In the blame game of early onset puberty in girls, many fingers have pointed to "hormones in milk" as the culprit. This claim really got going when recombinant bovine somatotropin was approved for commercial use in 1994.
Two or three weeks ago, a host of a Kansas City talk radio show was among the latest to spread this idea.
Now, a review published in the Frontiers in Endocrinology points to other potential causes. Read more.
One guilty party? Childhood obesity.
Childhood obesity has already been connected to numerous healthy issues in youth, including glucose intolerance, hypertension and high cholesterol. These metabolic conditions could impact the reproductive system, as well.
"The issue of so many humans being obese is very recent in evolutionary terms, and since nutritional status is important to reproduction, metabolic syndromes caused by obesity may profoundly affect reproductive capacity," Patrick Chappell, an assistant professor of veterinary medicine at Oregon State University and an author of the recent report, says in a news release.
Theories explaining the relationship between obesity and early puberty include the secretion of a key hormone called kisspeptin. Researchers believe that the secretion of kisspeptin may be disrupted in children who have excess fat, thereby impacting the timing of puberty.
More research into the link between childhood obesity and early puberty in girls is likely.
The review also explored other potential causes of altered puberty, including the disruption of circadian clocks, which are the body"s natural rhythms of night and day. The secretion of hormones such as cortisol, testosterone and insulin has been shown to be affected by disrupted sleep-wake cycles. Early childhood exposure to hormones may also play a role in early puberty, but more studies are needed.
This isn"t the first study to find other causes for early onset of puberty, rather than blaming "hormones in milk". In 2005, The New York Times debunked the claim, also pointing to obesity as the key player in early puberty in girls.
A 2001 study, led by Paul Kaplowitz, the author of "Early Puberty in Girls," found that girls with higher body-mass indexes were more likely to experience accelerated puberty timing.
Many studies have connected milk consumption with a lower body mass index, further debunking the claim that milk is responsible for reproductive issues in girls.