Cholesterol-lowering drugs called statins, which have been shown to lower a person’s risk for heart attack, can also slightly increase a patient’s risk for developing diabetes, particularly at higher doses, new research shows.

The findings, based on new analyses of five clinical trials involving 32,752 patients, raise new questions about how much we really know about the long-term effects of statins, which are the most widely prescribed drugs in the United States. The focus on the link between statins and diabetes comes at a time when some medical experts and pharmaceutical companies have pushed to broaden the use of the drugs beyond the 40 million at-risk patients who already use them to healthy people who would take the drugs for prevention of heart disease.

Doctors cautioned that patients should not overreact to the diabetes news, saying that the increased diabetes risk is very small, and that the benefits of statin therapy still far outweigh any side effects.

“I don’t think it’s very clinically important,” said Dr. Steven E. Nissen, chairman of cardiology at the Cleveland Clinic, who consults with drug companies that make statins but requires his fees be donated to charity. “What I worry about here is that people will read this story and say, ”˜I don’t want to get diabetes so I’m going to stop my statin,’ and then they have a heart attack.”

Last year, the medical journal The Lancet published an analysis of major statin trials involving 90,000 patients that showed statin users had a 9 percent higher risk of developing diabetes than those who didn’t take statins. But questions remained about whether the effect was real or something that may have just been due to chance.

However, the latest analysis, published today in The Journal of the American Medical Association, makes the strongest case yet that statins can trigger diabetes in some people. The report focused on differences in diabetes risk among moderate-dose and high-dose statin users, and found that those taking high doses had a 12 percent higher risk of developing diabetes compared to moderate-dose users. That translates to a 20 percent overall increased risk of diabetes for high-dose statin users, compared to those who don’t take the drugs, according to the study’s senior author.

Even so, medical experts, including the study authors, argued that while more study is needed to understand the diabetes link, the increased risk doesn’t eclipse the strong health gains achieved with statins, which in some studies have reduced heart attack and stroke risk by half.

Based on the data in the study, a total of 498 people would need to take a statin before triggering one extra case of diabetes. By comparison, just 155 people would need to take a statin to prevent one heart attack.

“The net benefit favored the statins overall,” said Dr. Kausik Ray, professor of cardiovascular disease prevention at St. George’s University of London and senior author on the paper. Dr. Ray says he has consulted for drug companies that make statins.

Exactly how statins may increase diabetes risk isn’t entirely clear, though animal studies suggest that statins can increase muscle resistance to insulin, resulting in higher levels of circulating blood sugar. Dr. Kausik notes that the patients in the studies were diagnosed with diabetes because of elevated blood sugar levels, but that the long-term consequences of higher blood sugar levels triggered by statin use aren’t known.

“Diabetes is defined by blood glucose levels, but none of us are absolutely certain if this is going to carry the same risk as if you traditionally developed diabetes,” Dr. Kausik said.

In addition, Dr. Nissen says the statins don’t cause blood sugar to shoot up rapidly but instead can slightly elevate blood sugar enough to push borderline patients across the threshold into diabetes.

“It doesn’t take much to tip a few people over that boundary to the point where we call them diabetic,” said Dr. Nissen. “We can’t dismiss it, but I also don’t want to scare people who need these drugs. They are the best thing we’ve got going to prevent coronary disease events.”