A new study on breast cancer shows a link between radiation treatment and later risk of developing heart problems.

For every gray (Gy) of radiation exposure to the heart, the risk of major heart events rose by an average of 7.4 percent--with no apparent threshold, says Sarah Darby, of the Clinical Trial Service Unit in Oxford, England, which conducted a study of 2,168 breast cancer survivors in Sweden and Denmark. However, the rate varied with time, with a 16.3% greater risk in the first 5 years after exposure and 15.5% in the second 5 years. The rate fell to 1.2% in the second decade and rebounded in later years to 8.2%.

Women with pre-existing heart risk factors were more vulnerable to later coronary problems, doctors said, nothing that American women receive less preventive care than their European counterparts.

The increased risk was greatest during the first five years after radiation treatment but remained for at least two decades. Women with pre-existing cardiac risk factors experienced an even greater risk, as reported by ABC News. While radiation provides value for breast cancer patients, "clinicians may wish to consider cardiac dose and cardiac risk factors as well as tumor control when making decisions about the use of radiotherapy for breast cancer," Darby and colleagues reported in today's issue of the New England Journal of Medicine.

Investigators say doctors must take extra measures to protect women from cardiac risk, watching for hypertension, diabetes and high cholesterol. Following radiation therapy for breast cancer patients, doctors should pay attention to women's heart health, says Dr. Jean-Bernard Durand of the MD Anderson Cancer Center in Houston.

"Follow their cholesterol, watch for diabetes, manage their blood pressure - all those things can be done to lower their risk of a cardiovascular event," he told Medpage Daily.

The study was supported by Cancer Research UK, the British Heart Foundation, the U.K. Medical Research Council, the European Commission, the U.K. Department of Health, the British Heart Foundation Centre for Research Excellence, and the Oxford National Institute for Health Research Biomedical Research Centre. The New England Journal of Medicine said investigators reported no financial conflicts of interest in the study.