Risk of Psoriasis Lowered with Gastric Bypass?

A new study published this December in JAMA Surgery has found some interesting connections between gastric bypass surgery and the onset and severity of psoriasis.  Researchers in Denmark analyzed over 13,000 individuals who underwent gastric bypass and gastric banding procedures between 1997 and 2012, and determined the risk these individuals had of developing new-onset psoriasis, new-onset psoriatic arthritis, or the development of severe psoriasis from a previously more moderate form.

Psoriasis has long been studied in conjunction with obesity, weight-loss, and different diets.  The lead author of the study, Dr. Alexander Egeberg, of the Herlev and Gentofte Hospital in Hellerup, Denmark notes, “In recent years, emerging data has significantly associated psoriasis with obesity, in a disease-severity dependent manner. Moreover, low-energy diets and subsequent weight loss have been reported to improve the prognosis of psoriasis.”

What does the research tell us?

Gastric bypass, as opposed to gastric banding, has an effect on the appetite-reducing hormone, GLP-1 (glucagon-like peptide 1).  This hormone lowers glucose in the blood, however, it has also been hypothesized to have anti-inflammatory properties as well.  Data on over 12,000 individuals who underwent gastric bypass and over 1,000 who underwent gastric banding were compared pre- and post-surgery, to determine the change in risk of psoriasis development and severity.  Of these individuals, 75% were women, and the mean age at time of procedure was roughly 40 years old.

Instead of using a control group of the general population, the researchers decided to compare the individuals to themselves before and after treatment, in order to assess individual changes in risk.  After adjusting for confounding variables, the researchers found that the ratio of developing new-onset psoriasis was 0.52 for the bypass group, and 1.23 for the banding group.  A similar trend was seen in both the progression to severe psoriasis for those with previously-existing psoriasis, as well as the development of psoriatic arthritis.  For all three measures, there was a significant decrease in risk after bypass surgery, as opposed to banding.  The amount of follow-up time (in person-years) before and after surgery was also greatly reduced in the bypass group, as opposed to a very small decrease in the banding group (160,000 to 33,000, and 10,000 to 7,000, respectively).

What does it mean?

The authors conclude, "We observed a reduced risk and improved prognosis of psoriasis following gastric bypass surgery, whereas no difference was observed for gastric banding. Although differences in post-surgical weight loss may partly explain this observation, our findings could also support the hypothesis of a role for GLP-1. Gastric bypass surgery results in a 20-fold increase in GLP-1, whereas gastric banding does not, likely due to re-routing of ingested nutrients in gastric bypass surgery."  Previously, gastric bypass has been known to decrease the incidence of obesity-related conditions post-procedure, such as diabetes.  However, new information, like the data from this study, could indicate that the procedure may have the ability to decrease the risk or severity of immune-related conditions as well.

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