Psoriasis is understood to have a link with obesity, but a causal relationship between body mass and psoriasis has not been established. Some have suggested that obesity could promote skin inflammation, although it may also be the case that skin disorders may lead to reduced physical activity and contribute to higher weight.
A recent study
used Mendelian randomization, which uses genetic variants to randomly allocate individuals to groups based on genotype, to further investigate the causal relationship between body mass index (BMI) and psoriasis. It found that as BMI rises, so too does the risk for developing psoriasis.
The researchers used data for 396,495 participants whose individual-level data were contained in UK and Norwegian databases and 356,926 participants who had summary-level data available. Genotyping of participants was performed using 1 of several arrays, and logistic regression models were used to estimate the observational association between BMI and psoriasis. These analyses were adjusted for age, sex, smoking status, alcohol intake, and educational level.
The Mendelian randomization showed that a 1 kg/m2
increase in BMI was associated with an 8% increase in the risk of psoriasis. Similar causal estimates were found even when stratifying cases of psoriasis by patients’ self-reports and those defined by data extraction efforts.
While the study was limited by factors such as patient reporting of psoriasis and the fact that the participants studied were only of European ancestry, the findings do suggest that approaches to preventing and treating psoriasis may benefit from targeting adiposity levels in addition to immune pathways in the skin.
“We still don't know enough about the mechanisms behind this connection,” said Mari Løset, MD, one of the study’s authors, in a statement about her team’s findings. “Fatty tissue is an organ that produces hormones and inflammatory signaling molecules, which could be a contributing factor.”
Løset added that “Psoriasis is a very complex disease and we hope to study subgroups, especially individuals with severe psoriasis. The hypothesis is that we will be able to observe even greater links with higher weight.”
Budu-Aggrey A, Brumpton B, Tyrrell J, et al. Evidence of a causal relationship between body mass index and psoriasis: a Mendelian randomization study [published online January 31, 2019]. PLoS Med.