PHILADELPHIA – Statins, drugs used to lower cholesterol and reduce heart disease risk, aren't likely to raise or lower overall risk of common cancers when taken for more than five years, according to a new study.

Previous work has shown statins don't affect cancer risk over a short period, but this study investigated their impact on health over longer-term use, said study researcher Eric Jacobs, strategic director of pharmacoepidemiology at the American Cancer Society.

The finding "is reassuring, given that an estimated 24 million people use statins in the U.S. alone, and drugs can sometimes have unexpected long-term effects," Jacobs told MyHealthNewsDaily.

In the study, 133,255 men and women in the Cancer Prevention Study II Nutritional Cohort completed questionnaires about their lifestyles, including whether they took cholesterol-lowering drugs, most of which are statins. Researchers followed these people for 10 years to see if they developed cancer.

At the end of the 10-year period, 15,000 people developed cancer, according to the study. There was no difference in new cases of prostate, breast, colorectal, lung, bladder, renal cell or pancreatic cancer among people who took statins for five or more years compared with people who didn't take the drugs.

However, researchers observed a 20 percent to 30 percent lower risk of melanoma, endometrial cancer and non-Hodgkin lymphoma in people who took statins for five or more years, compared with people who didn't take the medications.

The study showed statins don't affect overall risk of common cancers for a period greater than five years, but more research is needed to see if taking them affects cancer risk over periods of 10 or more years, Jacobs said.

Researchers aren't sure why certain cancers seemed to be affected by statin use, Jacobs said, but they "do merit further study."

Past studies have shown that statins don't effect cancer risk in the short-term. A study presented earlier this year to the European Society of Cardiology Congress in Stockholm found that among 170,000 people from 26 previous trials, the rates of developing cancer were the same between people who took statins and people who didn't.

And a 2007 study in the journal Cancer Epidemiology, Biomarkers & Prevention found that prostate cancer risk did not seem to be affected by statin use for less than five years.

The study was presented here at the Frontiers in Cancer Prevention Research Conference, held by the American Association for Cancer Research.

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.