Background
It is increasingly clear that triglyceride-rich lipoproteins are proinflammatory and cause low-grade systemic inflammation. However, it is currently unknown whether elevated plasma triglycerides are causally related to the development of psoriasis, a skin disorder driven by chronic inflammation.

Objectives
To determine if elevated plasma triglycerides are associated with increased risk of psoriasis in observational and Mendelian randomization analysis.

Methods
Consecutive individuals from the Copenhagen General Population Study were included. We used plasma triglycerides (n = 108 043) and a weighted triglyceride allele score (n = 92 579) on nine known triglyceride-altering genetic variants. Genetic results were replicated in 337 159 individuals from the UK Biobank. Psoriasis was defined using the International Classification of Diseases, version 10 (ICD-10) code for hospital contact in the main analyses, and prescription of topical antipsoriatics for mild psoriasis in the sensitivity analysis.

Results
During a follow-up of median (range) 9.3 (0.1–15.1) years from 2003 to 2015 through 2018, 855 (1%) individuals were diagnosed with psoriasis by ICD-10 in the observational analysis and 772 (1%) in the Mendelian randomization analysis. In the observational analysis, the multivariable adjusted hazard ratio for psoriasis by ICD-10 was 1.26 [95% confidence interval (CI) 1.15–1.39] per doubling in plasma triglycerides with a corresponding causal odds ratio of incident psoriasis of 2.10 (95% CI 1.30–3.38). Causality was confirmed from data from the UK Biobank. Results were similar but slightly attenuated when we used topical antipsoriatic prescriptions for mild psoriasis.

Conclusions
Elevated plasma triglycerides are associated with an increased risk of psoriasis in observational and Mendelian randomization analysis.