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Originally Posted by SynthethicalY
ThePits I have heard it is due to the hormones added to milk that girls are getting their menstruation cycle much faster now.
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I'm not quite sure about this hormone thing, as I'm sure the story isn't much different in Canada where the use of growth hormones in dairy production is illegal. Rather it might be related to the increase in dietary fat, as sex hormones (such as estrogen and progesterone) are derivatives of cholesterol. Anorexia can mess up the mentrual cycle for this reason, as the body's fat reserves dry up. Also, the prevalence of childhood obesity can perhaps be linked to earlier fertility (higher fat proportion, etc). Then again, what I'm saying here comes from a couple of classes and some logical thinking, and my memory needs some refreshing (helloooo Pubmed!).
By the way pregnancy intervals were much longer before agriculture for this reason too, as the nomadic lifestyle of hunters-gatherers had a large impact on the body's fat reserves.
Edit: two abstracts from PubMed
From
J Obstet Gynecol Neonatal Nurs. 2007 May-Jun;36(3):263-74
Cesario and Hughes: Precocious puberty: a comprehensive review of literature
Eighty-two studies or case reports met the criteria for inclusion in this literature review that captured six attributable causes of early sexual maturation in female children. These included genetic, ethnic, and pediatric obesity, as well as environmental toxins that disrupt endocrine function (chemicals, toxins, plasticizers, infant feeding methods, skin and hair products, assisted reproductive technologies), psychosocial stress, and early exposure to a sexualized society. The robustness of the reports varied and few of the studies were widely generalizable but did offer suggestions for assessment and nursing care. CONCLUSIONS: Precocious puberty has health and social implications that are complex and influenced by multiple factors. Further research is needed to expand and elucidate theoretical relationships between the early development of secondary sex characteristics in young girls and the proposed causative factors.
From
Mol Cell Endocrinol. 2006 Jul 25;254-255:8-12. Epub 2006 Jun 6
Ong et al - Lessons from large population studies on timing and tempo of puberty (secular trends and relation to body size): the European trend.
Ever since the publication of the first textbook on human growth by Johann Augustin Stoeller in 1729, temporal changes (or secular trends) in growth and pubertal maturation have been observed throughout the world. Data covering the longest time span are often reported from European populations. For example, in Norway and Denmark the age at menarche has fallen rapidly since the 19th century, by up to 12 months per decade. These changes have broadly paralleled increases in adult height in most European countries over the last century, with rates of around 10-30mm per decade. These secular trends are influenced by background ethnic, geographical and socio-economic factors, and clearly nutritional changes have an important role as reflected by positive correlations between age at puberty onset or age at menarche and childhood body size. Changes in height, pubertal maturation, and childhood body size have all also been related to rate of weight gain in infancy, and there is growing evidence to suggest that this early postnatal period may represent an early window of susceptibility to long-term 'programming' of various outcomes in humans. There is debate as to whether the secular trends in pubertal maturation are continuing or have reached their limit. Even where temporal changes are overall clearly significant, they are most marked in the more nutritionally deprived sub-groups. Whether over-nutrition and increasing childhood obesity will continue to lead earlier puberty is uncertain. The confirmation of an estimated advance in the age at menarche of 6-12 months per 100 years will require a long-term perspective on behalf of current investigators, and new consideration of methodological approaches in an age of increasing recognition of children's rights for privacy.