''The frequency of obesity is 54% higher among people with arthritis compared to those without,'' says Jennifer Hootman, PhD, an epidemiologist with the CDC.
She is the co-author of the report, published in the CDC's Morbidity and Mortality Weekly Report.
"That was higher than I thought [it would be]," she tells WebMD. "I thought it would be 30% or 40%."
An estimated 72.5 million U.S. adults ages 20 and older are obese; 50 million have arthritis, according to the report.
The CDC researchers wanted to evaluate how many people with doctor-diagnosed arthritis were obese compared to people who do not have arthritis. They analyzed data from the Behavioral Risk Factor Surveillance System (BRFSS) for the years 2003 to 2009.
Obesity and Arthritis: The Statistics
The BRFSS is a telephone survey conducted annually with adults from all 50 states, the District of Columbia, Guam, Puerto Rico, and the U.S. Virgin Islands.
Data on arthritis and obesity are collected in odd-number years.
Survey takers asked the participants if they had any diagnosis of arthritis. They asked about osteoarthritis and rheumatoid arthritis. Osteoarthritis, also called ''wear-and-tear'' arthritis, is more common than rheumatoid arthritis, which involves chronic joint inflammation. They also asked about gout, lupus, and fibromyalgia.
For each of the four years analyzed, the prevalence of obesity for the 50 states and D.C. was higher among adults with arthritis than those without.
In 2003, 33.2% of those with arthritis from all 50 states and D.C. were obese, while 21.4% of those without arthritis were.
By 2009, 35.2% of those with arthritis were obese, while 23.6% of those without were.
The number of states that had 30% or more of its residents with arthritis classified as obese rose from 38 in 2003 (including D.C.) to 48 in 2009.
The rise in obesity among those with arthritis increased enough to be considered significant from a statistics point of view in Puerto Rico and 14 states.
Those states are:
- New Mexico
- South Carolina
- South Dakota
- West Virginia
Arthritis and Obesity: Perspective
The finding that arthritis and obesity are linked is no surprise, says Patience White, MD, vice president of public health at the Arthritis Foundation. She reviewed the study findings for WebMD but was not involved in the research.
However, the magnitude of the effect of arthritis on obesity is surprising to her, she says.
"It's good to bring attention to this link," White says. By and large, she says, people are not aware of it.
Explaining the Link Between Obesity and Arthritis
Does arthritis lead to obesity, or does obesity lead to the arthritis?
"It could go both ways," Hootman says. "People have arthritis, their joints hurt, they don't exercise," she says. "We also know once someone has arthritis, obesity will make it worse."
From other research, Hootman says, it is known that obesity is one of the risk factors for osteoarthritis.
White agrees the link could go both ways. Those with arthritis may give up on trying to be active -- a mistake, she says -- and put on weight. The extra weight can worsen the arthritis by putting extra stress on the joints.
White tells those with arthritis who are overweight to focus on small amounts of weight loss. "For every pound you gain or lose it is like 4 pounds of pressure on your knee," she says. Losing just a few pounds can reduce the pressure and perhaps the joint pain, she says. Once the pain is reduced, it can be easier to resume regular physical activity.