arthritis prevalence study

Study Finds Many More U.S. Adults Have Arthritis Than Previously Thought

Arthritis might be far more common in the United States than previously thought, especially among adults younger than 65. That’s according to a new study published online in Arthritis & Rheumatology in November.

Researchers at Boston University School of Medicine (BUSM) undertook the study because they suspected the current estimate from the Centers for Disease Control and Prevention (CDC) – which puts the number of adults with arthritis in the U.S. at around 54 million – might be too low.

That estimate is based on a single question on the National Health Interview Survey (NHIS) that asks whether survey participants have “ever been told by a doctor or other health care professional that you have some form of arthritis, rheumatoid arthritis, gout, lupus or fibromyalgia?” (The CDC uses data collected by the NHIS to assess the nation’s health and the prevalence of health conditions.)

The Boston researchers developed what they consider a more accurate method for capturing the prevalence of arthritis, by factoring in two additional questions from the survey. One asks participants whether they’ve had joint pain or stiffness in the past 30 days, and the second asks whether the symptoms lasted three months or more. When the researchers analyzed the 2015 NHIS data, the most recently available at the time, using all three questions – doctor-diagnosed arthritis plus the two on self-reported joint symptoms – they found the number of people thought to have arthritis was 68 percent higher than the previously reported prevalence number.

Of more than 33,500 participants, 19 percent of men and 17 percent of women age 18 to 64 without doctor-diagnosed arthritis reported having joint symptoms; for men and women 65 and older, the proportions were 16 percent and 14 percent, respectively (numbers are rounded). Based on these findings, the Boston researchers calculated that around 30 percent of men and women in the U.S. ages 18 to 64 have arthritis, as well as 56 percent of men and 69 percent of women age 65 and older. In all, they say, that adds up to 91 million U.S. adults with arthritis – a large increase over the existing estimate of 54 million.

When reached for comment on the study findings, the agency said it is CDC policy not to comment on outside studies.

Caution with the Numbers

These new numbers must be viewed with some caution for several reasons. One caveat is that self-reports are often unreliable. Lead study author S. Reza Jafarzadeh, PhD, a researcher and assistant professor at BUSM, says they were aware that what people report on surveys may not be accurate and took measures in their analysis to account for that. He explains that the model used in the study “explicitly adjusts for the imperfect accuracy of each criterion.”

Jeffrey N. Katz, MD, a professor of epidemiology and environmental health at
Harvard T.H. Chan School of Public Health and rheumatologist at Brigham and Women’s Hospital, both in Boston, wasn’t involved in the study but wrote an editorial on it. Dr. Katz, who has coauthored other arthritis prevalence studies, says, “The work of Drs. Jafarzadeh and Felson moves our field a large step forward.…” He calls their adjusted prevalence estimates “sufficiently robust and concerning.…”

But Dr. Katz also points out a few of the limitations. For instance, the methods the researchers used to verify answers and then generalize to the larger population were based on information from a small subgroup of people, most of them white. The limited number of participants and their racial makeup mean the data may be less applicable to the NHIS respondents, who more closely reflect the racial/ethnic makeup of the nation as a whole. (Nearly 25 percent of the U.S. population is non-white, according to 2016 figures provided by the U.S. Census Bureau.)

Bei Wu, PhD, a professor in global health at NYU Rory Meyers College of Nursing and co-director of the Aging Incubator there, also urges caution, citing the issue of self-reporting. “We need to be cautious about the estimated prevalence, because pain as a symptom is not equivalent to having arthritis,” she says.

Still, Wu, who was not involved in the study, says it is interesting because it tries to avoid the pitfalls of basing disease prevalence on a single question about doctor-diagnosed disease. “Individuals with no health insurance and low income are less likely to see a doctor, and thus their disease is likely to be underdiagnosed,” she points out.

Other people excluded from the CDC’s estimate, as well as those of the Boston researchers’, are two groups known to have high rates of arthritis – people in nursing homes and those on active duty in armed forces – because the NHIS is limited to the “civilian noninstitutionalized population.”

Additionally, the current estimate excludes those who may possibly have arthritis, but not severe enough to warrant a trip to the doctor for diagnosis.

Beyond the Numbers

Arthritis is a leading cause of disability in the U.S., and the Arthritis Foundation says that while prevalence of arthritis is important, the exact figure doesn’t change the urgency of its mission. “Let’s not think about whether 91 million is perfectly accurate. Instead I think this tells us that the original numbers are conservative, and likely represent the floor and not the ceiling,” says Guy Eakin, PhD, Senior Vice President of Scientific Strategy at the Arthritis Foundation.

“This study represents significant progress in understanding the expansive reach of arthritis in our communities,” says Eakin, noting that even the current, lower estimate of arthritis prevalence shows the personal and societal costs of the disease are steep.

“If there are many more people out there who in fact do have arthritis, it should have a significant effect on how we think about the overall cost of arthritis. We need to consider the numbers we currently have, in terms of the medical burden of arthritis and the cost of care, as being conservative estimates,” Eakin says.

Says Jafarzadeh: “The impact of arthritis on public health is substantial in terms of health care direct costs and also disability and loss of productivity.”

Indeed, in a study published online in Arthritis Care & Research in September 2017, the CDC reports that total medical costs and earnings losses due to arthritis amounted to almost $304 billion in 2013 – about 1 percent of U.S. gross domestic product for that year. The earnings losses were slightly higher than medical costs.

Jafarzadeh says the method devised by him and co-author David T. Felson, MD, a professor of medicine at Boston University School of Medicine and of epidemiology at Boston University School of Public Health, isn’t intended to diagnose arthritis in individual patients. But he says the study may be useful for patients in several ways. For one thing, it may prompt doctors to pay more attention to arthritis in younger adults.

If the researchers are right, 30 percent of people aged 18 to 64 have joint disease. That finding is supported in part by other studies showing that the rate of joint replacement surgery is growing faster in younger people than older ones. “Arthritis should not be perceived as a condition that affects [only older adults] anymore,” Jafarzadeh says.

Says Dr. Katz, the idea that arthritis may be more prevalent than previously thought makes overall prevention – and prevention of worsening disease – more crucial than ever. And that begins with simple, inexpensive lifestyle changes that almost anyone can make.

Weight management is probably the most important preventive strategy we have,” Dr. Katz explains. It’s particularly relevant given that two-thirds of Americans are either overweight or obese, and people who are overweight/obese have arthritis at higher rates than those with BMIs in the “normal” range.

Other lifestyle factors are also believed to help prevent or slow progression of arthritis, including daily physical activity and eating a healthy diet.

In his editorial, Dr. Katz calls for “a policy agenda encouraging greater investment of scarce resources into the pathogenesis, prevention and treatment of arthritis conditions.”

Eakin, too, says more research dollars should be invested in the control and elimination of arthritis. “What our government puts into research really does not reflect the severity or breadth of this problem,” he says. “Even if we look at these new numbers and say there is a range of severity – ranging from the very impaired to those who have fewer symptoms that don’t affect them on a daily basis – we have to look at this extra 37 million people as being on the arthritis disease trajectory, who may not be severely affected today, but years down the road their symptoms may become debilitating and we should be concerned knowing there is no cure.”

Author: Linda Rath

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