Sir, A few studies conducted in adults have found a positive association between being overweight and risk of psoriasis, a serious disease affecting approximately 2% of the population. The relative risk was 1·5–2 for overweight and obese individuals.1, 2 The incidence of childhood psoriasis is unknown,3 but it has been reported that 10% of all cases occurred before the age of 10 years and 2% at < 2 years of age.4 If the association between overweight and psoriasis is present also in children, the increasing incidence of childhood obesity may be an emerging public health issue. In Italy the prevalence of overweight in preschool children was estimated to be 4·4%5 while in adolescents (aged 10–16 years) it was 14·9%.6 We have therefore conducted a case–control study between January and December 2005, at the Division of Pediatric Dermatology of San Paolo Hospital, Milan, Italy, which treats children under the age of 15 years. Cases were children with a first diagnosis of psoriasis made by a dermatologist. All eligible patients seen consecutively during the study period were invited to participate and all were included. We excluded children with eczema–psoriasis overlap and/or with a family history of both atopic dermatitis and psoriasis. All participants’ parents gave written informed consent. In accordance with the International Psoriasis Council,7 cases were classified as napkin psoriasis (n =4), psoriasis localized to the scalp (n =8), plaque psoriasis (n =68), guttate psoriasis (n =10) and nail psoriasis (n =6). Diagnoses in the control group included atopic dermatitis (n =53), angiomas and vascular malformations (n =6), viral diseases (n =11), bacterial diseases (n =3), fungal diseases (n =3), acne (n =3), naevi (n =5), pityriasis rosea (n =2), pityriasis alba (n =4), parasitic diseases (n =5) and alopecia areata (n =5). Thus 96 cases (52 boys and 44 girls) and 100 controls (43 boys and 57 girls) were included. Using a structured questionnaire, we collected information on height, weight, dietary habits of the child, family history of psoriasis (FHP), and smoking habits and alcohol consumption of the mother. We calculated a percentage measure of body mass index (BMI) as the actual weight of the child divided by the 50th centile weight at the age when the child’s height was on the 50th centile. Values over 110% were considered overweight, 90–110% normal weight, and below 90% underweight.8 Odds ratios (ORs), as estimators of the relative risk, and the corresponding 95% confidence intervals (CIs) were computed using unconditional multiple logistic regression with maximum likelihood fitting, in order to take into account the effect of age, sex and FHP. The mean ± SD age was 8·7 ± 2·9 years in cases and 7·3 ± 3·5 years in controls. FHP in first‐ or second‐degree relatives was reported by 55·2% of cases and 10% of controls. Table 1 gives the distribution of cases and controls according to BMI. A positive association between overweight and psoriasis was found (OR 2·55, 95% CI 1·31–4·96) when adjusted for sex and age. Similar results were evident after adjustment for sex, age and FHP (OR 3·38, 95% CI 1·56–7·30). The multivariate OR was 1·52 (95% CI 0·60–3·89) for underweight children. Association between body mass index (BMI) and psoriasis evaluated by odds ratio (OR) (95% confidence interval, CI) in overweight and underweight children compared with normal weight children (BMI expressed in percentiles). Italy, 2005 aSum does not add up to the total due to some missing values. bAdjusted for age (continuous) and sex. cAdjusted for age (continuous), sex and family history of psoriasis (yes/no). dReference category. Association between body mass index (BMI) and psoriasis evaluated by odds ratio (OR) (95% confidence interval, CI) in overweight and underweight children compared with normal weight children (BMI expressed in percentiles). Italy, 2005 aSum does not add up to the total due to some missing values. bAdjusted for age (continuous) and sex. cAdjusted for age (continuous), sex and family history of psoriasis (yes/no). dReference category. Table 2 considers the association between measures of body weight and psoriasis in strata of sex and age. None of the stratification variables showed a significant interaction with BMI. Significant positive associations were found for overweight in boys (OR 4·63, 95% CI 1·40–15·28) and younger children (age ≤ 10 years) (OR 3·19, 95% CI 1·40–7·28). Association between body mass index (BMI) and psoriasis evaluated by odds ratio (OR)a (95% confidence interval, CI) in overweight and underweight children compared with normal weight children in categories of sex and age (BMI expressed in percentiles). Italy, 2005 aAdjusted for family history of psoriasis (yes/no) and age (continuous) or sex, when appropriate. bca : co, number of cases vs. number of controls. cReference category. Association between body mass index (BMI) and psoriasis evaluated by odds ratio (OR)a (95% confidence interval, CI) in overweight and underweight children compared with normal weight children in categories of sex and age (BMI expressed in percentiles). Italy, 2005 aAdjusted for family history of psoriasis (yes/no) and age (continuous) or sex, when appropriate. bca : co, number of cases vs. number of controls. cReference category. Some limitations of this study should be considered. Cases were recruited regardless of disease severity and more severe cases may be more easily diagnosed. The number of cases was limited by the rarity of the disease, and this limits the possible inference in subgroups. Among strengths of this study are the validity of the diagnosis of cases and controls, made by the same dermatologists, the complete participation rate, and the uniform data collection, which ensures comparability of information collected in cases and controls. Herron et al.,9 studying a case series of adult patients enrolled in the prospective Utah Psoriasis Initiative, collected information about body image at 18 years of age, at the onset of psoriasis, and at enrolment. Based on these data, no association was observed between obesity in early life and psoriasis, because body weight did not increase until after the onset of psoriasis, but it changed to overweight after the diagnosis. In our study, however, there was a greater prevalence of overweight in cases, measured at diagnosis of psoriasis, than in controls. In conclusion, the results of the present study indicate that being overweight is an important risk factor for the onset of psoriasis in children. Childhood overweight has been associated with a variety of adverse consequences such as cardiovascular diseases, type 2 diabetes and sleep apnoea. Psoriasis should therefore be added to the adverse consequences of childhood obesity.10 Conflicts of interest: none declared.
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Boccardi et al. (2009) studied this question.