By David Liu, PHD

Saturday Sept 9, 2012 (foodconsumer.org) -- Obesity has been associated with an increased risk of psoriasis. But a new study in Annals of the Rheumatic Diseases suggests that it can also have an impact on the risk of psoriatic arthritis.

Psoriatic arthritis is a type of arthritis that often occurs in people with psoriasis of their skin, which is known.  The study led by Thorvardur Jon Love of Landspitali University Hospital, Fossvogur, Reykjavik, Iceland and colleagues confirmed that in a general population, overweight people were at  17 percent increased risk of psoriatic arthritis and people with obesity were 57 percent more likely to develop the disorder, compared to those who had a normal body mass index (less than 25 kg/m2).

The data used for the study came from The Health Improvement Network, a medical records database representative of the UK general population with data compiled for the period between1995 and 2010.  The first BMI measured after diagnosis of psoriasis was used and only incident cases of diagnosed psoriatic arthritis were counted for the study.  

Among 75,395 men and women with psoriasis at a mean age of 52 years, 976 developed psoriastic arthritis.  It was found that the incidence of psoriatic arthritis increased with increasing BMI.  Among psoriasis patients, those who were overweight were 9 percent more likely to develop psoriatic arthritis, compared to those who had a normal BMI.  Those who had obesity were 22 percent more likely to develop the disorder and those who were morbidly obese were 44 percent more likely to develop psoriatic arthritis.

In a study of a general population (about 2 million people), consisting of people with or without psoriasis, those who were overweight, had obesity or morbidly obesity were 17, 57 and 96 percent more likely to develop psoriatic arthritis, compared to those who had a normal body weight.

Overweight was defined as having a BMI of 25.0 to 29.9 kg/m2, obesity defined as having a BMI of 30.0 to 34.9 kg/m2 and morbidly obesity defined as having a BMI of 35 kg/m2 or greater.

The researchers concluded "This general population study suggests that obesity is associated with an increased risk of incident PsA (psoriatic arthritis) and supports the importance of weight reduction among psoriasis patients who often suffer from the metabolic syndrome and obesity.