Arthritis is the leading cause of disability and pain in the United States and the impact on individuals is quite significant. The most common form of arthritis is osteoarthritis (OA), which often affects the knees, hips, and lower back. Rheumatoid arthritis (RA), an autoimmune disease, can lead to structural damage, deformity, and disability. About 75% of those affected by RA are women.

To get a closer look at prevalence and age-related trends of OA, RA, and other types of arthritis in the US, a study led by a researcher at Florida Atlantic University and collaborators, examined nationally representative data from 43,706 participants aged 20 years and older from the 1999 to 2014 National Health and Nutrition Examination Surveys (NHANES). NHANES is a program of studies from the Centers for Disease Control and Prevention designed to assess the health and nutritional status of adults and children in the US.

Results of the study, published in the Journal of Public Health, revealed some unexpected findings. While the prevalence of OA has more than doubled over time, the prevalence of RA has declined. In addition, even though obesity has been recognized as a risk factor for arthritis, the prevalence of obese people with all types of arthritis has decreased significantly.

Other findings show that the increase in OA prevalence was significant in both men and women; in non-Hispanic whites, non-Hispanic blacks, and Hispanics; and in people with high socioeconomic status. The decrease in prevalence of RA was more pronounced in men, non-Hispanic blacks, and participants with low income or those who were obese.

Researchers found that Hispanic and non-Hispanic blacks were less likely than non-Hispanic whites to have arthritis, possibly attributable to lack of adequate health care for correct diagnosis. Non-Hispanic blacks and Hispanics are more likely than non-Hispanic whites to use self-care or alternative or complementary medicine and are less likely to receive traditional medical care. OA was more common in older white women. Age-related degeneration and hormonal changes (lower estrogen levels associated with increased risk for OA pain in women) may explain this finding.

“The increase in OA with age is a consequence of cumulative exposure to risk factors and biological changes, such as oxidative damage, thinning of cartilage, or muscle weakness,” said JuYoung Park, PhD, lead author of the study and associate professor in the Phyllis and Harvey Sandler School of Social Work within FAU’s College for Design and Social Inquiry.

From 2010 to 2012, prevalence of arthritis was 22.7% and increased to 26.3% from 2013 to 2014. In the 16-year period, age-adjusted prevalence of RA decreased overall. The researchers surmise that it may be due to the introduction of effective drugs that have improved treatment regimens over the past 20 years and therefore decreased RA prevalence. However, during the same period, age-adjusted prevalence of OA increased in almost all subgroups.

“Given the health and economic burden of arthritis, understanding prevalence trends is of significant public health interest,” said Park, who has designed innovative research studies on the effects of chair yoga on OA. Initial results of her pilot study found significant reduction of pain and mobility in the study participants. “Because of these burdens, developing cost-saving and effective treatments are necessary to minimize arthritis symptoms, maximize functional capacity, reduce disability, and moreover, improve the quality of life for the more than 350 million people worldwide who are affected by arthritis.”