Date Published: April 18, 2019
Publisher: Public Library of Science
Author(s): Gabriel Šaffa, Anna Maria Kubicka, Martin Hromada, Karen Leslie Kramer, Kannan Navaneetham.
Timing of menarche has largely been studied in the context of a secular trend. However, since mortality and fertility rates are fundamental demographic factors linked to a population’s developmental and reproductive characteristics, we expect that the timing of menarche, a precondition to reproduction, is also associated with these vital rates. We conduct an analysis of 89 countries and 21 demographic, socioeconomic, nutritional, and educational variables selected for their known influence on menarche. Model results predict that a country’s fertility and adult female mortality rates are significant predictors of mean age at menarche, while other covariates are not. Specifically, menarche is delayed in countries with high mortality and high fertility, which may be proxies for assessing overall environmental quality. We emphasize that, for a comprehensive understanding of the timing of menarche, it is critical to take into account both individual- and population-level influences.
Menarche is a key life history event shaping the onset of a female’s reproductive career [1–8]. Unlike other pubertal characteristics that manifest gradually (e.g. breast and pubic hair development, fat deposition, and the adolescent growth spurt), menarche is a discreet event [6,9]. As such, it is a useful, but underrepresented, variable in demographic research .
The results reveal two major findings. First, of the 21 covariates, fertility rate (children per woman) and adult female mortality rate (the probability of female dying between the ages 15–60) are the best predictors of variation in the timing of menarche across countries in our sample (Table 3). Although improvements in socioeconomic, health, and nutritional conditions are factors responsible for a shift to an earlier age at menarche at the individual level, our model results show that at the population level, the timing of menarche is strongly associated with fertility and mortality rates. Second, fertility (N = 89, SC = 0.681, p<0.001) and adult female mortality rates (N = 89, SC = 0.685, p<0.001) correlate positively with menarche (S5 Table), indicating that both high fertility and high mortality are associated with later menarche. As we argue below, our results are not mutually exclusive with previous findings but offer a perspective on how factors at the individual level can be translated into and viewed from the population level and vice versa. We discuss our findings in light of life history theory. This study investigated population-level influences on the timing of menarche. We found that (adult female) mortality and fertility rates have significant effect on the variation in mean menarcheal age across countries in our sample, which is consistent with general life history framework. It is clear that the energetic and social resources available to an individual have a direct influence on the timing of menarche. At the population level, if this is reflected in mortality and fertility rates, the latter may act as proxies for assessing overall quality of the environment. This, in turn, can exert their indirect effects on the individual timing of menarche (Fig 2). Thus, for a comprehensive understanding of the timing of menarche it is critical to take into account both individual- and population-level influences. We assert that a population-level age at menarche can be another important demographic variable. Source: http://doi.org/10.1371/journal.pone.0215462