title: Sunlight and dietary contributions to the seasonal vitamin D status of cohorts of healthy postmenopausal women living at northerly latitudes: a major cause for concern?
abstract: We assessed sunlight and dietary contributions to vitamin D status in British postmenopausal women. Our true longitudinal 25-hydroxyvitamin D (25(OH)D) measurements varied seasonally, being lower in the north compared to the south and lower in Asian women. Sunlight exposure in summer and spring provided 80% total annual intake of vitamin D.
  
  
  BACKGROUND
  Vitamin D deficiency is highlighted as a potential problem for countries at high latitude, but there are few true longitudinal, seasonal data to allow regional comparisons. We aimed to directly compare seasonal variation in vitamin D status (25(OH)D) in postmenopausal women at two northerly latitudes and to assess the relative contributions of sunlight exposure and diet.
  
  
  METHODS
  Vitamin D status was assessed in 518 postmenopausal women (age 55-70 years) in a two-centre cohort study with serum collected at fixed three-monthly intervals from summer 2006 for immunoassay measurement of 25(OH)D and parathyroid hormone. At 57° N (Aberdeen, Scotland, UK), there were 338 Caucasian women; at 51° N (Surrey, South of England, UK), there were 144 Caucasian women and 35 Asian women. UVB exposure (polysulphone film badges) and dietary vitamin D intakes (food diaries) were also estimated.
  
  
  RESULTS
  Caucasian women had lower 25(OH)D (p < 0.001) at 57° N compared to 51° N. Median (interquartile range) in nanomoles per litre for summer (June-August) at 57° N was 43.0 (20.9) and at 51° N was 62.5 (26.6) and for winter (December-February) at 57° N was 28.3 (18.9) and at 51° N was 39.9 (24.0). For Asian women at 51° N, median 25(OH)D was 24.0 (15.8) nmol/L in summer and 16.9 (15.9) nmol/L in winter. Median dietary vitamin D intakes were 80-100 IU for Caucasians and 50-65 IU for the Asian women. Sunlight was the main contributor to 25(OH)D with spring and summer providing >80% total annual intake.
  
  
  CONCLUSIONS
  These longitudinal data show significant regional and ethnic differences in UVB exposure and vitamin D status for postmenopausal women at northerly latitudes. The numbers of women who are vitamin D deficient is a major concern and public health problem.
authors.affiliation: University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, UK. h.macdonald@abdn.ac.uk
authors.forename: H M
authors.initials: HM
authors.lastname: Macdonald
authors.forename: A
authors.initials: A
authors.lastname: Mavroeidi
authors.forename: W D
authors.initials: WD
authors.lastname: Fraser
authors.forename: A L
authors.initials: AL
authors.lastname: Darling
authors.forename: A J
authors.initials: AJ
authors.lastname: Black
authors.forename: L
authors.initials: L
authors.lastname: Aucott
authors.forename: F
authors.initials: F
authors.lastname: O'Neill
authors.forename: K
authors.initials: K
authors.lastname: Hart
authors.forename: J L
authors.initials: JL
authors.lastname: Berry
authors.forename: S A
authors.initials: SA
authors.lastname: Lanham-New
authors.forename: D M
authors.initials: DM
authors.lastname: Reid
mesh_terms: D000368:Aged; D044466:Asian People; D004032:Diet; D004739:England; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D017698:Postmenopause / Q000097:blood; D012606:Scotland; D012621:Seasons; D013472:Sunlight; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood*; D044465:White People
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D