Early exercise makes a difference

New research reinforces the benefits of exercise, in this case with a finding that exercise during the teen years can help protect girls from adult breast cancer:

Women who were physically active as teens and young adults were 23 percent less likely to develop premenopausal breast cancer than women who grew up sedentary, researchers report Wednesday in the Journal of the National Cancer Institute.

The biggest impact was regular exercise from ages 12 to 22.

"This is not the extreme athlete," Colditz cautioned.

The women at lowest risk reported doing 3 hours and 15 minutes of running or other vigorous activity a week or, for the less athletic, 13 hours a week of walking. Typically, the teens reported more strenuous exercise while during adulthood, walking was most common.

Why would it help? A big point of exercise in middle age and beyond is to keep off the pounds. After menopause, fat tissue is a chief source of estrogen.

In youth, however, the theory is that physical activity itself lowers estrogen levels. Studies of teen athletes show that very intense exercise can delay onset of menstrual cycles and cause irregular periods.

The moderate exercise reported in this study was nowhere near enough for those big changes. But it probably was enough to cause slight yet still helpful hormone changes, said Dr. Alpa Patel, a cancer prevention specialist at the American Cancer Society, who praised the new research.

I've got one teenage niece and one who'll be there soon... and, incidentally, it's their mother's birthday. Happy Birthday, Molly!