WEDNESDAY, Jan. 31 (HealthDay News) -- Even for the overweight, regular moderate exercise does not hasten or delay the onset of osteoarthritis of the knee in older individuals, new research reveals.

The finding undercuts the notion that exercise might have a protective effect against osteoarthritis. However, at the same time, it suggests that those already burdened with an elevated risk, such as overweight seniors, can safely remain active.

"There was fear that weight-bearing exercise among overweight people might put the very people who need it most at risk of getting knee arthritis and knee pain, but this study suggests that is not the case," said study author Dr. David T. Felson, chief of Boston University's Clinical Epidemiology Research Training Unit. "There shouldn't be any concern."

The findings are published in the February issue of Arthritis Care & Research.

According to the National Institutes of Health, osteoarthritis is the most common form of arthritis in the United States, affecting more than 12 percent of the population.

The painful degenerative joint disease is characterized by a breakdown of the shock-absorbing cartilage that shields bones where they contact joints. Osteoarthritis is more prevalent among the elderly, especially women, but it can also develop among younger men and women.

In their study, Felson and his colleagues tracked the exercise habits and incidence of knee osteoarthritis for almost 1,300 men and women in Massachusetts. The study lasted for more than a decade, with participants averaging just over 53 years of age at the trial's outset.

Initial activity surveys were completed in 1991 and 1992 to assess the types and intensity of regular exercise being practiced. In 1993 and 1994, and once again from 2002 to 2005, the researchers took knee X-rays and had participants fill out knee function questionnaires. Just over one-quarter of the participants had already developed some form of knee pain by 1993-1994.

The researchers found that most of the men and women said they walked regularly for exercise.

However, by measuring "joint space loss" -- an apparent indicator of knee cartilage loss -- they found that disease onset was neither positively nor negatively influenced by physical activity.

The lack of a relationship between osteoarthritis and exercise held up regardless of whether the individual walked less than six miles per week or more, or whether or not they worked up a sweat.

Far fewer (68) of the participants either ran or jogged, but even this form of exercise didn't appear to increase or decrease their risk for developing osteoarthritis. Osteoarthritis risk didn't rise or fall in connection with any other moderate level of activity, either, the researchers said.

This held true even for participants who were overweight. Even though such relatively out-of-shape individuals were already at a higher risk for developing osteoarthritis, routine exercise did not contribute to, or help reduce, their overall risk for the disease.

Felson said his team focused primarily on the effects of moderate, rather than aggressive, exercise. But the study showed that this type of moderate physical activity is safe for older Americans when it comes to osteoarthritis risk.

"I do think this is a case where the glass is probably more half full than it is half empty," said Felson, who is also professor of medicine and public health at Boston University's School of Medicine and School of Public Health. "Yes, there have been advocates who have suggested that regular exercise might be protective against knee osteoarthritis, and that doesn't appear to be the case. But, the good news is that exercise is safe for people who are older."

Dorothy Dunlop, a research associate professor with the Institute for Healthcare Studies at Northwestern University's Feinberg School of Medicine in Chicago, also accented the positive.

"I see the glass full and brimming over, because the literature is bursting with suggestions that moderate physical activity is beneficial in terms of pain and function improvement, and has cardiovascular benefits for all people with and without arthritis," she said.

Dunlop led a study, released earlier this year, that showed that seniors who were already coping with arthritis and who avoided exercise were twice as likely to lose their ability to perform basic tasks such as dressing, bathing, or cooking, compared with more active elderly.

"So, what this new study is telling me is that people can be encouraged to exercise without a concern that this will increase their risk of osteoarthritis," she said. "To me, it's a very important and positive finding which strongly supports physical activity."

More information

For additional information on osteoarthritis, visit the U.S. National Institutes of Health.