Secular trends in age at menarche among Caboclo populations from Pará, Amazonia, Brazil: 1930–1980

Abstract

The present study is part of a large research project on growth, development, nutrition, and health of Caboclo populations from the Brazilian Amazon. The aim of this paper is to analyze the age of menarche in adolescents (N ¼ 164) and adult women (219) in the studied populations. Caboclo are admixed rural, peasant groups that live along the Amazon river and its tributaries, and there are few previous studies about them. Probit analysis of the status quo data yielded a median age at menarche of 12.29 AE 1.76 years. The retrospective method was applied to recall data of the 77 post-menarcheal adolescents, yielding an average of 13.06 AE 1.27 years. Number of children in the family did not show any statistical influence on age at menarche in any age group. In adult women, age at menarche decreased from 14.50 in those born in 1930 to 12.88 for those born in 1980 (F ¼ 4.371, P ¼ 0.001). The downward trend found was, on average, 0.237 year per decade in the study period. The median age at menarche in the adolescents (12.29 years) is one of the lowest values found for Central and South American populations. In the ecological context, a low age at menarche could be an adaptive advantage because it provides a greater chance for reproduction at a young age in an environment where, until recently, life expectancy was low. As has been reported for other developing countries, the change found in age at menarche in the women born from the 1930s to the 1980s is likely to be related to changes in health and nutritional factors that occurred in Brazil because this country experienced significant improvement in living standards related to education, vaccination, and health conditions, which, although not equally, reached all regions after the 1960s.

Tendência secular da idade da menarca avaliada em relação ao índice de massa corporal

“…Estudando a probabilidade estimada da menarca de acordo com a idade, a mediana da menarca no NHANES III (The Third National Health and Nutrition Examination Survey) foi predita a partir dos dados do IMC de fato observado no NHANES III. Os autores, então, compararam a idade predita (12, (22).…”

Parental age at childbirth and age of menarche in the offspring

“…Since AOM has notably declined over time worldwide (Helm and Helm, 1984;Adadevoh et al, 1989;Papadimitriou et al 1999;Olesen et al, 2000;Anderson et al, 2003;Do Lago et al, 2003;Silva and Padez, 2006)-much more than genetic factors alone can explain-this decrease must presumably have, at least in part, environmental causes. For example, in Denmark, the average AOM declined by 4 months from 13.40 to 13.03 years between 1965/ 1966 and 1982/1983, a 2.4 months drop in AOM per decade was reported in Brazil among a cohort of women born between 1931 and 1977, and in the USA an average drop in AOM by 2.5 months was observed between 1963-1970 and 1988-1994 with a further decline by 2.3 months in (Helm and Helm, 1984Anderson et al, 2003;Do Lago et al, 2003;Anderson and Must, 2005).…”

Age of Onset, Nutritional Determinants, and Seasonal Variations in Menarche in Rural Bangladesh

“…We believe that the study of onset of menarche is important not only from an anthropological point of view but also because the mean menarcheal age has been accepted as a "particularly sensitive indicator of the biosocial status of the population" (12). The mean age at menarche in rural Bangladesh was last estimated more than a decade ago, and a number of biological, social and ecological factors have likely changed since then.…”