title: Serum 25-hydroxyvitamin D concentrations fluctuate seasonally in young adults of diverse ancestry living in Toronto.
abstract: Previous research indicates that circulating vitamin D levels are low in many otherwise healthy adults and that there is considerable seasonal variation in 25-hydroxyvitamin D [25(OH)D] concentrations at high latitudes. We examined seasonal variation in 25(OH)D levels in a sample of young adults of diverse ancestry living in the Greater Toronto Area. Three hundred and fifty-one (351) healthy young adults completed both a fall and winter visit during this study. The study was conducted over 2 y (y 1: fall 2007 to winter 2008 and y 2: fall 2008 to winter 2009). At both visits, each participant's serum 25(OH)D concentration was measured. Information was also obtained on skin pigmentation (measured via reflectometer), vitamin D intake, and extent of sun exposure. Overall, the serum 25(OH)D concentration was 54.4 ± 1.3 nmol/L in the fall and 38.4 ± 1.1 nmol/L in the winter. Concentrations differed among ancestral groups at both visits (P < 0.001), with South Asians and East Asians having substantially lower concentrations than Europeans. Skin pigmentation (r(2) = 0.14; P < 0.001), supplemental vitamin D intake (r(2) = 0.09; P < 0.001), sun exposure (r(2) = 0.04; P < 0.001), and study year (r(2) = 0.02; P = 0.017) were predictors of fall 25(OH)D concentrations. During the wintertime, serum 25(OH)D concentrations were associated with concentrations taken in the fall (r(2) = 0.45; P < 0.001), supplemental (r(2) = 0.15; P < 0.001) and dietary vitamin D intake (r(2) = 0.06; P < 0.001), and with study year (r(2) = 0.02; P = 0.009). Our study confirms that serum 25(OH)D concentrations undergo strong seasonal variation at high latitudes and are influenced by vitamin D intake, skin pigmentation, and sun exposure.
authors.affiliation: Department of Anthropology, University of Toronto at Mississauga, Mississauga, Ontario, Canada.
authors.forename: Agnes
authors.initials: A
authors.lastname: Gozdzik
authors.forename: Jodi L
authors.initials: JL
authors.lastname: Barta
authors.forename: Alison
authors.initials: A
authors.lastname: Weir
authors.forename: David E C
authors.initials: DE
authors.lastname: Cole
authors.forename: Reinhold
authors.initials: R
authors.lastname: Vieth
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Whiting
authors.forename: Esteban J
authors.initials: EJ
authors.lastname: Parra
mesh_terms: D000293:Adolescent; D000328:Adult; D002853:Chromatography, Liquid; D005260:Female; D006801:Humans; D008297:Male; D009864:Ontario; D012016:Reference Values; D012621:Seasons; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D