NEW YORK (Reuters Health) - For almost 7 million American workers, arthritis keeps them from doing their job at peak performance, researchers estimate based on data from the 2002 National Health Interview Survey.

As part of the survey, more than 31,000 working-age adults were asked whether they had doctor-diagnosed arthritis and whether arthritis or joint symptoms limited their ability to work or the type or amount of work that they engage in.

Results suggest that arthritis affects roughly 18 percent of adults, or 23.4 million people, between the ages of 18 and 64. Of those with arthritis in this age group, nearly 30 percent report work limitations due to arthritis, a figure that corresponds to 5.3 percent of the adult population, or 6.9 million people.

According to a report in the journal Arthritis & Rheumatism, arthritis-attributable work limitation is most common among people aged 45 to 64 years (10.2 percent), women (6.3 percent), non-Hispanic blacks (7.7 percent), people who did not finish high school (8.6 percent), and those with annual incomes below $20,000 (12.6 percent).

Kristina A. Theis of the Centers for Disease Control and Prevention, Atlanta, and colleagues also note in their report that adults with arthritis-related work limitations had "multiple indicators of poor physical health and function." They were often overweight, suffered joint pain and reported frequent doctor's visits.

The indirect costs of arthritis have recently been estimated at roughly $35 billion. Therefore, "protecting workers from disability, injury, and prolonged negative effects of illness makes simple social and economic sense," Theis and colleagues write.

They also note that several arthritis self-management programs from the Arthritis Foundation have been shown to reduce physical and functional limitations, decreasing pain and delaying disability due to arthritis. These include the Arthritis Foundation Self-Help Course, the Arthritis Foundation Exercise Program and the Arthritis Foundation Aquatics Program.