The statistically significant association between psoriasis and both obesity and type 2 diabetes comes down to genetics, according to a large population-based study of twins.
Across the entire cohort of 33,588 Danish twins, researchers found the prevalence of psoriasis was 53% higher in individuals with type 2 diabetes, while the prevalence of psoriasis was 81% higher in individuals with a body mass index of at least 35, after adjustment for confounders such as sex, age, and smoking (JAMA Dermatol. 2016 April 27. doi:10.1001/jamadermatol.2015.6262).
Among the 449 twin pairs discordant for psoriasis, the risk for obesity was more than double in the twin with psoriasis compared to the unaffected twin, although this was significant only among dizygotic pairs, not monozygotic pairs.
The twin analysis also found that the risk of type 2 diabetes was the same between twins with and without psoriasis.
“Increased plasma levels of tumor necrosis factor, tumor necrosis factor receptors, and interleukin 6, which have important roles in the pathogenesis of psoriasis, have been found to be linked with obesity,” wrote Dr. Ann Sophie Lønnberg of the department of dermato-allergology, Gentofte Hospital, University of Copenhagen, and her associates.
“The association between type 2 diabetes mellitus and psoriasis also might be owing to increased tumor necrosis factor production from psoriatic inflammation and low-grade obesity inflammation, because it contributes to insulin resistance,” they wrote.
While obesity and type 2 diabetes are known comorbidities of psoriasis, Dr. Lønnberg and colleagues said this was the first study, to their knowledge, to explore the contribution of genetic and environmental factors to this interaction, and they suggested that future studies could look for genes and epigenetic factors that might underlie these associations.
Their analysis showed the genetic correlation between psoriasis and type 2 diabetes was 0.13, while the environmental correlation was 0.10. Similarly, the genetic correlation between psoriasis and BMI was 0.12, while environmental correlation was –0.05.
No conflicts of interest were declared.