Increased risk of RA seen in women who are overweight, but not in men

Being overweight or obese, and having abdominal obesity and a higher body fat percentage may all be associated with an increased risk of developing rheumatoid arthritis (RA) in women, but not in men, according to results from a population study conducted by Danish researchers at the Annual European Congress of Rheumatology (EULAR 2017).

Researchers included 52,824 subjects (age range: 50 to 64 years; 52% female), between 1993 and 1997. At enrollment, researchers collected information including body fat composition measurements and lifestyle factors. They followed subjects for a median of 21 years until they developed RA, died, or were lost to follow-up, or October 2016, whichever came first.

They used The Danish National Patient Registry to determine which subjects developed RA, after adjusting hazard ratios for age, smoking status, total tobacco use (g/day), smoking duration, alcohol consumption, socioeconomic status, physical activity, and total intake of n-3 fatty acids.

In total, 283 women and 100 men developed RA, with a median time to onset of 7 years.

In women, the HR for a BMI of 25 to 29.99 kg/m² (overweight) was 1.48 (95% CI: 1.14-1.91), and for a BMI of > 30 kg/m² (obese), 1.54 (95% CI: 1.09-2.17).

In men, the HR for a BMI of 25-29.99 kg/m² was 0.83 (95% CI: 0.55-1.24) and for a BMI > 30 kg/m², 0.69 (95% CI: 0.37-1.30).

Abdominal obesity was defined as a waist circumference of greater than 88 cm in women, and greater than 102 cm in men. For women with abdominal obesity, the HR was 1.24 (0.96-1.611), and for each 1% higher body fat percentage, 1.03 (95% CI: 1.01-1.05). In men with abdominal obesity, the HR was 1.16 (95% CI: 0.75-1.80), and for each 1% higher body fat percentage, 0.99 (95% CI: 0.96-1.03).

Researchers sought to further define the relationship between body fat percentage and the risk of developing RA with a restricted cubic spline statistical analysis. They found a positive slope in women, confirming this direct relationship, but observed no such linear association in men.

“One possible explanation for these inconsistencies is that while BMI has been the preferred surrogate measure for being overweight in these studies, BMI only correlates modestly with total amount of body fat and does not accurately reflect fat distribution,” said lead author Dr. Asta Linauskas, University Hospital, Aarhus, Denmark.

“Our results support an association between the risk of developing RA and three different criteria for being overweight or obese in women. We believe RA should be included in the list of all the other medical conditions linked to obesity. It would certainly make sense for women with a family history of RA to try to avoid becoming overweight,” she concluded.