LE Rhodes, AR Webb, JL Berry, SJ Felton, EJ Marjanovic, JD Wilkinson, A Vail, R Kift
Sunlight Exposure Behaviour and Vitamin D Status in Photosensitive Patients: Longitudinal Comparative Study With Healthy Individuals at UK Latitude
Br J Dermatol 2014 Aug 11;[EPub Ahead of Print]
Low vitamin D status is prevalent in winter-time in populations at northerly latitudes. Photosensitive patients are advised to practise sun-avoidance, but their sunlight exposure levels, photoprotective measures and resulting vitamin D status are unknown.
Examine seasonal vitamin D status in photosensitive patients relative to healthy individuals and quantitatively assess behavioural and demographic contributors.
Longitudinal prospective cohort study (53.5°N) examining year-round 25-hydroxyvitamin D (25(OH)D) levels, sun-exposure behaviour and oral vitamin D intake in photosensitive patients diagnosed at a photoinvestigation unit (n=53) compared with concurrently-assessed healthy adults (n=109).
Photosensitive patients achieved seasonal 25(OH)D variation, but insufficient (<20ng/ml; 50nmol/l) and even deficient (<10ng/ml; 25nmol/l) levels occurred at summer-peak in 47% and 9% patients respectively, rising to 73% and 32% at winter-trough. Adjusting for demographic factors, mean values were lower than for healthy volunteers by 18% (95%CI 4 to 29%) in summer (P=0.02), 25% (7 to 39%) in winter (P=0.01). Behavioural factors explained 25(OH)D differences between cohorts. Patients demonstrated lower weekend UVB-doses (P<0.001), smaller skin surface-area exposure (P=0.004) and greater sunscreen use (P<0.001), while average oral vitamin D intake was low in both groups (photosensitive: 2.94μg/day). Supplementation and summer surface-area exposure predicted summer-peak and winter-trough 25(OH)D; 1μg/day increment in vitamin D supplement raised summer and winter 25(OH)D by 5% (95%CI 3 to 7%) and 9% (5 to 12%) respectively (both P<0.001).
Photosensitive patients are, through their photoprotective measures, at high risk of year-round low vitamin D status. Guidance on oral measures should target this patient group and their physicians.