The relevance of serum vitamin D in psoriasis: a review

Observational research has identified low serum levels of 25-hydroxyvitamin D (25[OH]D) in many non-skeletal diseases. Whether this is causal or due to underlying illness is unknown. Low serum 25[OH]D levels are also reported in the general population. Observational and experimental studies identify that vitamin D supplementation may be beneficial in reducing all-cause mortality in elderly women, as well as cancer mortality. Our aim was to review the literature to identify the relevance of serum 25[OH]D levels in psoriasis. Forty-five studies were included in our analysis. Most of these studies identified low serum 25[OH]D levels in psoriasis patients. Evidence of causality is lacking. Treatment with phototherapy leads to an increase in serum 25[OH]D. There is little evidence that the increase in 25[OH]D after phototherapy correlates with improved disease severity. Multiple studies report an improvement in psoriasis with vitamin D supplementation. These data are predominantly from small observational or non-randomised interventional studies. Randomised controlled trials to date have had small numbers and short follow-up periods. The optimal dose of supplementation is unknown and dosing is not standardised across different studies. The definition of vitamin D insufficiency varies across studies. Low serum 25[OH]D levels may be associated with comorbidities in psoriasis patients, including metabolic syndrome and cardiovascular risk. Evidence of causation is absent. Until further high-quality evidence is available, the relevance of low serum 25[OH]D levels in psoriasis patients is unknown, as is the benefit of supplementation on disease control. Supplementation in patients with low 25[OH]D is of benefit to those at risk of impaired bone health.