DENVER (The New York Times News Service) -- It seemed to Margie McCandless that she was destined to have diabetes.

Her mother nearly lost her eyesight because of the disease.

McCandless had seven diabetic aunts and uncles, and one uncle had to have his leg amputated because of the disease.

Sugar levels in McCandless' blood pegged her as pre-diabetic.

But the 74-year-old widow from the Denver suburb of Broomfield, who participated in a 10-year study through the Colorado School of Public Health, managed to stave off diabetes -- even lowered her blood-sugar levels to normal -- through major lifestyle changes.

The landmark study, results of which are published Thursday in The Lancet medical journal, found that people at high risk for diabetes cut their chance of developing the disease by 34 percent through weight loss, exercising five days a week and reducing fat intake. People age 60 and older cut their risk by almost 50 percent.

The impact of weight loss and exercise was more profound than the most commonly prescribed drug for diabetics, which reduced the risk of the disease by 18 percent during the 10-year study.

The scope of the research, which included 3,234 overweight people at 27 sites across the country, was the most intensive to date on diabetes.

Particularly significant, researchers said, was the discovery that weight loss, healthy diet and exercise can reduce the risk of the disease for a decade, not just a few months or years.

"If people would just do it, it would work," said Dr. Richard Hamman, the study's vice chair and dean of the School of Public Health at the University of Colorado Denver Anschutz Medical Campus. "The problem is, it's not that easy to do."

Study participants -- most of them obese and all of them with impaired glucose tolerance found through blood tests -- were asked either to take a drug called metformin, were given placebo pills or were told to make major lifestyle changes, including losing 7 percent of their body weight. A 200-pound person, for example, was told to lose 14 pounds.

Nutrition and exercise coaches asked participants in the lifestyle-modification group to exercise 30 minutes, five days per week. Most chose walking. They also were given advice on healthy eating -- limit fried foods and fatty meats, switch to chicken without skin, put less butter on the toast.

For McCandless, it was cutting back on Hershey kisses and chips, plus participating with a group of women for water aerobics. She lost 30 pounds, learned to snowshoe, and next week, she's headed to the Galapagos Islands to snorkel.

"I want to be alive for my daughter and son who are diabetic and have kids," said McCandless, who now weighs 188 pounds. "I want to be a great grandmother."

Studies in Finland and China also have determined that lifestyle changes reduce the risk of diabetes.

The American study, though, included a more diverse group of patients, including races disproportionately affected by type 2 diabetes -- African-Americans, Latinos and Native Americans.

About 24 million Americans have diabetes, most of them type 2 -- which is linked to obesity, inactivity and family history. The prevalence of diagnosed diabetes has more than doubled in the last 30 years.

"The diabetes pandemic continues," said Dr. David Nathan at Massachusetts General Hospital, study chair. "It's getting worse, owing to the toxic lifestyle we are leading -- too much food, too much weight gain."

The study also found that people who lost weight and ate less fat had healthier blood pressure and triglyceride levels.

Dr. Richard Abrams, an internist at Rose Medical Center in Denver who has specialized in diabetes, but was not part of the study, said the research "has enormous implications" for people at risk of diabetes.

"With attention to exercise, diet and weight control, this disease that is epidemic in our society and accounts for staggering amounts of loss of health, disability and cost, can be prevented," he said.

"This is information that will be of great value to all primary care physicians and public health officials."

The study was funded by The National Institutes of Health. Many of the participants were referred by Kaiser Permanente after diabetes screening.

Copyright 2009 The New York Times News Service. All rights reserved.