Being overweight increases risk of psoriatic arthritis

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At a recent meeting of the Society for Investigative Dermatology (SID), researchers from Montreal presented a study which shows that patients with psoriasis face a greater risk of developing psoriatic arthritis if they are overweight.

Since 2002, Dr Kristina Duffin and colleagues at the University of Utah recruited more than a thousand psoriasis patients into the Utah Psoriasis Initiative (UPI). They have previously reported a higher prevalence of obesity among subjects with psoriasis compared with the general population. The mean Body Mass Index (BMI kg/m2) in this population is 29, compared with 26 in the general population, and 34% of study participants have a BMI of 30kg/m2 or more, compared with 18% in the general population.

At study entry, participants - who are on average 48 years old – were asked to recall the age at which their psoriasis began, together with an estimate of their weight at the age of 18. Analysis of the data shows that at the time of recruitment into the study, patients with psoriatic arthritis were heavier than those with psoriasis only (BMI 30.5 vs 27). Furthermore, BMI at aged 18 predicted the development of arthritis later. Among those with a BMI of less than 25 at 18 years, 26.5% went on to develop psoriatic arthritis; in those with a BMI of 25-30, 35.4% developed arthritis; and in those with a BMI of greater than 40, 40% went on to develop arthritis. In fact a one-unit increase in BMI increases the risk of psoriatic arthritis by 5.4%.

Comment:There are several points to be aware of in this report. Firstly, the study was published as an abstract and presented orally at a scientific meeting. It has yet to be published in a peer-reviewed scientific journal. This is important, because the results need to be scrutinized very carefully before we finally accept them as part of the established scientific literature. Another important point is to do with study design; participants were asked to recall their weight at aged 18 years. Most of us are rather bad at recalling such information which means that there is a real risk of “recall bias” in these results. Another observation which seems strange, is that they report the prevalence of obesity in the general population of 18%, which seems extraordinarily low (most developed countries have obesity prevalence rates of 25-30%).

Overall, however, these findings are potentially important. Not only are patients with psoriasis more likely to have weight problems, the heavier they are, the more likely they are to develop psoriatic arthritis. These data emphasis again the important of maintaining a health weight, especially if you have psoriasis. Put another way, if you have psoriasis and you are obese, the odds of avoiding psoriasis are stacked against you.

Reference:
Duffy KC; Abstract and oral presentation at Society for Investigative Dermatology Meeting (SID), Montreal, Canada 2009

Article prepared by:
Dr David Ashton MD PhD
11 May 2009