Total Estradiol Levels in Migrant and British-Born British Pakistani Women: Investigating Early Life Influences on Ovarian Function
ABSTRACT The purpose of this study was to test the hypothesis that women who grow up in energetically stressed environments have later menarche and lower total estradiol levels during their reproductive years than do women who grow up in less energetically stressed environments. We assessed total estradiol in a serum sample taken 9-11 days after the start of the menstrual cycle in 26 women who grew up in Pakistan and migrated to the UK as adults, in 28 British-born British Pakistani women, and in 25 British-born women of European origin. Women who grew up in Pakistan reported a later menarche than women who grew up in the UK. However, we found no significant differences between the groups in total estradiol level. Thus our findings do not support the hypothesis that estradiol levels are partially determined during early life. However, having considered our findings in relation to those of other studies, we conclude that new methodological approaches are needed to provide a more definitive test of the hypothesis.
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ABSTRACT: Human reproductive ecology (HRE) is the study of the mechanisms that link variation in reproductive traits with variation in local habitats. Empirical and theoretical contributions from biological anthropology, physiology, and demography have established the foundation necessary for developing a comprehensive understanding, grounded in life history theory (LHT), of temporal, individual, and populational variation in women's reproductive functioning. LHT posits that natural selection leads to the evolution of mechanisms that tend to allocate resources to the competing demands of growth, reproduction, and survival such that fitness is locally maximized. (That is, among alternative allocation patterns exhibited in a population, those having the highest inclusive fitness will become more common over generational time.) Hence, strategic modulation of reproductive effort is potentially adaptive because investment in a new conception may risk one's own survival, future reproductive opportunities, and/or current offspring survival. The hypothalamic-pituitary-ovarian (HPO) axis is the principal neuroendocrine pathway by which the human female modulates reproductive functioning according to the changing conditions in her habitat. Adjustments of reproductive investment in a potential conception are manifested in temporal and individual variation in ovarian cycle length, ovulation, hormone levels, and the probability of conception. Understanding the extent and causes of adaptive and non-adaptive variation in ovarian functioning is fundamental to ascertaining the proximate and remote determinants of human reproductive patterns. In this review I consider what is known and what still needs to be learned of the ecology of women's reproductive biology, beginning with a discussion of the principal explanatory frameworks in HRE and the biometry of ovarian functioning. Turning next to empirical studies, it is evident that marked variation between cycles, women, and populations is the norm rather than an aberration. Other than woman's age, the determinants of these differences are not well characterized, although developmental conditions, dietary practices, genetic variation, and epigenetic mechanisms have all been hypothesized to play some role. It is also evident that the reproductive functioning of women born and living in arduous conditions is not analogous to that of athletes, dieters, or even the lower end of the "normal range" of HPO functioning in wealthier populations. Contrary to the presumption that humans have low fecundity and an inefficient reproductive system, both theory and present evidence suggest that we may actually have very high fecundity and a reproductive system that has evolved to be flexible, ruthlessly efficient and, most importantly, strategic.American Journal of Physical Anthropology 01/2009; 140 Suppl 49:95-136. DOI:10.1002/ajpa.21195 · 2.51 Impact Factor
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ABSTRACT: Early puberty often occurs in migrants from less to more economically developed locations, particularly among girls, perhaps because of mismatched inter-generational conditions. However, migrants may differ from their host population in many ways. In an ethnically homogenous Chinese population in a developed environment, we examined the association of mother's growth environment (proxied by migration status) with age at onset of puberty. We assessed differences by sex and whether associations were independent of intra-uterine growth. We used interval-censored survival analyses in 3832 boys and 3279 girls (follow-up rate of 92%) from the 'Children of 1997' birth cohort, comprising 88% of births in Hong Kong in April and May 1997, to examine the adjusted association of mother's migration status (born and raised in mainland China or in comparatively more developed Hong Kong), with clinically assessed age at onset of puberty (Tanner stage II for breast/genital and pubic hair development). Children with mothers from a less developed environment had earlier onset of breast/genital [time ratio (TR) 0.987, 95% confidence intervals (CIs) 0.980-0.993] and pubic hair (TR 0.993, 95% CI 0.986-1.000) development, independent of birth size for gestational age and socio-economic position, possibly with a more marked association in girls. Mismatch of growth conditions between mothers and children was associated with younger age at onset of puberty. Given the association of early puberty with chronic diseases, inter-generational influences may be relevant to the emerging epidemics of these diseases in rapidly developing populations where age of puberty is declining sharply.International Journal of Epidemiology 12/2011; 41(1):292-300. DOI:10.1093/ije/dyr163 · 9.20 Impact Factor