Background. Psoriasis is a multifactorial disease affected by both genetic and environmental factors. Several comorbid conditions, such as smoking, depression and obesity have been found to be associated with psoriasis. This study addressed the association of psoriasis and obesity using same-gender full siblings as controls, correlating between body mass index (BMI) and severity of psoriasis as determined by body surface area (BSA) and the Physician's Global Assessment (PGA). Methods. In total, 88 patients undergoing outpatient treatment for psoriasis were surveyed for demographic information, psoriasis history, social history, personal and family medical history, whether they had a same-gender full sibling and if so, the age, weight and height of the sibling. Height, weight, PGA scores and percentage of BSA affected by psoriasis, were recorded for each patient. BMI was calculated for each patient and their same-gender full sibling. Results. A positive association between psoriasis severity and BMI was found. PGA score increased with BMI (Spearman's correlation, rs = 0.29, P = 0.007). There was also a positive correlation between BMI and BSA%, rs = 0.24, P = 0.02. A significant difference in BMI between patients with psoriasis and the same-gender full sibling control was seen for women (mean ± SD 30.2 ± 10.2 vs. 27.6 ± 7.3 kg/m2, respectively, P = 0.02), but not for men. Conclusion. In this study, psoriasis severity was found to be related to the level of obesity. Using same-gender siblings as genetic controls for predisposition to both obesity and psoriasis, patients with psoriasis were more likely to have a higher BMI, particularly for women. This study reinforces the need to treat the whole patient and to encourage healthy living, such as maintaining an appropriate weight, proper eating habits and exercise. Limitations of this study include the relatively small number of patients enrolled, potential inaccuracies in sibling BMIs calculated from information provided by patients, and a lack of information about dietary habits, exercise and lifestyle.
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