Background Obesity is associated with an increased risk of psoriasis; however, its potential impact on the risk of psoriatic arthritis (PsA) remains unclear.

Objectives To evaluate the association between body mass index (BMI) and the risk of PsA among patients with psoriasis from the general population.

Methods The authors conducted a cohort study using data from The Health Improvement Network, an electronic medical records database representative of the UK general population, collected between 1995 and 2010. The exposure of interest was the first BMI measured after psoriasis diagnosis and endpoints were incident cases of physician-diagnosed PsA. The authors estimated the RR of PsA after adjusting for age, sex, and histories of trauma, smoking and alcohol consumption.

Results Among 75 395 individuals with psoriasis (43% male, mean follow-up of 5 years, and mean age of 52 years), 976 developed PsA (incidence rate, 26.5 per 10 000 person-years). The PsA incidence rates increased with increasing BMI. Compared with psoriasis patients with BMI <25 kg/m², the RRs for developing PsA were 1.09 (0.93–1.28) for BMIs from 25.0 to 29.9, 1.22 (1.02–1.47) for BMIs from 30.0 to 34.9 and 1.48 (1.20–1.81) for BMIs ≥35.0. In our secondary analysis among all individuals, regardless of psoriasis (∼2 million), the corresponding multivariate RRs tended to be stronger (1.0, 1.17, 1.57, 1.96; p for trend <0.001).

Conclusions This general population study suggests that obesity is associated with an increased risk of incident PsA and supports the importance of weight reduction among psoriasis patients who often suffer from the metabolic syndrome and obesity.