Vigorous Exercise Cuts Breast Cancer Risk

Exercise cuts a woman's risk of breast cancer after menopause -- but only vigorous exercise, a National Cancer Institute study shows.

Moderate exercise did not cut breast cancer risk. Vigorous exercise did, but only in women who were not overweight. However, it's possible that overweight and obese women found moderate exercise more taxing and misreported it as strenuous exercise.

The findings suggest that exercise itself protects against breast cancer, regardless of whether it leads to weight loss, note Michael F. Leitzmann, MD, and colleagues at the National Cancer Institute.

The researchers analyzed data on more than 32,000 postmenopausal women collected over 11 years as part of the Breast Cancer Detection Demonstration Project.

Women were asked about their exercise habits, and Leitzmann's team rated their exercise as "moderate" or "vigorous."

Activities rated as "moderate" were rated "non-vigorous." They included:

Light housework
Vacuuming
Washing clothes
Painting
Home repairs
Lawn mowing
General gardening
Raking
Light sports or exercise
Walking
Hiking
Light jogging
Recreational tennis
Bowling
Golf
Bicycling on level ground
"We observed no association between non-vigorous activity and breast cancer," Leitzmann and colleagues report.

Activities rated as "vigorous" include:

Housework such as scrubbing floors or washing windows
Heavy yard work
Digging in the garden
Chopping wood
Strenuous sports or exercise
Running
Fast jogging
Competitive tennis
Aerobics
Bicycling on hills
Fast dancing
Overall, women who got a lot of vigorous exercise had only a small decrease in breast cancer. But the researchers saw a much stronger effect in women who were neither overweight nor obese.

"When we evaluated the relation of vigorous activity to breast cancer among women who were of normal weight ... the risk among women reporting the highest amount of vigorous activity decreased by about 30% compared with women with no vigorous activity," Leitzmann and colleagues found.

The study appears in the Oct. 31 online issue of the open-access journal Breast Cancer Research. Leitzmann is now with University Hospital Regensburg, Germany.