As if we need more reasons to can the soda habit in our households, yet another has surfaced — especially for families with young girls. New research suggests that sugary beverages may be one reason girls are getting their first periods at increasingly younger ages. The average has dropped from 16 or 17 years old a century ago to under 13 now.

Karin Michels, ScD, PhD, an associate professor of epidemiology at Harvard Medical School, followed more than 5,500 girls ages 9 to 14 for five years. She found that those who downed one and a half servings of a sugary beverage a day started menstruating nearly three months earlier than those who drank two or fewer servings per week. One and half servings of a sweet drink is basically a can of soda. Besides regular soft drinks, the study considered any beverages with added sugar to be a problem (so unsweetened fruit juice and diet soda didn’t count as problematic).

At first Michels thought obesity might be the link between sugary drinks and early periods. Consumption of soda and other sugar-laden beverages is a major factor in obesity among kids. And studies show that girls who start menstruating at a young age tend to be overweight. But in Michels’ study, the soda drinkers got their periods early regardless of their body mass index. She suspects that the association between sugary beverages and early menstruation has to do with blood sugar levels.

"If you eat a lot of table sugar you get insulin spikes,” she explains. “Increases in insulin levels are associated with high levels of estrogen and growth hormones, which can lead to earlier menstruation."

What’s bad about early periods?

"The longer a girl’s reproductive life span, the longer she’s exposed to reproductive hormones,” Michels explains. “This puts her at greater risk of breast cancer.” Each one-year decrease in the age of first period is linked with a 5 percent increase in breast cancer risk. So while a three-month earlier start is likely to have only a modest effect on breast cancer risk, Michels notes that many girls are drinking more than a can of soda, or the equivalent in other sweetened beverages, a day.

Getting her period at a young age can set a girl up for other problems as well. Research has found links between early menstruation and endometrial cancer, adult-onset asthma and type 2 diabetes.

Besides the bubbles

Soda is only one in a growing list of reasons for early periods. Here are other potential factors that may be pushing young girls into puberty:

Household chemicals. Researchers at the Centers for Disease Control and Prevention found that girls exposed to dichlorobenzene, a solvent used in some mothballs, toilet bowl deodorizers and air fresheners, may get their periods earlier. Dichlorobenzene mimics estrogen, which has an impact on menstruation.

Vitamin D deficiency. Girls with low levels of vitamin D were twice as likely to start their periods early than were those who had healthy levels of the nutrient, according to a study published in the American Journal of Clinical Nutrition.

Stress, social hardships, family stress. Problems at home, with friends and other sources of stress have been found to bring on the start of menstruation earlier, other research has found.

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.