Higher body mass index and moderate – but not heavy – drinking may increase the risk of individuals with psoriasis going on to develop psoriatic arthritis, a study has found.

Around one in five people with psoriasis will develop psoriatic arthritis (PsA), wrote Amelia Green of the University of Bath (England) and coauthors in the British Journal of Dermatology.

Previous studies have explored possible links between obesity, alcohol consumption, or smoking, and an increased risk of developing psoriatic arthritis. However, some of these studies found conflicting results or had limitations such as measuring only a single exposure.

In a cohort study, the Ms. Green and her colleagues examined data from the U.K. Clinical Practice Research Datalink for 90,189 individuals with psoriasis, 1,409 of whom were subsequently also diagnosed with psoriatic arthritis.

The analysis showed a significant association between increasing body mass index (BMI) and increasing odds of developing psoriatic arthritis. Compared with individuals with a BMI below 25 kg/m², those with a BMI of 25.0-29.9 had a 79% greater odds of psoriatic arthritis, those with a BMI of 30.0-34.9 had a 2.10-fold greater odds, and those with a BMI at or above 35 had a 2.68-fold greater odds of developing psoriatic arthritis (P for trend less than .001). Adjustment for potential confounders such as sex, age, duration and severity of psoriasis, diabetes, smoking, and alcohol use slightly attenuated the association, but it remained statistically significant.

Researchers also examined the cumulative effect of lower BMIs over time, and found that over a 10-year period, reductions in BMI were associated with reductions in the risk of developing PsA, compared with remaining at the same BMI over that time.

“Here we have shown for the first time that losing weight over time could reduce the risk of developing PsA in a population with documented psoriasis,” the authors wrote. “As the effect of obesity on the risk of developing PsA may in fact occur with some delay and change over time, our analysis took into account both updated BMI measurements over time and the possible nonlinear and cumulative effects of BMI, which have not previously been investigated.”

Commenting on the mechanisms underlying the association between obesity and the development of PsA, the authors noted that adipose tissue is a source of inflammatory mediators such as adipokines and proinflammatory cytokines, which could lead to the development of PsA. Increasing body weight also could cause microtraumas of the connective tissue between tendon and bone, which may act as an initiating pathogenic event for PsA.

Moderate drinkers – defined as 0.1–3.0 drinks per day – had 57% higher odds of developing PsA when compared with nondrinkers, but former drinkers or heavy drinkers did not have an increased risk.

The study also didn’t see any effect of either past or current smoking on the risk of PsA, although there was a nonsignificant interaction with obesity that hinted at increased odds.

“While we found no association between smoking status and the development of PsA in people with psoriasis, further analysis revealed that the effect of smoking on the risk of PsA was possibly mediated through the effect of BMI on PsA; in other words, the protective effect of smoking may be associated with lower BMI among smokers,” the authors wrote.

Patients who developed PsA were also more likely to be younger (mean age of 44.7 years vs. 48.5 years), have severe psoriasis, and have had the disease for a shorter duration.

The study was funded by the National Institute for Health Research, and the authors declared grants from the funder during the conduct of the study. No other conflicts of interest were declared.

SOURCE: Green A et al. Br J Dermatol. 2019 Jun 18. doi: 10.1111/bjd.18227

Obesity, moderate drinking linked to psoriatic arthritis