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Free and Bioavailable Fractions of Vitamin D: Association with Maternal Characteristics in Brazilian Pregnant Women

2020; Hindawi Publishing Corporation; Volume: 2020; Linguagem: Inglês

10.1155/2020/1408659

2090-0732

Joana N. Pereira, Julia Chactoura, Fernanda Nohra, Maria Eduarda Leão Diógenes, Flávia Fioruci Bezerra,

Iron Metabolism and Disorders

Normal pregnancy is characterized by many changes in vitamin D metabolism, challenging the assessment of vitamin D status based exclusively on serum total 25-hydroxyvitamin D (25(OH)D). We hypothesized that measuring free and bioavailable fractions contributes to a better vitamin D status assessment in late pregnancy. Our aim was to evaluate a broad set of biomarkers of vitamin D status in Brazilian women in the third trimester of pregnancy. This cross-sectional study was conducted in women ( n = 123, 18–44 y, 27–41 wk gestation) attended in a public maternity in Rio de Janeiro (2016–2018). Biomarkers included serum concentrations of total 25(OH)D 3 , parathyroid hormone (PTH), vitamin D-binding protein (DBP), and free and bioavailable fractions of 25(OH)D 3 . Vitamin D insufficiency (<50 nmol/L) was prevalent in 47.9% of the pregnant women. Serum 25(OH)D 3 was inversely associated with the gestational week ( β = −0.71, 95% confidence interval (CI): −1.31 to −0.16) and season, being lower in autumn ( β = −9.90, 95% CI: −16.14 to -3.64) and winter ( β = −16.74, 95%CI: −23.13 to −10.34). Concentrations of DBP, and free and bioavailable 25(OH)D 3 were also inversely associated with winter months ( P < 0.05 ). DBP was directly associated with prepregnancy BMI ( β = 5.84, 95% CI: 0.62 to 11.06). The recognized season-effect on total 25(OH)D 3 appeared to also occur on free and bioavailable fractions. Although advanced gestational age was associated with lower total 25(OH)D 3 , our results suggest an adaptive mechanism responsible for maintaining free fraction during the 3 rd trimester. We also suggest that starting pregnancy in obese condition may have an impact on vitamin D bioavailability, which deserves further investigation.