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Vitamin D status of pregnant women in Vancouver Li, Wangyang


Obtaining adequate vitamin D during pregnancy is important for health of both mother and child. Low 25-hydroxyvitamin D (250HD) concentrations, the best indicator of vitamin D status, have been reported in pregnant women in several countries; yet, there are few studies of pregnant women in Canada. We determined vitamin D status, based on 250HD concentrations, of pregnant women living in Vancouver and explored the determinants of 250HD such as ethnicity, season and vitamin D intake. A convenience sample of 336 pregnant women was recruited from Greater Vancouver (49°N). Participants completed a demographic and lifestyle questionnaire as well as a food frequency questionnaire to estimate vitamin D intake. A blood sample was collected and analyzed for plasma 250HD and parathyroid hormone (PTH). Overall the mean (95% CI) 250HD was 66.7 (64.2, 69.1) nmol/L. Only 1% of women had a 250HD concentration indicative of deficiency (<25 nmol/L). However; 24% and 65% of women were vitamin D insufficient based on cutoffs of 50 and 75 nmol/L, respectively. Over 90% of women took vitamin D containing supplements and the median intake of vitamin D from food and supplements was 16.0 μg/d. In adjusted analysis, women of European ethnicity had higher mean 250HD concentrations than women of Other ethnicity [69.1 (62.8, 75.3) cf. 59.0 (52.2, 65.8) nmol/L; P = 0.004]. However, there were no differences between Europeans, Chinese, and South Asians. Mean 250HD was lower in winter [55.1 (47.7, 62.5) nmol/L] than spring [64.7 (57.7, 71.7) nmol/L] and summer [67.4 (59.9, 74.9) nmol/L] but not fall [63.2 (55.6, 70.8) nmol/L]. Only 5% of women had elevated PTH concentrations (>6.4 nmol/L) and plasma PTH was only weakly inversely related to 250HD) (R² = 0.034; P = 0.001) with no apparent inflection point. Despite high supplement use, vitamin D insufficiency appears to be common in this group of pregnant women. Ethnicity and season were determinants of 250HD but the magnitude of their effect was less pronounced than in other studies. Strategies to improve the vitamin D status of pregnant women may be required, such as increasing the amount of vitamin D in maternal supplements.

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