AS may be more common than was once thought. Studies show it affects an estimated 1 out of every 200 adults in the US, which comes out to about 1.1 million Americans with AS. That’s pretty close to another inflammatory joint disease you may have heard of—rheumatoid arthritis (RA). RA affects 1.3 million people in the US.
Unlike other forms of arthritis, AS usually affects young adults; symptoms tend to start between 20 and 30 years of age.
Experts once thought AS affected more men than women by a ratio of 3:1. New research suggests it may be just as common in women as men.