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Alterations in the vitamin D endocrine system during pregnancy: A longitudinal study of 855 healthy Norwegian women.

Alterations in the vitamin D endocrine system during pregnancy: A longitudinal study of 855 healthy Norwegian women.
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Gustafsson MK, Romundstad PR, Stafne SN, Helvik AS, Stunes AK, Mørkved S, Salvesen KÅ, Thorsby PM, Syversen U,


Gustafsson MK, Romundstad PR, Stafne SN, Helvik AS, Stunes AK, Mørkved S, Salvesen KÅ, Thorsby PM, Syversen U, (click to view)

Gustafsson MK, Romundstad PR, Stafne SN, Helvik AS, Stunes AK, Mørkved S, Salvesen KÅ, Thorsby PM, Syversen U,

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PloS one 2018 04 1113(4) e0195041 doi 10.1371/journal.pone.0195041
Abstract

To ensure optimal calcium accrual in the fetal skeleton, a substantial rise occurs in 1,25-dihydroxyvitamin D (1,25(OH)2D), but is dependent on sufficient 25-hydroxyvitamin (25(OH)D). Large longitudinal studies addressing free 25(OH)D and 1,25(OH)2D during pregnancy are scarce. We aimed to assess levels of and relationship between 25(OH)D, 1,25(OH)2D, vitamin D-binding protein (DBP), parathyroid hormone (PTH), and free 25(OH)D during pregnancy; determinants of vitamin D status; and association between vitamin D indices or PTH and pregnancy outcomes (gestational diabetes mellitus and birthweight). Altogether 855 pregnant Norwegian Caucasian women from Trondheim and Stavanger (latitude 63°N and 58°N) were recruited; 94 were lost to follow-up. The study was originally a randomized controlled trial (2007-2009) with gestational diabetes as primary outcome. Data were collected in second and third trimester. In third trimester, 246 (34%) had vitamin D insufficiency and 52 (7%) deficiency (25(OH)D <50 and <30nmol/L, respectively). During wintertime in third trimester, 61 (47%) from Trondheim and 23 (51%) from Stavanger exhibited vitamin D insufficiency. PTH was elevated in 27 (3.7%). Estimate of change between trimesters was (95% CI): 25(OH)D -1.8 (-2.8 to -0.7) nmol/L, DBP 0.62 (0.57 to 0.66) μmol/L, calculated free 25(OH)D -1.7 (-2.0 to -1.4) pmol/L, PTH 0.81 (0.72 to 0.90) pmol/L, 1,25(OH)2D (sub-analysis) 31.4 (CI 24.7 to 38.2) pmol/L. A decrease in 1,25(OH)2D occurred in 45% of those with vitamin D deficiency, and they also exhibited lower levels than women with adequate vitamin D status. No association of vitamin D indices and PTH with pregnancy outcomes was observed. Women in Trondheim displayed lower 25(OH)D levels, despite minor latitudinal differences. Less than one-fifth adhered to the authorities' vitamin D recommendations. These findings demonstrate that hypovitaminosis D is prevalent among pregnant women living in northern latitudes, especially during the dark season, and there is an unmet need to ensure adequate vitamin D intake.

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