The Gender Within Our Bones

Structure may explain some gender differences, too. A 2007 study at the University of Rhode Island examining 97 healthy men and women found that bone, cartilage thickness and volume were all greater in men than in women. 

“Women lose knee cartilage faster than men,” says Rakel.  Women lose cartilage from their tibia (the larger bone between the knee and ankle) at four times the rate of men, and they lose cartilage from the kneecap at three times the rate, according to a 2009 study at Monash University in Melbourne, Australia.

A 2007 study of sex and age on the change in cartilage volume in adults at the Menzier Research Institute in Hobart, Australia, found that greater cartilage loss in women than in men began at age 40 and increased with age. 

Conversely, a 2009 Osteoarthritis Initiative Study in the Annals of Rheumatic Diseases found that men had a slightly greater rate of cartilage loss.  But that study measured loss only over one year and in only one knee.

Fat’s Gender Signature

Obesity may also play a part in OA’s gender differences. “In our study, we found that women with knee osteoarthritis have an average body mass index (BMI) of  35 and men of 33, a significant difference,” says Rakel. A BMI — a measure of fat in relation to height — above 30 is considered obese.

A 2011 University of Michigan study of 1,066 participants found that obese women with high levels of leptin, a pro-inflammatory hormone involved in regulating appetite and fat storage, were more likely to have knee osteoarthritis than those with lower levels; the opposite was true for men.

Meanwhile, men, obese or not, who had higher levels of insulin resistance were more likely to have OA than men without.  Almost the opposite was true for women.

The difference may be a reflection of body composition, brain responsiveness, or [the effect of] different sex hormones, says epidemiologist Carrie Karvonen-Guiterrez, PhD, an assistant research scientist at the University of Michigan School of Public Health in Ann Arbor: “But both high leptin levels and insulin resistance [suggest] metabolic dysfunction.”