title: Seasonal variations in serum 25-hydroxy vitamin D levels in a Swedish cohort.
abstract: To study seasonal inter-individual and intra-individual variations in serum 25-hydroxy vitamin D (25(OH)D) and to explore parameters associated with 25(OH)D in a healthy Swedish adult population. 540 blood donors (60 % men; mean age 41 ± 13 years) and 75 thrombocyte donors (92 % men, aged 46 ± 11 years) were included. Serum was collected during 12 months and analyzed for 25(OH)D and parathyroid hormone (S-iPTH). The blood donors answered questionnaires concerning vitamin D supplements, smoking, physical activity, sunbed use and sun holidays. Repeated serum samples were collected from the thrombocyte donors to study the intra-individual variations in S-25(OH)D. S-25(OH)D varied greatly over the year correlating with the intensity of the UV-B irradiation (r S = 0.326; p < 0.001). During January-March, a S-25(OH)D level below the thresholds of 50 and 75 nmol/L was observed in 58 and 88 %, respectively, and during July-September in 11 and 50 % (p < 0.001). S-25(OH)D was negatively correlated with body mass index and S-iPTH, but was significantly higher in holiday makers in sunny destinations, sunbed users, non-smokers, and in the physically active. The intra-individual analyses showed a mean increase in S-25(OH)D by 8 nmol/L/month between April and August. Approximately 75 % had serum 25(OH)D values <75 nmol/L during 75 % of the year and 50 % had serum 25(OH)D <50 nmol/L during 50 % of the year. Serum 25(OH)D was strongly associated with parameters related to sun exposure, but only weakly with intake of vitamin D supplements.
authors: Department of Rheumatology and Inflammation Research, Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden, Eva.Klingberg@vgregion.se.
authors: Eva
authors: E
authors: Klingberg
authors: Göran
authors: G
authors: Oleröd
authors: Jan
authors: J
authors: Konar
authors: Max
authors: M
authors: Petzold
authors: Ola
authors: O
authors: Hammarsten
mesh_terms: D000328:Adult; D000368:Aged; D001782:Blood Donors; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D012621:Seasons; D012907:Smoking / Q000378:metabolism; D055108:Sunbathing; D013472:Sunlight; D013548:Sweden / Q000453:epidemiology; D014466:Ultraviolet Rays; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D