High BMI could reduce men's risk of rheumatoid arthritis, but not women's

Scientists in Sweden analysed data from 383 patients, taken from two population based health surveys with a total of 50,705 participants, to discover that there is a strong association between a high BMI in men and a lower risk of developing rheumatoid arthritis (RA). However, this association was not found in women. The results were based on the Malmo Diet Cancer Study (MCDS) and Malmo Preventative Medicine Program (MPMP) data sets.

After the results had been adjusted for smoking, as that has been found to be negatively associated with obesity in men, men with a BMI over 25kg/m2 were estimated to be 63% less likely to develop RA in the MDCS, and 40 % less likely in the MPMP. When looking into why a high BMI would reduce the risk of men developing RA in the future, the scientists suggested that a high BMI more often reflects increased abdominal obesity or visceral fat in men compared with women, which could be protective against the development of RA. They have previously described a connection between high BMI and hormones, where metabolic pathways related to the adipose tissue and hormone-related factors could have a protective effect against RA.

Carl Turesson, lead author of the paper, commented that: "to our knowledge, this is the first nested case-control study to investigate this issue in men." He went on to comment on the effect for overweight and obese participants: "the effect of obesity on the risk of RA did not appear to be substantially different from that of overweight. However, a differential effect of very high BMI cannot be ruled out."