For people with osteoporosis, exercise may encourage stem cells to become bone

Numerous public health authorities recommend that osteoporosis patients exercise as a way to build both bone and muscle, and now a seminal study has demonstrated that this skeleton-strengthening effect may be due to the way that physical activity activates certain stem cells.

Published in the Journal of the Federation of American Societies for Experimental Biology, the report announced that mesenchymal stem cells may ultimately generate bone cells or fat cells, depending on the amount of exercise that the body experiences during their development.

A team of Canadian researchers from Ontario's McMaster University came to this conclusion after subjecting laboratory mice to differing levels of physical activity over a 10-week period.

Scientists first measured blood markers of bone turnover and fat production in a group of selected rodents. Then, the team put half of the mice through a one-hour treadmill exercise three times a week.

Researchers noted that this is not an exceptionally large amount of activity, but that it is enough to affect the level of blood cells being produced in newly formed bone tissue - specifically, in the bone marrow, where mesenchymal stem cells generate new tissue.

After 10 weeks, investigators found that the mice that regularly exercised displayed more markers of bone turnover. Furthermore, the team used tissue samples to determine that the active mice converted more of their mesenchymal stem cells to bone than their sedentary counterparts.

The latter tended to see their mesenchymal stem cells converted largely into adipose cells.

"The interesting thing was that a modest exercise program was able to significantly increase blood cells in the marrow and in circulation. What we're suggesting is that exercise is a potent stimulus - enough of a stimulus to actually trigger a switch in these mesenchymal stem cells," co-author Gianni Parise said.

He and his colleagues added that this study is yet another piece of evidence pointing to the cellular benefits to be derived from regular exercise.

For people with osteoporosis or low bone mass, getting regular weight-bearing exercise is vital for the creation of new bone minerals.

The National Osteoporosis Foundation (NOF) emphasizes that people with osteoporosis must make it a point to exercise regularly. The organization specifies that at least 30 minutes of every day should be dedicated to low-impact weight training and muscle-building activity.

Putting periodic strain on load-bearing bones and muscles encourages them to create new cells, which is critical for people with bone loss. The NOF states that even individuals who have suffered an osteoporosis-related fracture should start getting regular physical activity again as soon as is clinically advisable.

It cautions that, for these patients, high-impact exercise may increase the risk of further fractures. This effectively eliminates activities like running on a treadmill (as the laboratory animals did in the study), dancing, jumping rope or playing tennis.

The NOF recommends that individuals pursue weightlifting, swimming, stretching, yoga and water exercises.

By doing so, they may encourage their mesenchymal stem cells to produce tough new mineral deposits, rather than generate additional, largely unnecessary fat cells.