(NaturalNews) Women who exercise regularly during their younger years are 23 percent less likely to develop breast cancer as adults, according to a new study conducted by researchers from the Washington University School of Medicine in St. Louis and published in the Journal of the National Cancer Institute.
Researchers questioned 65,000 female nurses between the ages of 24 and 42 about their exercise histories back to the age of 12, then followed them for six years. Women who had engaged in at least three hours and 15 minutes of vigorous activity, such as running, each week between the ages of 12 and 22 were 23 percent less likely to develop cancer during the study period than women who had not exercised that much. The same protective benefit seemed to accrue to women who engaged in 13 hours per week of moderate exercise - such as walking - instead.
Roughly a quarter of breast cancer cases occur in the age group examined in the current study. These earlier developing cases of breast cancer are generally more aggressive and dangerous.
The researchers were not clear on the mechanism by which exercise early in life helps prevent breast cancer later in life. It is known that exercise can decrease the levels of female sex hormones, such that there is a well-documented tendency of young runners and other athletes to have a delayed onset of menstruation. While the levels of exercise reported in the current study were nowhere near that level, some researchers believe that they may still cause slight changes in hormone levels, enough to affect cancer risk.
"This really points to the benefit of sustained physical activity from adolescence through the adult years, to get the maximum benefit," lead author Graham Colditz said.
Prior studies have demonstrated that exercise in middle age also decreases the risk of breast cancer.