Writing in Women’s eNews, Molly M. Ginty looks more closely at the Pediatrics study and at another March study, published in the Journal of Adolescent Health, that found girls’ girth is also likely responsible for earlier onsets of menstruation: The average age of first menstruation, writes Ginty, declined from 13.3 years in girls born before 1920 to 12.4 years in those born during the early 1980s.
Though research linking weight to puberty dates back for centuries, the recent Pediatrics paper was the first to peg which comes first. It indicated weight gain triggers early puberty, instead of early puberty triggering weight gain.
In the United States in the early 1800s, breast buds and menarche arrived around ages 13 and 16 respectively. Those changes now come around ages 9 and a half and 12 and a half.
Scientists say girls are eating more food and putting on pounds, which is causing their bodies to boost production of the hormone leptin.
“Leptin is made in fat cells and is necessary for normal reproductive function,” says Paul Kaplowitz, chief of endocrinology at the Children’s National Medical Center in Washington and author of “Early Puberty in Girls,” published in 2004 by Random House. “There’s an evolutionary benefit to this. You don’t want to get pregnant if there isn’t enough food for you to carry a pregnancy successfully. You would risk the baby’s life and your own.”
Ginty also covers other factors that can accelerate puberty, including exposure to chemicals, birth weight, genetics and home environment — researchers have found that absence of a father and the presence of an unrelated male, such as stepfather speeds up the process.
A large-scale study is in the works:
To better track the physical causes of puberty, the Bethesda, Md.-based National Institutes of Health has launched a study of 14,000 children born in 2001 that is “longitudinal” and will follow its subjects over time. The results of this research will not be available for 10 years or more.