A government report found that the number of American adults with arthritis is rising, and along with it, so is the disabling impact of the disease.

The 2010 report from the Centers for Disease Control and Prevention (CDC) shows that the number of people older than age 18 with doctor-diagnosed arthritis has climbed from roughly 46 million to 50 million over the last four years.

That increase is in line with previous predictions that cases of arthritis would rise with the aging of the population.

The report, containing data from 2007 through 2009, says 22 percent of the population has arthritis, which costs our economy $128 billion a year.

What has experts most concerned, however, is the sharp increase in the percentage of people with arthritis who say that they have to skip some everyday activities – things like climbing stairs, grocery shopping or jogging – because of their disease, which can cause severe pain and limited mobility.

“The one thing we know is arthritis prevalence is growing at about one million people a year, but the surprising finding was the number of adults with activity limitation is growing faster than we expected,” says Jennifer Hootman, PhD, an epidemiologist with the CDC’s Arthritis Program.

Some 21 million adults, or nearly 1 in 10, say arthritis limits their daily activities.

That’s two million more than the CDC had previously estimated and not far off from the projection of 25 million that wasn’t expected until 2030.

“We’ve still got a long time to go before 2030 and we’re almost there [to the 25 million mark],” Dr. Hootman says. “It’s growing at a much faster pace than we had projected.”

Activity limitation is defined as any kind of regular activity that someone wants to do but can’t because of arthritis and its symptoms.

“I think people haven’t understood what arthritis being the most common cause of disability means. It means that people lose independence and that is a powerful thing and I think we are looking at it starkly when we see that people are having activity limitations,” says Patience White, MD, vice president for public health at the Arthritis Foundation and professor of medicine and pediatrics at George Washington University School of Medicine in Washington, D.C.

As for what’s behind the increased activity limitations, the CDC believes it’s a combination of two things – age and obesity.

“We expected to see some of this increase because of the aging of the population,” Dr. Hootman explains. “But this is more than we expected in activity limitation and that’s probably, although we can’t directly link it, that’s probably related to the increase in high prevalence of obesity.”

The CDC’s report says about 1 in 3 people who are obese have arthritis. This is almost double prevalence of arthritis in normal-weight people.

“The link that obesity can worsen your arthritis and cause arthritis is a total and utter surprise to people,” Dr. White says.“They don’t know that. They think arthritis is just an old person’s disease. They don’t know there is something you can do about it.”

Studies have shown that obesity dramatically increases the risk for arthritis, though researchers aren’t sure why. Some evidence has pointed to the idea that force of carrying extra weight damages joints, while other studies have suggested that inflammatory chemicals released by fatty tissue may be to blame.

Whatever the mechanism, experts say the bottom line is that arthritis is not an inevitable consequence of aging.

Dr. Hootman says people need to understand that activity limitations can be prevented or improved through weight loss, physical activity, and what’s called self management education – where people are taught to develop goals and learn ways to manage their arthritis symptoms day to day.

“Those things all improve pain and function and that should translate to reduced activity limitations,” Dr. Hootman says.

Dr. White says these new numbers remind the public health community there’s still much work to be done.

“We can’t change age,” she explains. “But can we have them age in a more healthy manner? You bet.”

“What they don’t know is there are ways to be active. Their assumption is moving hurts me; I shouldn’t do something that hurts me. So we have a huge job to get people to understand that actually, movement helps,” she continues. “I think we have to work even harder to get people moving and doing the kind of activities that are going to make their life better.”