Scientists have previously observed that girls are having their first periods earlier than they once did, and a new study offers a possible reason: sugary beverages like soda. Researchers studied 5,583 US children between 1996 and 2001; they found that girls ages nine to 14 who downed an average of more than 1.5 sugary drinks each day experienced their first periods 2.7 months earlier than girls who had no more than two each week, the Press Association reports via the Guardian. That's of some concern, experts say, because earlier periods have been linked to a higher risk of breast cancer. Obesity has also been associated with earlier periods, but the study's findings held true "independently of body mass index," says a researcher; the results were also independent of physical activity and overall food intake, Today reports.
One possible explanation is that added-sugar beverages can drive up insulin, which can increase sex hormone concentrations, which in turn can lead to earlier periods. (Diet sodas and fruit juices weren't linked to earlier periods, Medical Daily reports.) Today points to one issue with the study: It didn't define the serving size involved. And an outside expert wonders whether 2.7 months really means much—but the lead author says it does. The results "are actually very powerful because consumption of these kinds of drinks is something that can be modified," she notes. (And it's probably a good idea to stay off the soda anyway: Another study finds it can age our cells as much as smoking can.)