A study suggests that being overweight or inactive may increase a woman’s risk of developing fibromyalgia – a condition characterized by widespread muscle pain and fatigue.

The 2009 study also found that regular physical activity may be somewhat protective when it comes to muscle pain. Women in the study who reported exercising at least four times a week were about 30 percent less likely to develop fibromyalgia than inactive women.

Researchers at the Norwegian University of Science and Technology, in Trondheim, followed 16,000 healthy women for 11 years. The women were asked to record their weight and to report the frequency and duration of any weekly exercise.

Over the course of the study, 380 women said they had been diagnosed with fibromyalgia.

Being overweight, which was defined as having a body mass index, or BMI, over 25, increased a woman’s risk of developing fibromyalgia by about 70 percent compared with a woman who had a BMI under 25. 

But excess weight wasn’t the only factor that affected risk. Researchers found that exercise – or lack thereof – was also a powerful influence.

Women who reported being inactive, even if their weight was normal, had a 40 percent greater risk of developing the condition compared to those who exercised.

Those at highest risk of developing fibromyalgia, however, were those who were both overweight and inactive – a combination that roughly doubled their odds compared to normal weight women who exercised for at least one hour each week.

The study was published in the May 2010 issue of Arthritis Care & Research.

Bruce Solitar, MD, is a clinical associate professor of Rheumatology at NYU Langone Medical Center who specializes in connective tissue disorders and fibromyalgia.

He says the findings in this study are in line with other research suggesting that weight can play a role in fibromyalgia.

“I think the observations that patients who are heavy and patients who don’t exercise and are not in good physical shape are more at risk for fibromyalgia probably makes sense,” Dr. Solitar says.

But he says the study doesn’t say much about particular patients, so you don’t know if one group had more pain than another or what medications they were on.

He also says that while a high BMI and fibromyalgia are often connected, he doesn’t believe this study definitively shows which comes first.

“If you have a serious case (of fibromyalgia) and have a lot of pain, you are likely to be on medicine and a lot of the medicines lead to weight gain,” Dr. Solitar says.

“If you are in a lot of pain and you can’t exercise, you may be heavier than someone who exercises three times a week. So the observation may be 100 percent correct, that if you are heavier you are more likely to have fibromyalgia, but I don’t know if the cause and effect is out there yet.”

Even so, Dr. Solitar agrees that patients with fibromyalgia who are heavier should work vigilantly to keep their weight down and their exercise level up. But he says, take your time if you’re just beginning an exercise program.

“Many fibromyalgia patients, particularly those currently not exercising or in good physical shape, have to be careful how they start exercising,” Dr. Solitar says. “Take it slow. People have to be patient and build up their stamina.”