Abstract
Use of hormonal contraceptives (HC) may influence total plasma concentrations of vitamin D metabolites. A likely cause is an increased synthesis of vitamin D binding protein (VDBP). Discrepant results are reported on whether the use of HC affects free concentrations of vitamin D metabolites. Aim: In a cross-sectional study, plasma concentrations of vitamin D metabolites, VDBP, and the calculated free vitamin D index in users and non-users of HC were compared and markers of calcium and bone metabolism investigated. Results: 75 Caucasian women aged 25–35 years were included during winter season. Compared with non-users (n = 23), users of HC (n = 52) had significantly higher plasma concentrations of 25-hydroxyvitamin D (25OHD) (median 84 interquartile range: [67-111] vs. 70 [47-83] nmol/L, p = 0.01), 1,25-dihydroxyvitamin D (1,25(OH)2D) (198 [163-241] vs. 158 [123-183] pmol/L, p = 0.01) and VDBP (358 [260-432] vs. 271 [179-302] µg/mL, p < 0.001). However, the calculated free indices (FI-25OHD and FI-1,25(OH)2D) were not significantly different between groups (p > 0.10). There were no significant differences in indices of calcium homeostasis (plasma concentrations of calcium, parathyroid hormone, and calcitonin, p > 0.21) or bone metabolism (plasma bone specific alkaline phosphatase, osteocalcin, and urinary NTX/creatinine ratio) between groups. In conclusion: Use of HC is associated with 13%–25% higher concentrations of total vitamin D metabolites and VDBP. This however is not reflected in indices of calcium or bone metabolism. Use of HC should be considered in the interpretation of plasma concentrations vitamin D metabolites.
Highlights
Vitamin D is obtained from endogenous synthesis in the skin in response to solar UV-B radiation and intake from the diet and supplements [1,2]
This paper reports a secondary analysis of the effects of hormonal contraceptives (HC) on vitamin D metabolism in a subset of women participating in a population based controlled cohort study, using cross-sectional data obtained at baseline
Our analyses showed significantly higher plasma concentrations of 25OHD, 1,25(OH)2D and vitamin D binding protein (VDBP) in users compared with non-users of HC, FI-25OHD and FI-1,25OH2D were not different between groups
Summary
Vitamin D (calciferol) is obtained from endogenous synthesis in the skin in response to solar UV-B radiation and intake from the diet and supplements [1,2]. Calciferol is converted to 25-hydroxyvitamin D (25OHD) in the liver and, subsequently, to its circulating biologically active form 1,25-dihydroxyvitamin D (1,25(OH)2D) in the kidney [3]. This conversion may occur in other tissues for auto- or paracrine actions [4]. 90% of 25OHD and 1,25(OH)2D is bound to vitamin D binding protein (VDBP) [5], 10% to 15% to albumin, whereas only a very small fraction (
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