Giving people who are at high risk of developing Type 2 diabetes an existing diabetes drug, while recommending diet and exercise changes, reduces their chances of developing the disease by about two-thirds, Canadian researchers have found.

In Type 2 diabetes, weight gain, poor nutrition and lack of exercise reduce the ability of insulin, which is manufactured by the body, to control levels of sugar, producing a condition called insulin resistance.

More than eight per cent of people worldwide are at high risk of developing Type 2 diabetes because of poor glucose regulation.

Population health researcher Dr. Hertzel Gerstein of McMaster University in Hamilton and his colleagues randomly assigned more than 5,200 adults with poor glucose regulation to receive either a drug used for the treatment of Type 2 diabetes or a placebo every day for three years.

Among those taking the drug, called rosiglitazone or Avandia, 280 developed diabetes, compared with 658 in the placebo group.

Throughout the study, the researchers stressed the importance of a healthy diet and exercise for all participants.

Previous studies showed intensive exercise and weight loss can lead to similar beneficial effects as the drug, but few people are able to maintain that level of exercise and weight loss over time, the researchers said.

Balancing risk of side-effects

However, the risk of heart problems such as non-fatal heart failure was slightly higher in the drug group compared with the placebo group.

The heart failure was not severe and was reversible with medication, said study co-author Dr. Sonia Anand of McMaster University, calling it a "relatively minor complication."

In addition, people taking Avandia have shown liver toxicity and vision problems that need to be monitored. Reports of side-effects are expected to become more common as more people take the drug.

"Balancing both the benefits and the risks suggests that for every 1,000 people treated with rosiglitazone for three years, about 144 cases of diabetes will be prevented, with an excess of four to five cases of congestive heart failure," Gerstein's team concluded in Friday's issue of the journal The Lancet.

Public health experts consider the preventive benefits of the drug to be significant.

But people should not be told to take a costly pill when lifestyle changes could do the job and the drug puts them at risk for side-effects, said pharmacist Sana Sukkari of Burlington, Ont.

Diabetes specialists said patients too often can't or won't make the lifestyle changes that could prevent diabetes. They say the next step is to follow patients in the study longer to see if the benefits of Avandia continue after patients have stopped taking the drug.

The results were also reported Friday at the European Association for the Study of Diabetes meeting in Copenhagen.

The trial was funded by the Canadian Institutes of Health Research, as well as Sanofi-Aventis, GlaxoSmithKline and King Pharmaceuticals. Several of the study's authors reported ties to drug companies.