Exercise can help women going through any stage of breast cancer treatment to feel better both physically and emotionally, a new research review shows.

"It helps enhance mood and emotions during all phases of cancer treatment," lead investigator Dr. Susan R. Harris, an emeritus professor at the University of British Columbia in Vancouver, told Reuters Health. Recent studies showing that active breast cancer survivors reduce their risk of disease occurrence — and are less likely to die from the disease — make the case for exercise even more compelling, added Harris, herself a two-time breast cancer survivor.

She also noted that being active can help ward off weight gain, which is known to increase breast cancer mortality, especially for women who gain weight after undergoing treatment.

Harris and her team reviewed nine controlled trials, in which similar patients were randomly assigned to the exercise group or to a "control" group. The studies evaluated a wide range of physical activity, from aerobic exercise and resistance training to Tai Chi, dance and movement therapy, and gentle exercises done in a seated position.

Overall, the researchers say, the findings provide "strong evidence that exercise positively influences quality of life in women living with breast cancer." But it still isn't clear what type of exercise is best for a woman according to the stage of her treatment, they add.

Certain questions about safety also remain, Harris noted in an interview. For example, advanced breast cancer may spread to the bones and make them more fragile, so it's not clear that resistance exercise is safe for these patients. However, according to the researcher, aerobic exercise is "completely safe."

While some experts have raised concerns that exercise could worsen lymphedema, the swelling of the upper limb experienced by some breast cancer patients after surgery or radiation treatment, those fears have not been borne out, she added.

Breast cancer patients should understand that they don't need to exercise every single day to benefit from physical activity, Harris advised. There are times in the middle of treatment when a woman may simply feel too exhausted, she said, and on those days, it's perfectly OK to stay in bed.

Despite the clear benefits of exercise during breast cancer treatment, the researcher noted, doctors often don't give these patients recommendations on physical activity. "It's been kind of a black hole because oncologists don't know what to recommend, although they're getting better at it," Harris said.

Awareness is on the rise, she added; for example, the American College of Sports Medicine and the American Cancer Society now have a training program that certifies fitness professionals in working with cancer patients and survivors.