Journal
ENDOCRINE
Volume 49, Issue 3, Pages 800-808Publisher
SPRINGER
DOI: 10.1007/s12020-015-0548-3
Keywords
Vitamin D; Vitamin D deficiency; Parathyroid hormone; Ultraviolet light
Categories
Funding
- Swedish Cancer Society
- Swedish Research Council
- LUA/ALF Funding at Sahlgrenska University Hospital
- Swedish Pain Foundation (SSF)
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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 +/- A 13 years) and 75 thrombocyte donors (92 % men, aged 46 +/- A 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.
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