Excess weight is a contributing factor for developing psoriasis, and the greater the body mass index (BMI), the higher the chance of getting the disease, according to a new study.

To investigate the causal relationship between BMI and psoriasis, the researchers used Mendelian randomization. They found that higher weight is a contributing factor to psoriasis and observed that greater BMI increased the chance of getting the disease. Their findings appear in PLOS Medicine.

"We calculated that the risk increased by nine percent for each higher whole number on the BMI scale," explains Mari Løset, MD, PhD, a dermatologist at St. Olavs Hospital and a postdoctoral fellow at the Norwegian University of Science and Technology's (NTNU) K.G. Jebsen Center for Genetic Epidemiology in a news release.

The observational study is a large collaboration among researchers from NTNU, England and North America. Some of the data being used is from the Health Survey in Nord-Trøndelag (HUNT) and the UK Biobank. Together, the analyses include data from 750 000 individuals.

But the researchers are still uncertain about just how higher weight can lead to psoriasis.

"We still don't know enough about the mechanisms behind this connection. Fatty tissue is an organ that produces hormones and inflammatory signalling molecules, which could be a contributing factor," says Løset.

So far, not much research has been done on whether weight loss can cause psoriasis to disappear, although a few clinical studies suggest the possibility.