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Age at menarche and nutritional supplementation(¹,²)

AWAL D. KHAN,* DIRE G. SCHROEDER,† REYNALDO MARTORELL³** ‡ AND JUAN A. RIVERA**

*Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853-6301, †Department of International Health, The Rollins School of Public Health of Emory University, Atlanta, GA 30322, and *Centro de Investigaciones en Salud Pública, Instituto Nacional de Salud Publica, 62508 Cuernavaca, Morelos, Mexico

¹ Published as a supplement to The Journal of Nutrition. Guest editors for this supplement publication were Reynaldo Martorell, The Rollins School of Public Health of Emory University, Atlanta, GA and Nevin Scrimshaw, The United Nations University, Boston, MA.

² Supported by National Institute of Health grant HD 22440 and grants from the International Center for Research on Women (LIC-75/03) and the Thrasher Research Fund (#2805-5).

³ To whom correspondence should be addressed: Department of International Health, The Rollins School of Public Health of Emory University, 1518 Clifton Road, N.E., Atlanta, GA 30322.

Materials and methods
Results
Discussion
Literature cited

Age at menarche occurs earlier than it once did in many parts of the world, especially in Europe and North America (Eveleth 1986, Laslett 1985, Tanner 1973, Wyshak and Frisch 1982). In these regions, age at menarche declined at the rate of ~0.3 y per decade till it stabilized at ~ 13 y (Eveleth 1986, Poppleton and Brown 1966, Sandler et al. 1984, Tanner 1981). This decline, also seen in some developing countries, has been attributed to improvements in nutrition and health (Bielicki et al. 1986, Eveleth 1986, Hulanicka and Waliszko 1991, Laslett 1985, Low et al. 1982, Malina et al. 1977, Rona 1975, Singh and Malhotra 1988). Similarly, the fact that menarche occurs later in the poorer social classes compared with the well to-do in developing countries has been ascribed to disparities in nutrition and health (Charzewska et al. 1976, Chowdhury et al. 1977, Eveleth and Tanner 1990, Foster et al.1986, Gandotra and Das 1981, Rana et al. 1986, Tan-Boom et al.1983, Uche and Okorafor 1979).

Improvements in the quality of life during early childhood can result in earlier menarche. Indian and Bangladeshi girls adopted between 1 mo and 11 y of age (mean age 3.7 y) by Swedish families experienced earlier pubertal growth and menarche compared with Swedish and affluent Indian girls (Adolfsson and Westphal 1981, Proos et al. l 991 a, Proos et al. 1991 b). The timing of adoption had a signincant but unexpected influence on menarche; girls who were adopted after 3 y of age reached menarche ~9 mo earlier than those adopted between birth and 3 y of age. Catch-up growth occurred in all age cohorts shortly upon arrival but in older girls it may have triggered endocrinological responses and early puberty, whereas in younger girls it did not. However, age at menarche still occurred earlier in girls adopted before 3 y of age than it did in subjects reared in India. The corresponding values were 11.9 and 11.1 y for girls adopted before and after 3 y of age, respectively, compared with 13.7 y for urban and 14.4 y for rural Indian-reared girls.

These findings suggest that broad improvements in nutrition and in living standards are determinants of age at menarche. However, no study has examined the impact of community-based nutrition interventions during childhood on age at menarche. The aim of this study is to test the hypothesis that women who were exposed to a high energy and high protein supplement during childhood reached menarche earlier than those exposed to a low energy, no protein supplement.

