A study released in 2008 by a team of investigators from the Centers for Disease Control and Prevention (CDC) in Atlanta and the University of North Carolina at Chapel Hill discovered a much higher risk of knee osteoarthritis than experts had previously known. 

The study suggests that nearly 1 in 2 people will develop OA in a knee before age 85, with risk approaching 2 in 3 for people who are overweight or obese. 

Here's a look at the demographics of the osteoarthritis research group.

The study participants included 3,200 citizens of Johnston County, NC. Anyone who was over the age of 45 was eligible to join the study, whether they had arthritis or not. At the start of the JoCo study, in 1990, participants averaged 61 years of age. There were slightly more women than men; roughly 80 percent of study participants were white, and 20 percent were black.

Joanne Jordan, MD, PhD, professor of medicine and orthopedics at the University of North Carolina at Chapel Hill, and her team worked hard to recruit African-Americans because arthritis had not been well studied in that ethnic group.

“There was a real gap in racial disparities in what we knew,” Dr. Jordan said. “We wanted to know if there were differences in arthritis in blacks and whites and to see if there was a difference in prevalence between the two groups.

Most of the study participants were married and had at least a high school education. Nearly two-thirds were overweight or obese, a percentage that was higher than the national average at the time, but that now matches prevalence of obesity nationwide.

Many of the participants live in rural and suburban areas, and a fair number are farmers.