Arthritis symptoms diminish when obese mice exercise

Exercise relieved symptoms of arthritis in obese mice, even though they lost no weight from their efforts, a study finds.

Excessive weight has long been considered one of the culprits of osteoarthritis, since it puts additional strain on joints. While exercise has been shown in some studies to ease arthritis symptoms, others have found that for overweight and obese people, a fitness regimen can exacerbate the condition.

This study, published online Tuesday in the journal Arthritis & Rheumatism, found that although weight may heighten the risk of osteoarthritis, regular exercise could diminish joint problems by slowing its progression.

Researchers from Duke University worked with 20 8-week-old male mice, half of whom were fed a high-fat diet in which 60% of calories came from fat. The other half got their usual food, with 13.5% of calories from fat.

As expected, the mice on the high fat diet got pretty chubby; after 12 weeks they had a 55% increase in body mass and their body fat percentage rose more than three-fold. Researchers found evidence of osteoarthritis in the mice’s knees, such as markers for inflammation. They also found elevated glucose levels (an indication of prediabetes).

When the obese mice started running regularly on a wheel, changes started happening, despite the fact that they were still chowing down on that fatty diet and losing no weight: the inflammation reponse was disrupted and glucose tolerance improved.

“I don’t want to say exercise is turning off that inflammatory signal, it just impairs it,” said lead author Timothy Griffin in a news release. “This shows that if you are obese, it’s better to exercise. Sometimes pain can be a barrier to starting exercise, but if you overcome it, in the long term, it’s better.”