For years, doctors have been reluctant to advise elderly patients to lose weight based on evidence that weight loss later in life is associated with a higher risk of death. But a new study suggests the risk may not apply to seniors who intentionally exercise or change their diets to shed pounds.

Researchers at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., randomly assigned 318 older adults with knee arthritis to either a weight-loss or control group. Members in the weight-loss group were given either a new diet or exercise regimen, or both, to follow for 18 months. They lost an average of 10.5 pounds. Members in the control group lost an average of 3.1 pounds. (Most people lose some weight naturally as they age.)

But when researchers followed up with the test subjects eight years later, they found only 15 members of the weight-loss group had died, compared with 30 members of the control group.

“Overall, we found that there were far fewer deaths — half the number — in the group of participants that lost weight, compared to the group that did not,” said Kyla Shea, the lead author of the study. “It was an unusually strong and surprising finding.”

Doctors know that sudden, unexplained weight loss in older patients can be a sign of an underlying illness. It’s often the first clue that a senior is depressed or developing dementia. And observational studies that have tracked seniors over time have shown that those who lose weight are more likely to die in the following years.

For example, a University of Maryland study in 1999 found that elderly women of average size who lost weight over the course of the six-year study were four times more likely to die than women who either maintained their weight or gained a few pounds. The researchers conducting that study suggested that women shouldn’t try to achieve an ideal weight late in life.

But Dr. Stephen Kritchevsky, the geriatrician who oversaw the Wake Forest study, said previous research may have lumped together people who lost weight due to health problems and people who lost weight to improve their health, confounding the results.

“The data that people have been using has been unable to separate the cause and effect of the weight loss,” he said. “Our study suggests that the weight loss they’ve been studying may be the result of other health problems and not of intentional weight loss.”

Some previous studies have tried to get around the difference by asking individuals whether the weight loss was intended. But Kritchevsky said patients almost always say they’re trying to lose weight.

“So we have already a bias against weight loss in the elderly from a clinical perspective that’s sort of reinforced by observational data that flatter that bias,” he said. “What was needed was a trial of the topic to see what’s happening when people are actually randomized to lose weight or not.”

The researchers could not determine how weight loss helps extend lives but did note that weight loss in older adults has been shown to improve blood pressure, cholesterol and glucose levels. They also found that the benefits held up regardless of the age of the test subjects.

“I think when we’re getting into the older age range, what we’re really interested in is good functioning,” Kritchevsky said. “So we know that obese older people have problems with mobility, are at much higher risk for lower extremity pain, which is limiting of their function, are associated with diabetes and hypertension, and a number of other health problems.”

Current recommendations from the National Heart, Lung and Blood Institute, part of the National Institutes of Health, calls for seniors up to age 85 to lose weight if they have a body mass index of 30 or higher. (Body mass index, or BMI, is a ratio of weight to height.) Seniors with a BMI of 27 to 30 are advised to lose weight if they have any other weight-related health issue, including knee osteoarthritis, metabolic syndrome, low HDL cholesterol, high blood pressure or a history of heart disease.

Kritchevsky cautioned, however, that seniors who set out to lose weight should do so in a way that maintains muscle and bone mass.

“When you lose weight, you lose everything,” he said. “You lose bone, you lose muscle and you lose fat.”

Seniors can minimize the amount of bone loss associated with weight loss, he said, through resistance exercise such as lifting weights and by maintaining protein intake levels if they cut calories.

“Most people don’t eat that much excess protein anyway, so if they cut everything by 20 percent, they may actually become protein deficient and lose lean mass,” Kritchevsky said.

Bone loss, he said, can also be minimized through resistance training and by taking a calcium and vitamin D supplement.

Although the study was not large enough to determine the exact risk reduction associated with losing weight, the researchers said the analysis clearly showed there was no increased risk in doing so.

“This study puts to rest a lot of the unfounded concerns about how to address the epidemic of obesity among our older adults,” Kritchevsky said.