Scientists studying factors affecting the pace of sexual development have identified a variety of factors that can alter the timing of puberty. While solid data exist demonstrating links between people and several of these causes, those data address what has happened to small groups of people (or individuals). As yet we lack strong evidence linking any of them to widespread changes in the timing of puberty.

Obesity
Many studies have revealed links between nutritional status, weight and the timing of sexual development, from work documenting early puberty in obese women (Zacharias et al. 1970) to delayed puberty in thin ballet dancers (Frisch and McArthur 1974). The single best predictor for the onset of menarche is weight, which is approximately 106 pounds when menarche begins (Moffitt et al. 1992).

While the causal mechanisms are far from complete resolution, it appears that a recently discovered hormone, leptin, is involved. Puberty can be advanced experimentally in mice by increasing leptin levels (Chehab et al. 1997). Leptin links puberty to obesity because leptin is secreted in fatty (adipose) tissue... more adipose tissue leads to more leptin, which (according to these mouse studies) then triggers earlier puberty. Measurements of obese people indicate they have more leptin circulating in their blood.

[One of the complications of this hypothesis is determining what is causing the changes in obesity patterns which in turn (by this hypothesis) are driving the changes in puberty. Many causes have been cited, including life style changes --more fast food, less walking, etc. There are biological reasons, including data from animals, that suggest contamination may also be involved by interfering with leptin's role in weight regulation.]

Social factors
Much research has focused on the impact on sexual development of the family environment in which a girl is growing up. Some studies examine the relationship between mother and daughter in affecting the timing of the daughter's sexual maturation. Others have looked at the impact of the father. One finding is that girls growing up in stressed families reach puberty earlier (Moffitt et al. 1992).

Studies of girls growing up in families indicate that if the father is absent or if an adult male who is not the girl's father is present, puberty will occur earlier (Ellis and Garber 2000).

Common wisdom--but no data--suggest that the increasingly overt sexuality of popular media may stimulate earlier sexual development.

Contamination
A wealth of data from experiments with animals show that the rate of sexual development is vulnerable to various contaminants, contaminants to which people are widely exposed. Some epidemiological studies and case histories in the medical literature indicate sexual development in people also can be affected by contamination.

Data are also available linking human exposure to contaminants to earlier puberty. Some of these studies come from epidemiological work with exposed populations. Others are from case histories in medicine.

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