High BMI increases the risk of several rheumatic diseases – but not equally for everyone


A new study from IGP shows that a higher body mass index (BMI) increases the risk of five different rheumatic diseases; rheumatism, osteoarthritis, gout, psoriatic arthritis and inflammatory spondylitis. The researchers were also able to see that BMI was a stronger risk factor for women compared to men when it came to the diseases gout and psoriatic arthritis. The study is presented in the scientific journal Arthritis and Rheumatology.

“The results from the study provide an increased understanding of the risks behind rheumatic disease and that a reduced body weight can be used as an intervention to reduce the risk of rheumatic disease, “says Weronica Ek who led the study.

Most rheumatic diseases are driven by inflammation in the body. They mainly affect joints, muscles and bones but important organs and vessels can also be affected. Symptoms of rheumatic disease can be fatigue, swelling and pain in the joints, stiffness and reduced movement function.

Previous studies have seen a link between rheumatic diseases and a high BMI (a kind of “corrected” body weight that also takes the individual's height into account). But it has not been fully investigated whether the link is due to high BMI actually increasing the risk of rheumatic disease and not simply because individuals with rheumatic disease have a higher BMI on average due to other, unknown reasons. This is a common problem in epidemiological studies based on observational data.

In the new study, the researchers have tried to circumvent the problem by instead making use of information in the human genes. By using specific genetic variants that can be linked to a high BMI, the researchers were able to show that men and women who have a genetic predisposition to a high BMI also have an increased risk of suffering from rheumatic disease.

“Although we have seen similar relationships before, it is difficult to identify actual relationships between BMI and disease. But when we found that the genes linked to high BMI were also associated with a higher risk of these rheumatic diseases, we could conclude that BMI really affects the risk of rheumatic disease,” says Weronica Ek.

The researchers used the same genetic method, called Mendelian randomization, to further study differences between men and women as well as possible differences in how BMI affects risk in women of childbearing age compared to when they have undergone menopause.

“For gout and for psoriatic arthritis, which is a common disease in patients with psoriasis, we saw that a high BMI was a stronger risk factor in women than in men. We also saw that the effect of BMI on the risk of developing osteoarthritis was lower in postmenopausal women compared to women of childbearing age, says Fatemeh Hadizadeh, postdoctoral researcher at IGP and one of the lead authors of the study.

The researchers also found that a certain increase in BMI did not result in a uniform increase in the risk of developing gout for individuals with low, normal and high BMI.

“We saw that an increase in BMI in normal-weight individuals resulted in a significantly greater relative increase in the risk of suffering from gout than an increase in BMI in already overweight and obese individuals. The risk therefore does not appear to increase as much for a person who is already overweight. However, the basic risk of suffering from gout is always higher, the higher your BMI. Such non-linear effects are interesting to study from a molecular biological perspective, to try to understand the underlying mechanisms behand why a higher body weight increases the risk of disease, says Torgny Karlsson, statistician at IGP and one of the main authors of the study.

Mer information:

The article in Arthritis & Rheumatology

Weronica Ek’ research in Åsa Johansson’s group

Last modified: 2022-01-26