Modifiable risk factors and the development of psoriatic arthritis in people with psoriasis

Background Psoriatic arthritis (PsA) is a progressive and often destructive joint disease affecting approximately 20% of people with psoriasis. Objectives To investigate associations between obesity, changes in body mass index (BMI), alcohol intake and smoking status and the development of PsA in people with psoriasis. Methods We undertook a cohort study involving incident cases of psoriasis identified from the U.K. Clinical Practice Research Datalink between 1998 and 2014. The associations between smoking, alcohol and BMI and development of PsA were assessed using generalized additive models. Additionally, the risks associated with a change in BMI during follow-up were investigated using distributed lag nonlinear models. Results We identified 90 189 incident cases of psoriasis (42% male, mean age 51 years), of whom 1409 had a subsequent record of PsA diagnosis. BMIs of 25 center dot 0-29 center dot 9, 30 center dot 0-34 center dot 9 and >= 35 center dot 0 kg m(-2) were significantly associated with an increased risk of developing PsA compared with BMIs < 25 center dot 0 kg m(-2): adjusted odds ratios (95% confidence intervals) 1 center dot 79 (1 center dot 46-2 center dot 19), 2 center dot 10 (1 center dot 67-2 center dot 63) and 2 center dot 68 (2 center dot 09-3 center dot 43), respectively. Reducing BMI over a 10-year period (linearly) was associated with a reduction in the risk of developing PsA compared with BMI remaining constant over the same period. Increased risks of developing PsA were associated with moderate drinking but not with former or heavy drinking or with current or past smoking status. Conclusions In this incident psoriasis cohort, increased BMI and moderate drinking, but not heavy drinking or smoking status, were associated with an increased risk of PsA in people with psoriasis. Importantly, we have shown that reducing weight may result in a reduction in the risk of developing PsA.