Age at Menarche in a Rural Aymara-Speaking Community Located at High Altitude in Northern Chile

Abstract

Menarcheal information was collected in 1987 for rural Aymara speaking girls who reside at high altitude in the community of Putre (3,530 m), Parinacota Province, northern Chile. The study was based on the status quo investigation of 57 girls, aged 9 to 17 years, who attended a public school in Putre. Median age at menarche, which was estimated by probit analysis, was 13.7 years, about 0.3 year later than that reported in the literature for an urban Aymara sample from La Paz, Bolivia. In contrast to the limited data on median age at menarche in Aymara Indians, retrospective information is available for four comparative Aymara samples with medians ranging from 12.7 to 13.6 years. This considerable range is explained by differences in the nutritional level, by a possible secular effect, and by methodological, anthropological, as well as statistical sources of error in data collection and elaboration. Compared to samples of European ancestry living at high altitude, the Aymara are delayed in menarcheal age. This is probably attributable to the better nutritional status and socio-economic conditions of Europeans in South America. Key words: median age at menarche, high altitude, Amerindians, Aymara, Chile, Andes Introduction A trend toward earlier maturing was observed in Europeans and North Americans over the last hundred years (Eveleth and Tanner 1990). The most commonly used indicator for sexual development in girls has been the age of menarche. An increasingly earlier onset of menarcheal age of about 0.3 year per decade has been found as a general trend in industrialised countries (Eveleth and Tanner 1990). Studies have also shown that the onset of menarche is delayed among girls living at high-altitude in South America (Donayre 1966, Penaloza 1971). In the Peruvian highlands the age at which the secondary sexual characteristics in girls are attained is markedly delayed (Llerena 1973). Furthermore, measurements of luteinizing hormones in Peruvian girls indicate that those girls who live at high altitude attain the adult value one year later, that is by the age of twelve years, than girls living at sea level (Llerena 1973). Different environmental factors were considered to explain the observed differences in menarcheal age between highlanders and lowlanders. First, there is evidence that later age at menarche in highlanders is caused by poor nutrition in early life. It has been shown that well-nourished girls menstruate earlier than poorly-off ones (Colli 1986, 1988, Dreizen et aL 1967). Second, socio-economic differences were considered to affect age of menarche. Highland populations are generally of low socio-economic level (Leistol 1982). When living standards rise, age of menarche becomes lower. Third, the number of siblings was found to influence the onset of menarcheal age. It was noted that girls with large number of siblings have later menarche (Rona and Pereira 1974, Valsik 1965). Fourth, climatic factors, especially altitudinally mediated changes in the hormonal nature in women and men, are discussed as causative factors. Guerra Garcia (1971) for example demonstrated that the excretion of urinary testosterone in adults is significantly diminished at high altitude compared to that at sea level. The Aymara are a native highland population inhabiting the Central Andes region of South America for centuries. There are about two million Aymara speaking Indians (Hardman 1981), most of them living in western Bolivia and southern Peru. A small number of Aymara speakers resides in northern Chile being estimated according to different sources at 15,000-20,000 (Clair-Vasiliadis 1976) or 5,000 persons (Rothhammer and Schull 1980). The climatic conditions of their natural environment are characterised by low barometric pressure, diminished oxygen pressure, intense radiation, and marked diurnal temperature changes. The subsistence economy of the Aymara is based primarily upon agropastoralism. …