between 1940 and 1970. Using recall data of women age 20-59 y, Malina et al. (l983) found no decline in age at menarche for girls in Oaxaca, Mexico.

A differential rate of decline in age at menarche according to SES has been reported (Low et al. 1982, Padro 1984, Rona 1975, Singh and Malhotra 1988). In Chile, Rona (1975) found that the rate of decline from 1940 to 1970 was greater in the middle classes than in the upper classes. In Madrid and a nearby suburb, Padro (1984) reported that menarche declined from 1935 and 1965 by 0.34 y per decade in the upper classes compared with 0.43 y in the lower classes. Similarly, among Malaysian Chinese, Indian and Malay females, ages at menarche fell on average 0.27 y per decade for women born between 1926 and 1961, with a greater decline observed in those raised in poorer households; about one half of the decline was accounted for by improved SES over the period studied (Tan-Boom et al. l983). In summary, the secular trend in age at menarche is often greater in lower compared with higher SES groups.

In the present study, an interaction between year of birth and SES was not statistically significant in either Model 1 or 2, suggesting that the rate of decline in age at menarche was not influenced by SES. It may be that the variance in SES in our study is too small to pick up an interaction; in other studies (e.g., Padro 1984, Rona 1975), the socioeconomic differences were more extreme.

In the present study, statistically significant interactive effects of supplementation with SES and year of birth on menarche were found. At high SES (1.0 SD above the mean), subjects exposed to Atole reached menarche 0.90 mo later than those exposed to Fresco. At low SES,(1.0 SD below the mean) subjects exposed to Atole reached menarche 0.72 mo earlier than those exposed to Fresco. The strength of the interaction with year of birth can be ascertained from Figure 1. Reasonable and plausible explanations for these interactions have not been found despite considerable effort. In view of the moderate to small magnitude of the interactive effects and, more importantly, due to the lack of plausible explanations, these results are disregarded in drawing up the main conclusion of the analyses.

Intake of Atole was associated positively with childhood maturity as measured by the number of ossification centers present in subjects<3 y of age (Martorell et al. 1979). Limiting the analysis of menarche to subjects exposed to supplement from birth to 3 y of age, the mean age at menarche (years) is exactly the same for both groups: 13.78 1.26 for Atole (n = 178) and 13.78 1.27 for Fresco (n = 167), respectively. This suggests that the previously demonstrated impact of supplementation on maturity during early childhood did not continue into early adulthood.

The relationship between supplementation and skeletal age in adolescence in our study population has been investigated by Pickett et al. (1995) using the Radius-Ulna Short bones (RlJS) option of the Tanner White house-2 (TW2) method (Tanner et al. 1983). This method yields skeletal ages and relative maturation can be assessed by comparisons to chronological ages, with British data used as the reference population. Skeletal maturation was significantly delayed (P<0.05) in the combined sample only in boys 11-14 y of age (by 1.2 y); in girls 11-14 years, values were slightly accelerated (+0.23 y) with respect to the reference. Many girls 14- 18 y had reached maturity and a reliable estimate of maturational delay could not be made; in boys 14-18 y, there was a delay of 0.16 y, but this was not statistically significant. There were no significant differences (P<0.05) in skeletal ages between Atole and Fresco subjects except in females 11-14 y of age, with those exposed to Atole being 0.4 y more advanced; however, these differences ceased to be statistically significant after controlling for SES. These findings corroborate those on menarche; there is no evidence of marked de lays in maturation in the population and exposure to Atole has little or no impact.

There is the possibility that supplement intake in children older than 7 y of age may have attenuated Atole and Fresco differences in maturity. Very little Fresco was consumed in the first 3 y of life; however, by 5 - 7 y, consumption of Fresco was greater than that of Atole in terms of volume, such that high levels of energy and micronutrients were consumed at these ages in both Atole and Fresco villages. It is possible that these high levels of consumption persisted late into adolescence. This is unlikely, however, because former field workers recall that it was mostly women and the target children under 7 y of age who frequented the supplement centers. Nonetheless, the possibility should be entertained. Assuming that intakes of both Fresco and Atole remained high after y of age and that these influenced age at menarche, one would have expected lower ages at menarche in the study sample compared with immigrants, but such was not the case.

The association between energy intakes and age at menarche has been examined previously, mostly in industrialized countries (Kissinger and Sanchez 1987, Maclure al. 1991, Meyer et al. 1990), Moisan et al. (1990). In these studies, dietary intakes in the 1-3 y before menarche were examined; none looked at intakes during childhood as we have done. Results from these studies suggest that energy intakes in the years immediately before menarche have little or no relation to age at menarche, consistent with our own findings.

A limitation with this study is that the data on age at menarche were collected retrospectively. There is no reason to believe, however, that responses were biased either toward younger or older ages or that subjects of one supplement type responded differently from the other. Limiting the analyses to subjects who recalled their age at menarche within 3 mo in the two surveys, the values were 13.78 1.32 y (n = 111) and 13.56 1.25 (n = 105) y for Atole and Fresco villages, respectively.

To our knowledge, no previous investigation of the effects of nutritional supplementation on menarche has been reported. Our study found that mean age at menarche was similar for subjects who received either a high energy and high protein supplement (Atole) or a low energy, no protein supplement (Fresco). No differences between supplement type were found when analyses were limited to those who accurately recalled their age at menarche or to those subjects who were exposed to supplements in the first 3 y of age. In addition, immigrants of similar SES background who were not exposed to any supplement had a similar mean age at menarche. Therefore, we conclude that nutritional supplementation did not have an affect on age at menarche in the present study. Nonetheless, the fact that both SES and year of birth were found to be associated with age at Menarche indicates that menarche is subject to general environmental, and possibly nutritional, influences.

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