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Cholesterol-lowering drugs known as statins may be linked to an increased risk of diabetes in middle-aged and older women, according to a U.S. study – but researchers said the benefits of the drugs still make them valuable for people at risk.

The study, published in the U.S.-based Annals of Internal Medicine, found that among the thousands of women looked at, those who reported using any kind of statin at the start of the six- to seven-year study were nearly 50 per cent more likely to be diagnosed with diabetes than those not taking statins.

"Statin medication use in postmenopausal women is associated with an increased risk for diabetes mellitus," wrote Yunsheng Ma of the University of Massachusetts Medical School in Worcester, and his colleagues.

The group used data from the U.S.-based Women's Health Initiative, including more than 150,000 diabetes-free women in their 50s, 60s and 70s.

As part of that larger trial, some of the women were prescribed diet changes or took daily hormone therapy or vitamins, while others weren't told to change their diet or lifestyle.

At the start of the study in the mid-1990s, the women filled out health questionnaires that included whether or not they were taking statins, as well as information on other diabetes risks, such as weight and activity levels. The researchers then followed participants for six to seven years, on average.

In total, just over 10,200 women developed diabetes, with women who reported using any kind of statin – about one in 14 of the participants – 48 per cent more likely to be diagnosed with diabetes than those not taking statins. That was after considering other known diabetes risks.

Previous studies, mostly in men, have suggested a smaller 10- to 12-per-cent increase in diabetes among statin users, said Naveed Sattar, a metabolism and diabetes researcher at the University of Glasgow, who did not take part in the study.

Those numbers may be more accurate because they come from trials in which participants were randomly assigned to take a statin or not, which can better account for possible differences in groups of patients, he said, noting that this kind of observational study can't prove cause-and-effect.

Still, "broadly speaking, this kind of confirms that statins may well increase diabetes risk," Dr. Sattar said.

The reasons why remain unclear, but the effect of statins on the muscles and liver may lead the body to make slightly more sugar than it normally would, or cause users to exercise a bit less, he added.

While this means that a bit more caution may need to be taken in broad statin use, the benefits still outweigh the potential risk for people with heart disease, he and other experts aid.

Instead, statin users should try to reduce their risk of diabetes in other ways, such as by losing weight and getting more exercise, and should have their blood sugar regularly monitored.

"The conclusion still stands that, over all, those people who've got existing heart disease or have had previous strokes, they still would get vast benefit from statins," Dr. Sattar said.