Exercise may help to prevent breast cancer and help women who have it to feel better, two studies suggest.

Researchers in the U.S. interviewed 1,630 women without breast cancer, 1,689 survivors of non-invasive breast cancer and 6,391 survivors of invasive breast cancer about their physical activity, occupation, family history of breast cancer, menopausal status, and body mass index. The women were all between the ages of 20 and 69.

'The take-home message for women should be that it is never too late to begin exercising.'—Study author Brian Sprague

Women who said they did six or more hours per week of strenuous exercise may have reduced their risk of invasive breast cancer by 23 per cent compared to sedentary women, according to the study in the February issue of Cancer Epidemiology Biomarkers & Prevention.

"A woman's hormone levels naturally fluctuate throughout her life, and we have found that exercise likely offers protection against breast cancer regardless of a woman's stage in life," said the study's lead author, Brian Sprague, of the University of Wisconsin. "The take-home message for women should be that it is never too late to begin exercising."

High levels of estrogen have been linked to a higher risk of developing breast cancer. Women who exercise heavily tend to be older at the time of their first period and produce estrogen for a shorter time, lowering their exposure to the hormone over their lifetime, the researchers said.

It is also possible that exercise helps by preventing weight gain, regulating insulin sensitivity and changing immune function, the team said.

The benefits were only seen in women without a family history of breast cancer. Other risk factors for breast cancer were taken into account. 

The team called for more research into forms of physical activity, such as household chores in addition to recreational and occupational activity.

Exercise for women with breast cancer

A second study in Friday's online issue of the British Medical Journal looked at the benefits of exercise for women with early breast cancer.

Nanette Mutrie, a professor of exercise and sport psychology at the University of Strathclyde in Glasgow, Scotland, and her team studied 203 women with early-stage breast cancer who were 51 years old on average and were sedentary.

The women all had a lumpectomy or mastectomy and were getting chemotherapy or radiation therapy to prevent a recurrence of cancer. The participants completed surveys about their mood and quality of life, did a walking test and had their shoulder mobility assessed.

Half of the women then took a 12-week group exercise class and the rest did not. Those in the exercise were offered two 45-minute classes with an exercise specialist each week and similar exercises to do at home once a week.

After the 12 weeks, those in the exercise group showed better physical functional ability, such as walking greater distances or moving their shoulders, and psychological well-being, based on their outlook.

After six months, most of the beneficial effects in the exercise group were maintained, the team found.

"Clinicians should encourage activity for their patients. Policy makers should consider the inclusion of exercise opportunities in cancer rehabilitation services," the study's authors concluded.