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Sunlight exposure behaviour and vitamin D status in photosensitive patients: longitudinal comparative study with healthy individuals at U.K. latitude
Author(s) -
Rhodes L.E.,
Webb A.R.,
Berry J.L.,
Felton S.J.,
Marjanovic E.J.,
Wilkinson J.D.,
Vail A.,
Kift R.
Publication year - 2014
Publication title -
british journal of dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.304
H-Index - 179
eISSN - 1365-2133
pISSN - 0007-0963
DOI - 10.1111/bjd.13325
Subject(s) - sunlight , sun exposure , vitamin d and neurology , medicine , confidence interval , prospective cohort study , cohort , vitamin , cohort study , low latitude , zoology , latitude , physiology , biology , dermatology , physics , astronomy , geodesy , geography
Summary Background Low vitamin D status is prevalent in wintertime 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. Objectives To examine seasonal vitamin D status in photosensitive patients relative to healthy individuals and to assess quantitatively behavioural and demographic contributors. Methods This was a 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). Results Photosensitive patients achieved seasonal 25(OH)D variation, but insufficient (< 20 ng mL −1 ; 50 nmol L −1 ) and even deficient (< 10 ng mL −1 ; 25 nmol L −1 ) levels occurred at the summer peak in 47% and 9% of patients, respectively, rising to 73% and 32% at the winter trough. Adjusting for demographic factors, the mean values were lower than for healthy volunteers by 18% [95% confidence interval (CI) 4–29] in summer ( P = 0·02) and 25% (95% CI 7–39) in winter ( P = 0·01). Behavioural factors explained 25(OH)D differences between cohorts. Patients demonstrated lower weekend ultraviolet B 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: 2·94 μg per day). Supplementation and summer surface area exposure predicted summer peak and winter trough 25(OH)D levels. A 1 μg per day increment in supplementary vitamin D raised summer and winter 25(OH)D by 5% (95% CI 3–7) and 9% (95% CI 5–12), respectively (both P < 0·001). Conclusions 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.