In a new study suggesting associations between psoriasis and type 2 diabetes, BMI, and obesity, researchers investigated potential contributing factors to this association.
“Psoriasis has been associated with components of the metabolic syndrome, particularly obesity and type 2 diabetes mellitus,” researchers wrote in JAMA Dermatology.
“Several factors might explain the association between psoriasis and the metabolic syndrome, notably genetics, environmental exposures, such as tobacco smoking, alcohol consumption, psychological stress, and physical activity, and shared immunoinflammatory pathways. These various factors may act in concert to explain the co-occurrence of psoriasis and the metabolic syndrome,” they added.
To further explore this association, the researchers conducted a cross-sectional, population-based study of 34 781 Danish twins aged 20 to 71 years. Data from a questionnaire on psoriasis were validated against hospital discharge diagnoses of type 2 diabetes and self-reported BMI.
Of the 33 588 twins for whom complete data were available, more than half were women. Prevalence of psoriasis in the total twin sample was 4.2% (630 men; 771 women), and prevalence of diabetes was 1.4% (224 men; 235 women), according to the study results. Average BMI for the group was 24.5; 6.3% of the population were obese with BMIs ranging from 30 to 34 and 1.7% had BMIs of 35 or greater.
The prevalence of psoriasis was 7.6% (n=31) among the 459 people with diabetes vs 4.1% (n=1370) among those without diabetes, the researchers reported. After multivariable adjustment, they observed a significant association between psoriasis and type 2 diabetes (odds ratio [OR]=1.53; P=.04).
Data showed that the average BMI of those with psoriasis was higher than among those without the condition (25 vs 24.4), with the risk for obesity being higher among those with psoriasis. The prevalence of obesity also increased with increasing BMI, and similar to diabetes, results revealed a significant association between psoriasis and increasing BMI (OR=1.81; P=.001 for those with a BMI greater than 35) after multivariable adjustment.
The researchers identified 720 twin pairs discordant for psoriasis, where 1 twin had the disease while the other did not. Twins with psoriasis had a higher BMI compared with co-twins without the condition and were also more likely to be obese.
When evaluating the psoriasis-discordant pairs, results indicated that the association between psoriasis and obesity was diluted in monozygotic twins (OR=1.43; P=.50) as compared with dizygotic twins (OR=2.13; P=.04).
Variance decomposition suggested that additive genetic factors accounted for 68% of the variance in the susceptibility to psoriasis; for 73% of the variance in susceptibility to type 2 diabetes; and for 74% of the variance in BMI. The data demonstrated genetic correlations of 0.13 (P=.17) between psoriasis and type 2 diabetes and 0.12 (P<.001) between psoriasis and BMI.
In terms of environmental factors, the correlation between psoriasis and type 2 diabetes was 0.1 (P=.63) and -0.05 (P=.44) between psoriasis and BMI.
Psoriasis may predispose individuals to more sedentary lifestyles that may predispose them to obesity and diabetes, or diabetes and obesity could lead to psoriasis, the researchers explained, noting that they could not infer causation.
“Psoriasis, type 2 diabetes mellitus, and obesity are strongly associated in adults after taking key confounding factors such as sex, age, and smoking into account,” they concluded. “Conducting future studies on specific genes and epigenetic factors that cause this association is relevant.”
In an accompanying editorial, Joel M. Gelfland, MD, MSCE, of the University of Pennsylvania Perelman School of Medicine in Philadelphia, explained that the association between psoriasis and obesity and type 2 diabetes has been well established in other studies, but commented that this study adds a new dimension to previous findings.
“The unique twin design of the study by Lønnberg and colleagues, in which increasing BMI was associated with a diagnosis of psoriasis, allowed the investigators to identify a genetic correlation between psoriasis and BMI,” Dr Gelfland wrote.
In light of these results as well as other evidence linking psoriasis with cardiometabolic diseases, dermatologists may be well placed to screen for these conditions or offer some lifestyle counseling, he noted.
“Despite these compelling reasons to identify diabetes in patients with psoriasis, a major practice gap remains in dermatologists’ screening and counseling of patients for cardiovascular risk factors. The weight of evidence linking psoriasis to cardiometabolic disease continues to increase, tipping the scale toward changing clinical practice in dermatology,” Dr Gelfland concluded.
- Lønnberg AS, Skov L, Skytthe A, Kyvik KO, Pedersen OB, Thomsen SF. Association of Psoriasis With the Risk for Type 2 Diabetes Mellitus and Obesity. JAMA Dermatol. 2016. doi:10.1001/jamadermatol.2015.6262.
- Gelfland JM. Psoriasis, Type 2 Diabetes Mellitus, and Obesity: Weighing the Evidence. JAMA Dermatol. 2016. doi:10.1001/jamadermatol.2016.0670.