Aging and obesity are the chief culprits behind this growing health problem, according to the US Centres for Disease Control and Prevention.
"The increase in arthritis definitely has to do with the aging of our population, but it's also potentially linked to the obesity epidemic," said the study's lead author, CDC epidemiologist Kamil Barbour.
The researchers found that almost one-quarter of US adults – or 52.5 million – have some form of arthritis. And the disease limits mobility for almost 10% of adults – 22.7 million.
The number of Americans with arthritis didn't surprise Barbour. "We expect 57 million Americans to have arthritis by 2030," he said.
The unexpected finding was the degree to which arthritis limits Americans' physical activity. "It actually exceeds our estimates," he noted. "We projected we would be at 22 million in 2020."
Obesity a strong link
Obesity could be the cause of this surge, Barbour said. More than one-third of Americans are obese, according to the CDC.
"We know that obesity is strongly linked to osteoarthritis, and knee osteoarthritis is one of the most prevalent conditions in the population," he said.
The researchers also found that about half of adults with heart disease or diabetes also had arthritis. For more than one-quarter of these adults, arthritis limited their activities, Barbour pointed out.
In addition, almost one-third of obese adults had arthritis, 15% of whom were physically limited by the condition, he added.
"This report confirms that arthritis is a huge public health problem," said Dr Patience White, vice president for Public Health Policy and Advocacy at the Arthritis Foundation and a professor of medicine and paediatrics at George Washington University School of Medicine and Health Sciences.
What is worrisome is that more people with arthritis also have limitations of their activity, she agreed. "This is really a warning; it's saying you really need to do something about this," she said.
Although you can't stop aging, you can decrease the impact of arthritis, White noted.
"The reason why the activity limitation has gone up for people with arthritis is because of obesity," she said. Losing weight and exercising are the keys to fighting the disease, added White.
A little weight reduction
The hand and the knee are the joints most commonly affected by osteoarthritis, White said.
"Just a little weight reduction and physical activity decreases osteo-arthritis of the knee and takes away your pain," she said. "It's amazing what just a little bit can do to stem the tide."
White noted that many people with knee arthritis will end up getting a knee replacement. "But that's not the answer," she said. "If you are obese, the outcome of a knee replacement is much worse."
According to Consumer Reports, a knee replacement can cost anywhere from $17 800 to $42 750, depending on where in the United States it's done. Most insurance, including Medicare, covers the procedure, but there are additional costs involved in recovery and rehabilitation.
"If you have a little bit of knee pain, you need to get active now, because you really can prevent this," White said.
For more information on arthritis, visit the Arthritis Foundation.