Materials and methods

Data source and study sample. Data for this study are derived from a longitudinal nutritional intervention study carried out between 1969 and 1977 in Guatemala and from resurveys of the study subjects starting in 1991 (Martorell et al. 1995). The community-based nutrition intervention study was conducted by the Institute of Nutrition of Central America and Panama (INCAP) and was designed to test whether improved nutrition in early childhood results in better growth and development. Four villages stratified by size (two large and two small) were selected randomly to receive either a high energy, high protein supplement called Atole or a low energy, no protein one called Fresco. Atole contained 163 kcal (682 kJ) and 11.5 g protein per cup or 180 mL, whereas the Fresco had 59 kcal (247 kJ) per 180 mL and no protein. Both supplements contained equal amounts of thiamin (1.1 mg), riboflavin (1.5 mg), niacin (18.5 mg), iron (5.0 ma) and vitamin A (1.2 mg). In addition, the Fresco contained a flavoring agent and Atole contained a small amount of fat (0.7 g), calcium (0.4 g) and phosphorus (0.3 g). More details about the intervention study are given elsewhere (Martorell et al. 1995).

Reproductive histories were collected in 976 women between 15 and 30 y of age in two survey rounds in 1991 and 1992. The target sample for these surveys was all women residents born between January 1962 and August 1977 (i.e., the range in birth dates of the subjects who participated in the longitudinal study). Women who were former participants (n = 832) of the longitudinal study are emphasized in this analysis. They represent 72% of the original sample with available supplementation records. Immigrants and subjects who were born after August 1977 (n = 144) are excluded from the main analyses but are used as a comparison group in some analyses. Immigrants were those who moved to the study villages because of marriage or the establishment of a new family after 1977 when the intervention ended.

Exposure to nutritional supplementation. Participation in the intervention study was voluntary and open to all members of the community. Intakes of supplement were measured daily for children until 7 y of age, pregnant women and women in the first 24 mo postpartum (Martorell et al. 1995). A limitation of the study is that supplement consumption was not recorded for other subjects. In addition, exposure to supplementation had variable entry ages and durations. For example, if a participant was 5 y old in 1969 when the intervention began, supplement intakes from 5 to 7 y were measured. She then could have received supplement for 7 more years until 1977 when the study ended, but these intakes were not measured.

Age at menarche. Menarche data were gathered during two rounds in 1991 and 1992. During each round, subjects were asked whether they had reached menarche. Those who answered affirmatively were then asked to recall the year and month of occurrence. All interviews were conducted at home.

Most of the subjects reported having reached menarche (i.e., 826/839). A total of 13 subjects had reached menarche but could not remember the date of the event in either round. This left 813 cases who had reached menarche and who reported some data in at least one of the rounds. Comparison of the reported age at menarche for subjects giving both year and month in both rounds (n = 420) revealed much inconsistency in response, with the dates matching in only 176 subjects. When differences were between 1 and 24 mo values were averaged and included in the analyses (n - 237); cases with differences of >24 months were excluded (n = 7). If age at menarche was missing or the month was not recalled in one of the two rounds, the nonmissing value was selected or a value was assigned as described below (n = 393). When a month was not reported in either round but the reported year was the same, menarche was assumed to have occurred in midyear and an additional 6 mo of age was added to the reported year (n = 21). For cases where years differed by 1 or 2 but months were not given, the 1991 record for year was selected and an additional 6 mo was added to the reported year to estimate age at menarche (n = 90). The final sample consisted of 806 subjects who had reached menarche and 13 who had not.

Statistical analysi. Statistical analyses included Student's two-tailed t test of unequal sample size for comparison of mean ages at menarche in Atole and Fresco groups. Linear regression was used to evaluate the effects of possible covariates on age at menarche. The 13 cases that had not reached menarche, said to be "right censored," were left out of the above analyses (n = 806). Survival analysis techniques, primarily the SAS procedure PROC LIFEREG (SAS Institute, 1987), were used to include these cases (n = 819).

SES, village size and year of birth were included as predictors of age at menarche in the regression model. The SES score was derived from a principal components analysis and is based on household characteristics and an inventory of possessions in 1975; as such, the score measures accumulated wealth within the household (Rivera et al. 1995). The SES score was normalized within village with a mean of O and an SD of 1.

Differences in mean age at menarche were considered statistically significant at P<0.05. Main effects and interactions were considered significant at P<0.05 and P<0.10, respectively. All analyses were done using SASPC version 6.04.

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