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By Elizabeth DeVita Raeburn, Contributing Writer, MedPage Today Reviewed by F. Perry Wilson, MD, MSCE; Instructor of Medicine, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse PlannerNote that this randomized trial failed to demonstrate an association between weight loss and improvement in psoriasis severity scores.Be aware that the trend towards statistical significance may reflect underpowering or the true lack of a weight loss:psoriasis link.Putting psoriasis patients on a low-calorie diet may improve quality of life and reduce psoriasis severity, researchers found.
The diet led to a reduction of 2.0 (95% CI 4.1-minus 0.1; P=.06) in the study's primary endpoint -- the Psoriasis Area and Severity Index (PASI) and a reduction of 2.0 (95% CI minus 3.6-minus 0.3, P =.02) in a secondary endpoint -- the Dermatology Life Quality Index (DLQI), Peter Jensen, MD, PhD, of Copenhagen University Hospital in Gentofte, Denmark, and colleagues reported online May 29 in JAMA Dermatology.
The authors of an accompanying editorial described the study as "encouraging," but also noted that the decrease in PASI was not statistically significant.
Michael Caglia, MD, and Gerald Krueger, MD, of University of Utah School of Medicine, wrote in an editorial that "a change of 3 PASI units was predicted to provide sufficient power to demonstrate an association of weight loss with decreased severity of psoriasis. This degree of significance (P=.06) indicates that the study was underpowered."
Epidemiological studies have long noted an association between psoriasis and obesity, but no prior randomized trials have examined the relationship between weight loss and psoriasis severity.
This 16-week, prospective, randomized trial included 60 people with a BMI between 27 and 40. Half the participants were randomly assigned to a low-energy diet consisting of 800 to 1,000 kcal per day for 8 weeks, followed by 8 weeks of a diet consisting of 1,200 kcal per day.
Mean weight loss was 15.4 kg (95% CI 12.3-18.5 kg; P<.001) greater in the intervention group than the control group. The median PASI for all patients at the beginning of the study was 5.4 (interquartile range, 3.8 to 7.6).
Most of the weight loss and the decrease in PASI occurred during the first 8 weeks of the study, suggesting a dose-response relationship between weight loss and PASI, wrote the authors.
"In fact, PASI leveled out from week eight, when participants increased their daily caloric intake," the authors wrote.
They noted an added benefit for study participants in the intervention group: a statistically significant reduction in insulin and plasma glucose levels compared with the controls.
There are several possible explanations for the improvement in psoriasis symptoms after weight loss. One hypothesis regarding the link between obesity and psoriasis is the low-grade systemic inflammation typical of both conditions. "Thus it is reasonable to assume that weight loss and subsequent reduction of obesity-derived pro-inflammatory mechanisms ... might improve the skin condition," the authors wrote.
Another explanation is that the medication used by some of the participants in the intervention arm of the study might have become more efficient as they lost weight and achieved a higher, more effective dose.
There were several limitations in the study. It was short, and long-term weight loss is generally maintained in only about 20% of people, the authors wrote. The primary investigator was unblinded and might have introduced observer bias. Most patients in the study also had only mild-to-moderate psoriasis, and the beneficial effects of weight loss might be more pronounced in patients with more severe disease, the authors wrote.
In addition, as part of the requirement for inclusion in the study, all participants who were on medication had to have maintained their use in the 3 months prior to the trial and during the 16-week study. The medication, wrote the authors, might have affected their ability to lose weight.
In their editorial Caglia and Krueger noted an additional limitation: the difficulty in enrolling patients in a study that involved a very restricted diet, which may have introduced selection bias. "A larger study population without entry bias and a longer duration is needed to validate their results," they wrote.
Still, the editorialists noted that the study was the first rigorous trial on the association between weight loss and psoriasis severity. The article and its authors, they wrote, "point the way to further research on the association between obesity and psoriasis, which many believe are inextricably linked."
The authors of the article, editorial, and practice gaps reported no conflicts of interest. The study was supported by Cambridge Manufacturing Company Limited, the Michaelson Foundation, the Aase and Ejnar Danielsen Foundation, the Research Foundation of the Danish Academy of Dermatology, the Danish Agriculture and Food Council, the Jacob Madsen and Olga Madsen Foundation, the Danish Psoriasis Research Foundation, and the Medical Research Foundation of the Capital Region of Denmark. The Parker Institute, where one of the authors, Robin Christensen, MSc, PhD, is employed, is supported by unrestricted grants from the Oak Foundation.
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