Seasonal variations in serum 25-hydroxy vitamin D levels in a Swedish cohort.

Eva Klingberg,Max Petzold,Göran Oleröd,Jan Konar,Ola Hammarsten

doi:10.1007/s12020-015-0548-3

Eva Klingberg, Max Petzold + Show 3 more

Open Access

https://doi.org/10.1007/s12020-015-0548-3

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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.

Highlights

Vitamin D is essential for the skeletal metabolism, muscle function, calcium homeostasis, and the immune system
The Commission Internationale de l’Eclairage (CIE)-weighted UV radiation increased from 0.36 Wh/ m2 in December to 24.25 Wh/m2 in July and was positively correlated with serum 25(OH)D Great variations were found in the mean concentrations of 25(OH)D during the different months of the year (Table 2 and Fig. 1)
25(OH)D 25-hydroxy vitamin D, BMI body mass index a Physically active defined as performing physical exercise regularly at least once a week b estrogens were taken as contraceptives or hormone replacement therapy

Summary

Introduction

Vitamin D is essential for the skeletal metabolism, muscle function, calcium homeostasis, and the immune system. At northern latitudes, the ultraviolet irradiance is too low to allow the photolysis of vitamin D during the winter months and the populations are dependent on the vitamin D consumed through food or supplements [11,12,13]. Osteomalacia occurs at low levels of 25(OH)D, usually below 25 nmol/L, but there is currently no consensus on the optimum levels of vitamin D. Adequate vitamin D status (‘‘vitamin D sufficiency’’) can be defined as the level where the serum parathyroid hormone (PTH) is stable and does not decrease further with vitamin D supplementation, which corresponds to a serum level of 25(OH)D of around 75 nmol/L [15,16,17]

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