Scientists looking at patterns of growth and maturity in the United States have noted that many girls are starting puberty earlier than they were 30 years ago. At the same time, rates of obesity for American children have been rising. Some medical researchers have theorized that increased weight in girls might be contributing to earlier puberty. Puberty in girls is marked by the formation of physical characteristics such as breast buds, growth of bodily hair and menarche - the beginning of menstruation.
Dr. Joyce Lee, a professor of pediatrics at the University of Michigan, examined data from an on-going government study that's following girls from the time they were toddlers until they become teenagers. She and her colleagues looked at the body mass index - or BMI - of more than 350 girls from the time they were 3 years old. Body mass index is a standard measure of body fat calculated using both weight and height.
"We found that girls with higher body mass index at 36 months of age were more likely to have earlier onset of puberty, which was defined as breast bud development by nine years of age," she explains. "We also found that girls who had a greater increase in their BMI between 36 months and seven years of age were more likely to experience earlier puberty."
Lee says it was important to track the weight of the girls from well before the onset of puberty in order to get some answers about the relationship between the two. She compares it to the unanswerable question: Which came first, the chicken or the egg? "We know that girls who have early onset of puberty tend to be heavier or tend to have higher BMIs. But puberty is also a time when girls (normally) gain a lot of weight. So it wasn't clear if the weight gain was causing the puberty or if the puberty was causing the weight gain." Lee says the study lends credence to the idea that carrying extra weight from the time they're very young contributes to girls starting puberty earlier.
The researcher says it's still not clear if preventing weight gain could delay the onset of puberty. But she points out that delaying the onset of puberty could be beneficial, since there are long-term psychosocial and health effects of its early arrival. "We know from studies that earlier onset of puberty can be associated with increased rates of behavioral problems and psychosocial difficulties, earlier initiation of alcohol use and sexual intercourse and increased rates of adult obesity and breast cancer."
Lee notes that it's also beneficial to prevent early weight gain, since obesity can lead to diabetes, high blood pressure and high cholesterol in early adulthood. Her research appears in the journal Pediatrics.