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.
And the more exercise they got before diagnosis, the lower their odds of heart disease and cardiovascular-related death later.
The five-year survival rate for breast cancer in the U.S. is nearly 90%, the study authors note in JACC: CardioOncology, and heart disease is the number one cause of death among survivors.
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.
Okwuosa, a cardiologist, informed that she started studying the issue because of her own experience with cancer patients.
“What I was finding in the clinic was that those who used to exercise prior to receiving treatment tend to be less tired and less weak while going through treatment, and they recover faster after treatment,” said Okwuosa.
“We did not find any data in the scientific literature that examined this.”
To see whether pre-diagnosis exercise was associated with post-cancer heart disease, the researchers analysed data on 4,015 participants in the long-term Women’s Health Initiative study who had 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 analysed, 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.
“Finding strategies to help patients engage in recommended amounts of physical activity before and after a breast cancer diagnosis will be critical to improving outcomes in women with early breast cancer,” they write.