Distinguishing features of body mass index and psoriasis in men and women in Japan: A hospital-based case-control study.

Psoriasis is a chronic inflammatory disease and recent studies reported an association between obesity and psoriasis. To further investigate the association between body mass index (BMI) and psoriasis, a hospital-based retrospective case-control study was conducted in patients at the Department of Dermatology, Fukuoka University Hospital in 1998-2012. BMI values of psoriatic patients were compared with those of controls, who had skin diseases other than psoriasis. A total of 429 psoriatic patients (295 male, 134 female) and 16 028 controls were enrolled. The number of male patients with psoriasis sharply increased in their 30s, peaked in their 50s and remained relatively high through the 60s. The number of female patients showed a gradual increase to their 60s. Mean BMI was higher in psoriatic patients (23.96 ± 4.46) than in controls (22.22 ± 3.98, P < 0.0001). Age-stratified mean BMI in psoriatic patients was significantly higher at different ages in each sex. The odds ratio for psoriasis was significantly higher in obese patients. Stratified by age, there was a high odds ratio for psoriasis in men in their 40s, 70s and 80s, and in women in their 20s, 30s and 70s. The study suggests that, apart from those with a genetic predisposition, young women are less likely to develop psoriasis unless they have a high BMI, while men are more likely to acquire psoriasis if they have mild obesity in middle or older age. Our data may partially explain the higher male : female ratio (usually 2:1) in Japanese psoriatic patients.