Seasonal Variations in Serum 25-hydroxy Vitamin D Levels in a Swedish Cohort

Endocrine. 2015 Aug;49(3):800-8. doi: 10.1007/s12020-015-0548-3. Epub 2015 Feb 14.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Blood Donors
  • Body Mass Index
  • Cohort Studies
  • Female
  • Humans
  • Life Style
  • Male
  • Middle Aged
  • Parathyroid Hormone / blood
  • Seasons*
  • Smoking / metabolism
  • Sunbathing
  • Sunlight
  • Sweden / epidemiology
  • Ultraviolet Rays
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood

Substances

  • Parathyroid Hormone
  • Vitamin D
  • 25-hydroxyvitamin D