Zinc and atopic dermatitis: a systematic review and meta-analysis.

Zinc plays a central role in skin integrity via barrier and immune mechanisms and may also be relevant in the pathogenesis of atopic dermatitis (AD). However, little is known about the relationship between zinc and AD. We performed a systematic review to determine (i) the association between zinc levels or zinc deficiency and AD and (ii) the efficacy of oral zinc supplementation in the treatment of AD. We searched PubMed, Scopus, Web of Science and article references for observational studies on zinc levels or zinc deficiency in participants with AD vs. controls and for randomized control trials (RCTs) on zinc supplementation in AD. For observational studies, we calculated pooled standardized mean differences (SMDs) or odds ratios (ORs) along with 95% confidence intervals (CIs) using a random effects model. We included 14 observational studies and two RCTs. The pooled SMD demonstrated significantly lower serum (SMD 0.66, 95% CI 0.21-1.10, P = 0.004), hair (SMD 0.95, 95% CI 0.38-1.52, P = 0.001) and erythrocyte (SMD 0.95, 95% CI 0.38-1.52, P = 0.001) zinc levels in participants with AD compared to controls. Pooled unadjusted data from three studies showed a non-significant increased odds of AD in those with zinc deficiency compared with those without zinc deficiency (OR = 1.50, 95% CI 0.71-3.16, P = 0.28). One RCT of oral zinc supplementation among AD patients with zinc deficiency showed improvement in extent and severity of AD, while another RCT among all AD patients showed no significant improvement. All the studies were of low or moderate quality. We conclude that low serum, hair and erythrocyte zinc levels are associated with AD. However, the poor quality of included studies makes interpretation of these results problematic. High-quality observational studies are needed to confirm the association between low zinc levels and AD, and RCTs are required to evaluate the merit of zinc supplementation for the treatment or prevention of AD.