Tightly controlling blood sugar in people with diabetes doesn’t relieve inflammation that can lead to heart disease, a new study shows.

A study of 500 people newly diagnosed with type 2 diabetes shows that a drug called metformin and a once-daily injection of insulin are both effective in controlling blood sugar levels. But the drugs, either alone or in combination, don’t lower levels of three markers of inflammation any more than a placebo does, Aruna Pradhan, a cardiologist at Brigham and Women’s Hospital in Boston, and colleagues report in the Sept. 16 Journal of the American Medical Association.

Blood sugar control is important for protecting small blood vessels from damage that can lead to eye disease, kidney disease and nerve damage, says Steven Nissen of the Cleveland Clinic in Ohio. Previous studies have yielded mixed results, leaving it uncertain whether keeping blood sugar levels in check can fend off cardiovascular disease, heart attacks and stroke.

Pradhan’s team reasoned that if diabetes drugs lower measures of inflammation, then the drugs might also ward off heart disease and other long-term consequences of inflammation. But the team found that 14 weeks of treatment with metformin, with the once-daily injection of insulin, in a form called insulin glargine, or with a combination of both drugs was no better than a placebo for reducing three markers of inflammation, proteins known as high-sensitivity C-reactive protein, IL-6 and sTNFR2. The results may help explain why some large clinical trials didn’t show that lowering blood sugar prevents cardiovascular disease, Pradhan says. But she emphasizes that her study was short-term and may not show long-term benefits of the drugs.

“It’s a nice little study,” says Hertzel Gerstein, a diabetes researcher at McMaster University in Hamilton, Canada. “But its clinical relevance is totally uncertain today.” He points to one long-term study that showed that people who controlled their diabetes with metformin had a reduced risk of dying from any cause, including heart attacks.

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Found in: Body & Brain