NEW YORK (Reuters Health) - Moderate-intensity exercise, such as a brisk 20-minute walk three or more times a week, maintains or even increases erythrocyte levels during radiation therapy for breast cancer, researchers report in the November 15th issue of Cancer.

Investigators in Michigan and Ontario studied 20 sedentary females between the ages of 35 and 655 who were receiving a 7-week course of radiation therapy for breast carcinoma.

The women were randomized to stretching activities 3-5 days a week or to an aerobic exercise program, consisting of 20-45 minutes of walking three-to-five times a week, at a pace targeted to achieve a heart rate that was 50% to 70% of maximum. The exercise program was maintained throughout the course of radiation.

Peak aerobic capacity increased 6.3% with aerobic exercise and decreased 4.6% with stretching. Red blood cell counts increased from 4.10 to 4.21 million cells/microliter with aerobic exercise and decreased from 4.30 to 4.19 million cells/microliter with stretching. Differences between the groups in RBC changes were significant.

Hematocrit levels increased from 38.0% at baseline to 38.8% with aerobic exercise. It dropped from a baseline level of 37.4% to 36.5% after seven weeks in the stretching program. Hemoglobin increased from 12.3 g/dL to 12.4% g/dL with exercise and dropped from 12.25 g/dL to 11.77 g/dL with stretching.

"Within this small study, the ladies who did not exercise experienced statistically significant declines in hemoglobin, red blood cell counts, and hematocrit levels," principal investigator Dr. Jacqueline S. Drouin, at the University of Michigan in Flint, told Reuters Health. "Those women in the exercise group experienced small increases in all of these values but the changes were not statistically significant, most likely because of the small sample size."

"Further study is required to see what the impact is on other health conditions, local and regional failure rates, and survival rates in this population," she commented.

Also, she added, "Further study is required to determine whether the results of this study occur in other types of cancer being treated by radiation as well as in people receiving chemotherapy."

"Again this was a very small study of 20 subjects," Dr. Drouin emphasized. "However, the design was a randomized controlled clinical trial and none of the ladies had exercised for three months prior to the study. The study found that moderate intensity aerobic exercise of walking was a safe and economical method to preserve erythrocyte levels during radiation treatment for breast cancer."

Cancer 2006;107:2490-2495.