MONDAY, Feb. 6 (HealthDay News) -- When it comes to the treatment of type 2 diabetes, the first line of defense is lifestyle changes such as losing weight and exercising more often.

But, if those lifestyle changes don't get blood sugar levels under control, the American College of Physicians (ACP) recommends the drug metformin as the first oral treatment that should be given.

If metformin alone can't control blood sugar levels, the ACP advises combining metformin with another blood-sugar lowering medication. But, the evidence isn't yet strong enough for the doctor's group to recommend one medication over another for combination therapy.

"Most diabetes medications do lower [blood sugar], but metformin is more effective with fewer side effects. And, the cost is less," said Dr. Amir Qaseem, director of clinical policy at the American College of Physicians, and the lead author of the new guidelines.

However, the ACP is recommending that metformin only be prescribed after someone has tried to change his or her lifestyle, he added.

"Diet, exercise and weight loss are so important in controlling type 2 diabetes. You can't just give pharmaceutical agents and not have lifestyle changes," Qaseem said.

The new guidelines are published in the Feb. 7 issue of the Annals of Internal Medicine.

Type 2 diabetes is a disease that causes high blood sugar levels. Over time, this can lead to blood-vessel damage in the eyes, kidneys, heart and nerves. Almost 26 million Americans have diabetes, and as many as 95 percent of those have type 2 diabetes, according to the new guidelines.

"Diabetes is a really important health-care issue in this country. It's a major cause of morbidity and mortality, and the prevalence of the disease is going up," Qaseem said.

Obesity and a sedentary lifestyle are significant risk factors for type 2 diabetes, although not everyone who has the disease is overweight.

There are currently 11 different classes of medications approved by the U.S. Food and Drug Administration for the treatment of type 2 diabetes, according to the guidelines. These medications work by lowering blood sugar levels.

To come up with the new guidelines on oral diabetes treatments, the reviewers looked at data for each available class of medication to assess how effective it was in lowering blood sugar, cholesterol and weight. They also looked at how much each medication was able to reduce the risk of complications from type 2 diabetes. And, they reviewed the safety of each type of medication.

They found that metformin was the most effective in lowering hemoglobin A1C (HbA1C) levels. HbA1C levels are a measure of long-term blood sugar control, estimating average blood sugar levels over several months.

The researchers also found that combination therapy with two drugs was more effective at lowering HbA1C than therapy with just one agent. However, when comparing different combination therapies, no particular combination stood out as superior to the others.

Metformin also appeared to be the most effective medication for lowering levels of LDL (bad) cholesterol, according to the guidelines. Metformin also seemed to be more effective at preventing all-cause mortality and heart disease.

Dr. Joel Zonszein, director of the clinical diabetes program at Montefiore Medical Center in New York City, said he would recommend starting medication along with lifestyle changes, instead of waiting to see if lifestyle medications work or not.

"Lifestyle changes fail in the majority of people. Why wait to start treating them? There should not be inertia. If you're more aggressive early in the disease you may be able to protect some of the beta cells," he said. Beta cells are cells in the pancreas that produce insulin, a hormone needed to metabolize carbohydrates in food.

Zonszein also said that many of the studies used to develop the new guidelines were short-term studies, often sponsored by drug manufacturers. He said to really know what treatments are best, longer-term studies are needed, as are studies that look at different combinations of diabetes medications.

He said he also would have liked the guidelines to address the use of cholesterol-lowering medications and blood-pressure lowering medications, as these are common problems seen in people with type 2 diabetes.

More information

The American Diabetes Association has more information on the types of oral medications available for type 2 diabetes.