Serum folate levels and the risk of psoriasis: evidence from observational study and Mendelian randomisation

This study aimed to investigate the relationship between serum folate levels and the risk of psoriasis by integrating observational study with Mendelian Randomisation (MR) analysis. We firstly conducted an observational study using data from the National Health and Nutrition Examination Survey (NHANES). Subsequently, genetic instruments were selected for two-sample MR analyses to investigate the causal relationship between serum folate levels and the risk of psoriasis. The observational study showed no significant association between serum folate levels and psoriasis. In the fully adjusted model, neither serum folate level as a continuous variable (OR = 0·99, 95 % CI: 0·98, 1·00, P = 0·071) nor serum folate quartiles Q4 compared to Q1 (OR = 0·83, 95 % CI: 0·58, 1·19, P = 0·309) showed statistical significance. The MR analysis revealed that higher genetically predicted serum folate levels from Icelandic and Danish populations were significantly associated with a reduced risk of psoriasis (OR = 0·63, 95 % CI: 0·45, 0·88, P = 0·005). Similarly, higher genetically predicted serum folate levels from South Asian populations were significantly associated with a lower risk of psoriasis (OR = 0·84, 95 % CI: 0·72, 0·98, P = 0·025). Integrating observational study with MR analysis suggests that serum folate levels are protective factors against psoriasis, indicating that higher serum folate levels may help prevent the onset of the disease.