(The New York Times News Service) -- Seniors who engage in some form of minimal exercise at least three days a week can cut their risk of developing Alzheimer's and other forms of dementia by as much as 30 percent to 40 percent, a new study reveals.

Even better, the findings applies to everyone in their later years, not just those already in great physical shape.

"Regular exercise at least three times a week could delay the onset and reduce the risk of developing Alzheimer's, and the more frail a person is, the more he or she is gong to benefit from exercise," said lead author Dr. Eric B. Larson, director of the Group Health Cooperative's Center for Health Studies in Seattle.

"So use it even after you start to lose it -- that's the banner headline," he added. "There's a tendency to sit down and do nothing when you start to lose function, but the opposite is probably exactly what's in order if you want to stave off Alzheimer's disease."

Between 1994 and 2003, Larson and his team assessed the health, physical and mental function, and lifestyle characteristics of 1,740 men and women over the age of 65.

All the patients were members of a Seattle-based health-maintenance organization. None had been diagnosed with dementia or were living in a nursing home at the start of the study.

Every two years, the researchers used examinations and in-person interviews to evaluate participants' weekly exercise routines; physical abilities such as walking, standing, balancing and gripping; memory, attentiveness and concentration skills; and smoking, drinking and dietary supplement habits.

Reporting in the Jan. 17 Annals of Internal Medicine, they noted that 107 participants went on to develop Alzheimer's within six years of the study. Another 51 patients developed other forms of dementia, while 276 participants died during the course of the study.

Those who had been engaging in regular exercise when the study began -- defined as 15 minutes of physical activity at least three days a week -- had a 32 percent lower risk of developing dementia than those exercising less than three days a week.

Exercise might not eliminate the chance of developing Alzheimer's or other forms of dementia altogether, the researchers noted. However, physical activity may help delay dementia onset by a number of years, they said.

Walking, hiking, bicycling, aerobics, calisthenics, swimming, water aerobics, weight training and stretching were all considered valid exercise activities. However, the authors did not measure exercise intensity, and physically taxing habits that had been conducted at the workplace or while completing non-leisure chores were also not assessed.

Other factors, such as educational achievement, alcohol consumption, smoking and dietary supplement use did not affect dementia risk, the study found.

Seniors who are in the worst physical shape have perhaps the most to gain from routine activity. According to the study, regular exercisers who had been evaluated as among the most physically weak at the start of the study experienced even more of a reduction in dementia risk than their more physically fit peers.

Larson and his colleagues called for future studies to explore the intensity and duration of exercise that would best improve circulation and oxygen delivery while reducing brain cell loss -- all of which they suspect accounts for the resulting drop in dementia risk.

"Alzheimer's disease is one of the conditions that people fear the most about getting old," said Larson. "Most people would like to live longer if they don't get Alzheimer's disease. And from the general public health point of view, knowing that this benefit exists might motivate people to make the behavior change to exercise regularly. This is a kind of underused treatment, if you will -- and it has many benefits beyond preventing Alzheimer's disease."

Greg M. Cole is a neuroscientist with the greater Los Angeles VA Healthcare System and the associate director of the Alzheimer's Disease Research Center at the University of California, Los Angeles. He expressed great enthusiasm for the study.

"I've been waiting for somebody to determine whether or not exercise can affect the onset of Alzheimer's," he said. "It's critically important, and it fits in well with what we already know."

"Reducing cholesterol with statins, reducing high-saturated fat intake, increasing mega-fatty acid intake, lowering blood pressure -- controlling all those factors seems to reduce our risk for Alzheimer's," he added. "And exercise now appears to be another one of those things. And it's really doable. People can apply it directly. So this is really great."

Copyright 2006 The New York Times News Service. All rights reserved.