Genetics appear to play a key role in the timing of a girl’s first period, the BBC reports. Researchers have discovered two genes that influence the onset of puberty in both sexes, adjacent to genes controlling height and weight. The findings are important because early menstruation can contribute to a number of health problems for women, including heart disease, osteoporosis, and breast cancer.
“Early menstruation is a health issue because beyond being an inconvenient surprise for a girl and her parents, it’s also associated with a higher risk of a variety of diseases and psychological problems,” said one of the researchers. Rising obesity rates are often blamed for the spike in early-bloomers, as heavier girls tend to get their periods sooner.