If you’re a woman headed into middle age, keep your weight down to protect your joints. Otherwise, get ready for knee pain. Research shows that about two of three women age 50 and older suffer knee problems. The annual cost of this osteoarthritis (OA) is up to about $13 billion in lost productivity in the U.S. In addition, American doctors yearly perform about 500,000 total knee replacements that cost another $14 billion.

“Our study is the first community-based investigation of knee pain patterns using multiple assessment points over a 12-year period,” explains lead author Nigel Arden at the University of Oxford in the U.K. “Understanding the prevalence and predictors of knee pain is the first step in developing comprehensive pain assessment plans that could lead to more targeted treatment options for those burdened by OA.”

The scientists note that being overweight significantly increases stress on the knees and increases your chances of knee problems.