Regular exercise before breast cancer onset may protect against death due to cardiac cause

The five-year survival rate for breast cancer has increased due to availability of better drugs and earlier diagnosis. Unfortunately the heart disease is the number one cause of death among survivors of breast cancer.

Researchers have found in a large U.S. study that elderly women who exercised regularly before onset of breast cancer are better protected from cardiac side effects of cancer treatment.

The study revealed that among more than 4,000 women diagnosed with breast cancer when most were in their 60s or older, those who got regular exercise in the five years before diagnosis were up to 37% less likely than more sedentary women to develop and die of cardiovascular disease in the decade after diagnosis.

Moreover the protection and the lower odds of heart disease and cardiovascular-related death later were proportional to the exercise they got before diagnosis.

In part, this may reflect women living long enough after a cancer diagnosis to develop other age-related health conditions like heart disease. But cancer drugs and radiation also can damage the heart’s structure and function, the authors note.

“Cancer is a stressor to the system. People that exercise prior to any sort of systemic stressor, whether its cancer or stroke, would do better if they were already pre-conditioned prior to this life-stressor,” said Dr. Tochukwu Okwuosa of Rush University Medical Center in Chicago, who led the study.

To see whether pre-diagnosis exercise was associated with post-cancer heart disease, the researchers analyzed data on 4,015 participants in the long-term Women’s Health Initiative study who’d been diagnosed with breast cancer. All were free of heart disease before their cancer diagnosis.

Okwuosa’s team looked at the women’s self-reported exercise history for up to five years before the breast cancer diagnosis. They also examined cardiovascular disease deaths over an average of 13 years post-cancer diagnosis as well as heart-disease related events over about eight years, including heart attacks, strokes, heart failure, peripheral artery disease and procedures to clear a blocked heart artery.

Overall, compared to women who did no exercise or very little, those who got light to moderate exercise weekly before diagnosis were 20% less likely to experience cardiovascular events in the follow-up period. Women who did the greatest amount of moderate-to-vigorous exercise were 37% less likely to experience these events.

The researchers saw similar trends for individual heart-related events and heart-disease deaths, but after adjusting for age and other factors, some of the differences were too small to rule out the possibility they were due to chance.

Among the study’s limitations is that exercise after breast cancer diagnosis was not analyzed, so its contribution to heart-related outcomes is unknown.

But past research suggests people who regularly exercise before cancer diagnosis are more likely to keep it up during and after treatment, the study team notes.

The study wasn’t designed to prove whether or how exercise before a breast cancer diagnosis protects against heart disease afterward, the study team acknowledges. But it is plausible that going into cancer treatment with a higher “reserve” of cardiovascular fitness makes patients better able to tolerate the heart toxicity of cancer drugs and radiation, they write.

“As more and more patients survive their breast cancer, cardiovascular disease is and will continue to become a major risk of morbidity and mortality for survivors,” Dr. Lindsay Peterson of Washington University School of Medicine in St. Louis, Missouri, and Dr. Jennifer Ligibel of the Dana Farber Cancer Institute at Harvard Medical School in Boston write in an editorial accompanying the study.