Prevalence and predictors of low vitamin D status in patients referred to a tertiary photodiagnostic service: a retrospective study.

BACKGROUND/
PURPOSE: Low vitamin D levels have been associated with adverse effects on health. The primary source of vitamin D is cutaneous production during sunlight exposure. Sun avoidance can restrict vitamin D photosynthesis and is common practice amongst patients with photosensitivity. Few studies have examined vitamin D status in this population, particularly those in northern latitudes. The purpose of this study was therefore to investigate the prevalence and possible predictors of low vitamin D status in patients referred to a tertiary photodiagnostic service.
METHODS: A case note review of 165 patients who attended the National Photodiagnostic Service for assessment at the Photobiology Unit in Dundee, Scotland (latitude 56 °N) over 1 year was conducted. Clinical information and serum 25-hydroxyvitamin D (25(OH)D) concentration were documented. Multivariate analyses were used to identify predictors of vitamin D status.
RESULTS: Mean 25(OH)D concentration was 41.9 nmol/L [standard deviation (SD) 22.0]. Forty percent of patients had insufficient vitamin D levels [25(OH)D 25-49 nmol/L] and 25% were vitamin D deficient [25(OH)D<25 nmol/L]. Blood collection in winter was the strongest predictor of low 25(OH)D status (P<0.001); strict photoprotection (P=0.04), onset of symptoms within an hour of sunlight exposure (P=0.01) and abnormal monochromator phototesting responses (P=0.009) also predicted low vitamin D levels. Supplement use was associated with higher vitamin D levels (P<0.001), even amongst patients who strictly avoided sunlight (P=0.03).
CONCLUSIONS: Patients with photosensitivity who live in northern latitudes are at high risk of low vitamin D levels, particularly in winter and spring. Increased awareness of this risk is crucial to ensure preventative strategies, such as supplementation, are implemented.