Studies have link psoriasis and higher weight, but the causal relationship between the two has been unclear. What triggers what? Higher BMI may contribute to increase inflammation of the skin, which can exacerbate psoriasis, but it could also be that psoriasis leads to a person being less physically active and thus gaining weight, explains Mari Loset.
They is a medical doctor at the Department of Dermatology 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. Loset is part of a team that been involve in a study of the causal relationship between BMI and psoriasis.
Inflammatory condition of the skin
BMI stands for body mass index and is a measure of body fat content. It is calculate from a person’s height and weight. The observational study is a large collaboration among researchers from NTNU, England and North America. Some of the data being use are from the Health Survey in Nord-Trondelag (HUNT) and the UK Biobank. Together, the analyses include data from 750 000 individuals.
Psoriasis is a chronic inflammatory condition of the skin; which causes a red, scaly rash. The cause of the disorder is probably multifactorial, involving both heredity and the environment. Worldwide, two to four per cent of the population is affect by psoriasis. The incidence is particularly high in Norway.
Hence similar studies from other parts of the world substantiate the fact that the condition is increasing, says the postdoctoral fellow. To investigate the causal relationship between BMI and psoriasis, the researchers use a method called Mendelian randomization. It is name after Gregor Mendel, who is known as the father of genetics.
According to Mendel’s principles of inheritance, whether they inherit a certain variant of genes; hence from our mother or our father is random. Genetic variants are randomly distributed, or randomize, between individuals. Mendelian randomization means that nature itself distributes individuals randomly into groups base on genes. This way, they can avoid the results being influence by external factors,” says Loset.
Genes are relate to disease
Our understanding of how genes are relate to disease is increasing at record speed; so in this study they use known genetic variants as markers for BMI and psoriasis,” she adds. By using Mendelian randomization; hence the researchers find that higher weight is a contributing factor to psoriasis. They observe that greater BMI increase the chance of getting the disease.
They calculate that the risk increase by nine percent for each higher whole number on the BMI scale,” Loset says. But the researchers are still uncertain about just how higher weight can lead to psoriasis. They 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 Loset.
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. 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,” says Mari Loset.