title: Sunlight exposure behaviour and vitamin D status in photosensitive patients: longitudinal comparative study with healthy individuals at U.K. latitude.
abstract: 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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Dermatology Centre, Institute of Inflammation and Repair, University of Manchester, Manchester Academic Health Science Centre, Salford Royal NHS Foundation Trust, Manchester, U.K.
authors.forename: L E
authors.initials: LE
authors.lastname: Rhodes
authors.forename: A R
authors.initials: AR
authors.lastname: Webb
authors.forename: J L
authors.initials: JL
authors.lastname: Berry
authors.forename: S J
authors.initials: SJ
authors.lastname: Felton
authors.forename: E J
authors.initials: EJ
authors.lastname: Marjanovic
authors.forename: J D
authors.initials: JD
authors.lastname: Wilkinson
authors.forename: A
authors.initials: A
authors.lastname: Vail
authors.forename: R
authors.initials: R
authors.lastname: Kift
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D019587:Dietary Supplements; D004781:Environmental Exposure / Q000009:adverse effects / Q000032:analysis / Q000517:prevention & control; D005260:Female; D015438:Health Behavior; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000378:metabolism; D010787:Photosensitivity Disorders / Q000097:blood* / Q000150:complications / Q000517:prevention & control; D011446:Prospective Studies; D012621:Seasons; D013472:Sunlight / Q000009:adverse effects*; D013473:Sunscreening Agents / Q000627:therapeutic use; D014807:Vitamin D / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000097:blood / Q000209:etiology*; D014815:Vitamins / Q000008:administration & dosage; D055815:Young Adult
chemical_list: D010281:Parathyroid Hormone; D013473:Sunscreening Agents; D014815:Vitamins; D014807:Vitamin D; C104450:25-hydroxyvitamin D