Suboptimal Vitamin D Levels in Pregnant Women Despite Supplement Use

Abstract

V itamin D is important at all life stages, but attaining adequate vitamin D during pregnancy may be especially important for the health of both mother and child. Vitamin D inadequacy during pregnancy has been associated with preeclampsia, the leading cause of maternal morbidity in Canada. 1,2 Poor vitamin D status during pregnancy may also adversely affect calcium homeostasis and skeletal mineralization in the unborn child. Rickets, which still occurs in Canada, is found almost exclusively in breastfed infants born to vitamin D-deficient mothers. 3 In addition, a lack of vitamin D in utero or in early life may increase the risk of type 1 diabetes, 4 asthma, 5 and low bone mass 6 later in life. Circulating 25 hydroxyvitamin D (25OHD) is the best indicator of vitamin D status as it represents vitamin D obtained from both UV skin synthesis and dietary sources. 7,8 The optimal 25OHD concentration in pregnancy is not known with certainty. In 2010, the Institute of Medicine recommended that maintaining a serum 25OHD concentration of approximately 50 nmol/L is desirable in all life-stage groups. 9 In 2007, the Canadian Pediatric Society adopted a 25OHD serum concentration of >75 nmol/L as "sufficient" for pregnant and lactating women, and infants. 10 Low 25OHD concentrations have been reported in pregnant women in several countries, 11,12 yet there are few studies of pregnant women in Canada. Factors that might predispose Canadian women to poor vitamin D status include living at high latitude, low vitamin D intakes from food, and for some individuals, darker skin pigmentation. Very few Canadian women of reproductive age achieve the Recommended Dietary Allowance of vitamin D intake of 600 IU. 9 However, over 80% of pregnant women consume a multivitamin supplement at some point during pregnancy. 13 It is unclear whether the amount of vitamin D provided in prenatal supplements, typically 400 IU, is sufficient to achieve optimal 25OHD concentrations. Given the widening spectrum of adverse maternal and child outcomes associated with a lack of vitamin D during pregnancy and the paucity of Canadian data, we measured 25OHD concentrations in an ethnically diverse sample of pregnant women living in Vancouver. We also explored the determinants of 25OHD concentration such as season, ethnicity and skin colour, as well as dietary and supplement intake of vitamin D.

Maternal vitamin D status, its associated factors and the course of pregnancy in Thai women

“…The findings suggested that in the group of women with adequate vitamin D status in the first trimester, the standard prenatal supplemental dose (400 IU/day of vitamin D) was high enough to maintain adequate vitamin D status throughout pregnancy. However, in the group with vitamin D inadequacy in the first trimester, 400 IU/day of vitamin D intake from prenatal vitamins could effectively prevent vitamin D deficiency during pregnancy, but was inadequate in preventing vitamin D insufficiency in about 20% of the women, even at a dose of 800 IU/day of vitamin D. This is consistent with previous studies that reported suboptimal vitamin D levels in pregnant women despite supplement use . Given the potential consequences of vitamin D insufficiency on health outcomes, vitamin D supplementation at higher doses may be needed for Thai women during pregnancy, especially in women with vitamin D inadequacy in the first trimester.…”

Postpartum depression, a direct and mediating risk factor for preschool wheeze in girls

“…Maternal education level, an indicator of socioeconomic status, was categorized as any university level education, compared with trade school, college, high school, or less. Intake of any vitamins during pregnancy was designated as prenatal vitamin use, the primary source of vitamin D during pregnancy for Canadian women …”

Vitamin D in pregnancy

“…Supplemented women had less VD deficiency in 3 large well-controlled cohorts (N=1539), a similar trend in one poorer quality study (N=201) and no difference in one study with an overall low rate of supplementation (N=559). [7, 16, 22, 27, 28] RCTs of VD supplementation have consistently shown success in raising 25(OH)D levels in pregnant women and neonates albeit with varying doses of 25(OH)D. [38] Only one negative trial is reported in the literature, and the dose was 400IU. All other doses were higher, ranging from 800-1000 IU/day to 100,000-200,000 IU given as one-time doses.…”

“…[26] U.S. women with lower VD dietary intake had more deficiency. [17, 27, 28] All data regarding diet are self-reported. There are no clinical trials regarding increasing VD status through dietary modification.…”