Older women who’ve used calcium channel blockers for 10 years or longer may face a much higher risk of breast cancer.

Antihypertensive drugs used to lower blood pressure have made a huge impact on the lives of millions, and calcium channel blockers are among the most popular of these medications. Though these drugs are lifesavers in one respect, for older women, taking calcium channel blockers may create additional complications.

New research published in JAMA Internal Medicine provides evidence to support the long-suspected link between calcium channel blockers (CCBs) and breast cancer in postmenopausal women.

The study, run by researchers at the Fred Hutchinson Cancer Research Center in Seattle, found that prolonged use of calcium channel blockers led to a significantly higher risk of breast cancer, which means women with hypertension may want to consider alternative methods of reducing their blood pressure.

In the study, women ages 55 to 74 were divided into three groups: those with invasive ductal breast cancer, those with invasive lobular cancer, and those with no cancer to serve as controls. The women were asked about their medical histories, including medication use.

The researchers found that taking CCBs for at least 10 years was associated with increased risks of both ductal and lobular breast cancer. The researchers found no increased risk associated with the use of diuretics, beta-blockers, or angiotensin II antagonists.

This study was observational, so the results suggest a connection between CCB use and breast cancer but do not prove it, as in a clinical trial. And medical experts are still not sure precisely why CCBs may increase breast cancer risk.

According to the study, one reason might be that calcium channel blockers impede apoptosis, or programmed cell death. (Apoptosis is crucial for regular cell development.)

More research needs to be done to determine whether there is any difference in risk between short-acting CCBs and long-acting formulations, and if the length of time a patient takes these medications has any impact on her cancer risk.

The study authors explain: “Long-term CCB users will be accumulating in the large databases that are often used for post-marketing surveillance of medications…If increased breast cancer risks are observed in other studies like that, then mechanistic studies to identify how CCBs increase breast cancer risk would be important.”

Because high blood pressure is so common, antihypertensive medications are widely prescribed in the U.S. And as the study notes, many women take these medications for the rest of their lives once prescribed.

While this is just one observational study, the quality of the study, along with other substantiating research, shows that the risks of using CCBs after menopause is a valid concern. In a related commentary, Patricia F. Coogan, Sc.D., of the Slone Epidemiology Center at Boston University gave her reasons for supporting the study, with some caution:

“Given these results, should the use of CCBs be discontinued once a patient has taken them for 9.9 years? The answer is no, because these data are from an observational study, which cannot prove causality and by itself cannot make a case for change in clinical practice. Should the results be dismissed as random noise emanating from an observational study? The answer is no, because the data make a convincing case that the hypothesis that long-term CCB use increases the risk of breast cancer is worthy of being pursued.”

The verdict may not be clear cut, but always be sure to consult with a doctor before starting any new drug regimen, especially after major life changes, such as menopause.