Obesity — both in childhood and adulthood — increases the risk of hip and knee osteoarthritis, but not hand osteoarthritis. That’s according to new research presented on June 15 at the Annual European Congress of Rheumatology in Amsterdam.

Though obesity and osteoarthritis are interconnected, it had been difficult to study their association, so researchers used a method called mendelian randomization, “which uses genetic variants to investigate whether a biomarker has an effect on the risk of developing disease,” according to a EULAR news release.

“Our results suggest the effect of adult body mass index seems to be stronger on knees, whilst childhood body mass index might impact both knee and hip osteoarthritis risk similarly,” said senior study author Daniel Prieto-Alhambra. “Interestingly our findings contradict previous studies that found an association between obesity and hand osteoarthritis.”

Prieto-Alhambra and colleagues found that every unit increase in body mass index increased the likelihood of self-reported osteoarthritis (2.7 percent increase), knee osteoarthritis (1.3 percent increase), and hip osteoarthritis (.4 percent increase). Childhood BMI increases, per unit, also yielded increased risk: 1.7 percent increase for osteoarthritis and .6 percent increases for knee osteoarthritis and hip osteoarthritis.

Although prior research had shown associations between BMI and hand osteoarthritis, this study did not find such an association in either adults or children.