BackgroundVitamin D has been reported to be associated with many allergic diseases. There are a limited number of the studies of vitamin D supplementation in patients with chronic spontaneous urticaria (CSU). This study aims to study the relationship between vitamin D and CSU in terms of serum vitamin D levels, and the outcomes of vitamin D supplementation.MethodsA literature search of electronic databases for all relevant articles published between 1966 and 2018 was performed. The systematic literature review was done following Preferred Reporting Items for Systematic Reviews and Meta-analysis recommendations.ResultsSeventeen eligible studies were included. Fourteen (1321 CSU cases and 6100 controls) were concerned with serum vitamin D levels in CSU patients. Twelve studies showed statistically significant lower serum vitamin D levels in CSU patients than the controls. Vitamin D deficiency was reported more commonly for CSU patients (34.3–89.7%) than controls (0.0–68.9%) in 6 studies. Seven studies concerned with vitamin D supplementation in CSU patients showed disease improvement after high-dosages of vitamin D supplementation.ConclusionCSU patients had significantly lower serum vitamin D levels than the controls in most studies. However, the results did not prove causation, and the mechanisms were not clearly explained. Despite the scarcity of available studies, this systematic review showed that a high dosage of vitamin D supplementation for 4–12 weeks might help to decrease the disease activity in some CSU patients. Well-designed randomized placebo-controlled studies are needed to determine the cut-off levels of vitamin D for supplementation and treatment outcomes.

Hair pigmentation is regulated by follicular melanogenesis, in which the process consists of melanin formation and transfer to keratinocytes in the hair shaft. Human hair follicles contain two types of melanin: the brown‐black eumelanin and yellow‐red pheomelanin. Eumelanin is commonly present in black and brown hair while pheomelanin is found in auburn and blonde hair. Hair follicle melanogenesis is under cyclical control and is concurrently coupled to hair growth. Many factors including intrinsic and extrinsic factors affect the follicular melanogenesis. Though many studies have been conducted to identify the pathogenesis and regulation of hair pigmentation, the etiology of canities and hair pigmentation is still unclear. The pathogenesis of canities or gray hair is believed to occur either from insufficient melanin formation due to melanocyte degeneration or a defect in melanosomal transfer. Canities is an aging sign which often interferes with one's socio‐cultural adjustment. On the other hand, premature canities correlate with diseases such as osteopenia and cardiovascular disease. Risk factors associated with canities are not only genetic but also external causes. For example, smoking, alcohol consumption, and stress are among the most common factors. Camouflage techniques are still used as the primary treatment of canities. Further treatments for canities are being developed to achieve the true reversal of hair pigmentation.

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