Women who exercise regularly in their teens and young adulthood lower their risk of developing breast cancer before menopause compared with those who are more sedentary, a new U.S. study has found.
The study, published yesterday in the Journal of the National Cancer Institute, examined 65,000 women and found that the most physically active were 23 percent less likely to develop premenopausal breast cancer than those who exercised the least. High levels of exercise between ages 12 and 22 reaped the most protective benefit, researchers found.
“We don’t have a lot of prevention strategies for premenopausal breast cancer, but our findings clearly show that physical activity during adolescence and young adulthood can pay off in the long run by reducing a woman’s risk of early breast cancer,” said lead researcher Graham Colditz, professor and associate director of prevention and control at the Alvin J. Siteman Cancer Center at Washington University School of Medicine and Barnes-Jewish Hospital.
Many studies have shown that physical activity reduces breast cancer risk in postmenopausal women; but until now, there was only limited and inconsistent studies documenting a link in premenopausal women, Dr. Colditz said.
“We wanted to get to the bottom of it,” he added.
His team of researchers from UW School of Medicine and Harvard University studied 65,000 registered nurses aged 24 to 42, collecting detailed information about how much leisure time physical activity they had done since age 12. After six years of follow-up, 550 of the women had been diagnosed with breast cancer.
Their analysis showed that “being active in youth seems to have a benefit that carries over,” Dr. Colditz said.
He added, “You don’t have to be a marathon runner to get the risk-reducing benefits.”
The most physically active women reported levels of exercise equivalent to about 3.25 hours per week of running or 13 hours per week of walking. Reduced risk was linked to total activity level and wasn’t associated with one particular sport or activity.
Dr. Colditz and the team said more research is needed to find out whether exercise lowers breast cancer risk. One theory, he said, is that exercise reduces the woman’s exposure to estrogen, a hormone linked to breast cancer. Other theories involve insulin, he said.
Beyond this, he said, societal leaders must focus on coming up with ways to encourage young girls to exercise.
“Part of the question has to be: ’What can we do in society?’ ” he said.
The American Cancer Society (ACS) and National Cancer Institute provided the grant funding for the study.
The ACS estimates there will be about 182,460 new cases of invasive breast cancer diagnosed this year and about 40,930 breast cancer deaths (40,480 women, 450 men). Breast cancer ranks second in cancer deaths in women, after lung cancer. Death rates from breast cancer have decreased steadily in women, however, since 1990, largely because of earlier detection and better treatments, according to ACS.
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