Women with breast cancer tend to exercise less after being diagnosed with the disease, a new study has found, even though physical activity is an important part of recovery.

By getting less physical activity, the researchers said, women are putting themselves at risk for weight gain, which may increase the risk of cancer recurrence.

Lead researcher Melinda Irwin, PhD, of Yale University, and colleagues from five other institutions studied 812 women recently diagnosed with breast cancer. They asked the women about the type of exercise they got in the year before diagnosis and in the year after diagnosis. The questions addressed 29 activities, including walking, jogging, aerobics and sports, as well as house cleaning and yard work.

The researchers found that on average, women got two fewer hours of physical activity per week after being diagnosed with breast cancer than before – a reduction of 11%.

Although some decrease was expected because of the fatigue, nausea, and pain often associated with breast cancer treatment, Irwin said she was surprised by the extent.

Women cut back on light activity like housework, as well as on more vigorous activities, such as sports. And even patients who only had surgery, or who had surgery and radiation but no chemotherapy, exercised less. Patients who were treated with surgery, radiation, and chemotherapy showed the greatest declines in physical activity.

Overweight and obese women showed greater decreases in physical activity after diagnosis when compared to lean women. The finding is troubling, Irwin said, because heavier women are already at greater risk of recurrence and poor prognosis.

The study results point to a gap in the treatment of cancer patients, Irwin said.

“When a woman is diagnosed with any cancer… part of the treatment process needs to be rehabilitation related to activity level, diet, weight control,” Irwin said.

Previous studies have shown that exercise can help lessen the fatigue associated with cancer treatment, and help patients improve their physical functioning.

Being diagnosed with cancer can provide an opportunity to adopt healthier behaviors, Irwin noted. “If they’re currently meeting the recommendations (for exercise and body weight), they need to maintain that. If they weren’t doing any exercise, we need to give them a program that works for them.”

Irwin said her study provides evidence that some of the weight gain associated with breast cancer treatment could be related to decreases in physical activity, in addition to the effects of diet changes and drug side effects. The same group of patients participating in this study is still being followed to determine what effect the reduced exercise level may have on weight, hormone levels, and other factors.

More research also is needed to determine whether increasing physical activity levels will actually improve the prognosis of breast cancer patients, the report concluded.