Adiposity and Physical Activity as Risk Factors for Developing Psoriatic Arthritis: Longitudinal Data From a Population-Based Study in Norway.

Objective: Adiposity is prevalent among patients with psoriatic arthritis (PsA). However, the temporal relation is unclear. The present study was undertaken to investigate whether adiposity and body fat distribution are related to the risk of developing PsA, and whether physical activity could modify the possible risk.

Methods: We included 36,626 women and men from the Norwegian Nord-Trøndelag Health Study without diagnosed PsA at baseline from 1995 to 1997. Cox regression analysis was used to estimate adjusted hazard ratios (HRs) with 95% confidence intervals (95% CIs) of incident PsA at follow-up from 2006 to 2008.

Results: During follow-up, 185 new cases of PsA were reported. Increases of 1 SD in body mass index (BMI) (4.2 and 3.5 kg/m for women and men, respectively) and waist circumference (10.8 and 8.6 cm, respectively) were associated with HRs of 1.40 (95% CI 1.24, 1.58) and 1.48 (95% CI 1.31, 1.68), respectively. Compared to individuals of normal weight, obese individuals had an HR of 2.46 (95% CI 1.65, 3.68), and overweight individuals had an HR of 1.41 (95% CI 1.00, 1.99). Comparing extreme quartiles of waist circumference yielded an HR of 2.63 (95% CI 1.73, 3.99). In analyses of combined effects using a BMI of <25 kg/m and high physical activity as reference, a BMI of ≥25 kg/m was associated with HRs of 2.06 (95% CI 1.18, 3.58) and 1.53 (95% CI 0.80, 2.91) among those with low and high physical activity levels, respectively. Corresponding HRs for high waist circumference and physical activity were 2.25 (95% CI 1.40, 1.63) and 1.85 (95% CI 0.95, 3.50).

Conclusion: The results suggest that adiposity, particularly central obesity, is associated with increased risk of incident PsA. Although there was no clear modifying effect of physical activity, high levels of physical activity reduced the risk of PsA, regardless of BMI.