More than 52 million Americans older than 18 say they have doctor-diagnosed arthritis – and nearly half of them say it limits their ability to work or perform everyday activities, according to a new report issued today by the Centers for Disease Control and Prevention (CDC), in Atlanta.

"This is a serious disease, and the rate of disability is of near-epidemic proportions, so something must be done," says Ann M. Palmer, president and CEO of the Arthritis Foundation. She notes that at present, more than one in five Americans – 22.7 percent – has arthritis, and the numbers are expected to rise.

The CDC findings, published in the November 8 issue of the Morbidity and Mortality Weekly Report, are based on annual surveys taken between 2010 and 2012; they show an increase of nearly one million people per year with arthritis. The researchers say that the increase – from 49.9 million since the last report based on 2007 to 2009 surveys – is in line with earlier projections, and is mostly due to an aging population. By 2030, 67 million U.S. adults are expected to have arthritis.

What researchers didn't expect is the large number of people whose daily functioning is currently affected by arthritis. Nearly 23 million adults – almost half of all people with arthritis and almost 10 percent of the entire U.S. adult population – report arthritis-related limitations on activities such as bending, climbing stairs or walking more than short distances. At this rate of growth, the number of people with arthritis-related limitations is expected to exceed the 25 million projected for 2030.

“We were surprised at the finding that 9.8 percent of the population has [arthritis-related] activity limitations,” says lead study author Kamil Barbour, PhD, an epidemiologist in the CDC’s Arthritis Program. “[Earlier studies] had projected that we would reach 22 million people in 2020, and we are already at 22.7 million. We did not expect to exceed that projection so quickly. But that projection was based only on the aging of the population and didn't take comorbidities such as obesity into account.”

Patience White, MD, the vice president for Public Health Policy and Advocacy for the Arthritis Foundation, also points a finger at obesity.

“It is not known exactly why the increase in arthritis-associated limited activity has increased more than the CDC projected, but many speculate it is secondary to the obesity epidemic. The relationship between obesity and arthritis is closely linked,” she says.

The CDC researchers based their findings on the results of the National Health Interview Survey (NHIS), an annual, in-person survey of the health and habits of American adults. The researchers combined data collected from almost 95,000 people during the course of three years – 2010 to 2012 – and categorized responses according to sex, age, race, education level, body mass index, physical activity and diagnosed heart disease, and diabetes. Arthritis was defined as doctor-diagnosed osteoarthritis, rheumatoid arthritis, gout, lupus or fibromyalgia.