麻豆传媒

In women with low vitamin D planning a pregnancy, high-dose supplements reduced birth complications but also lowered the chances of conceiving, according to a small clinical trial.

Compared with women taking a placebo supplement, those receiving 70 mcg vitamin D daily had about half the chances of conceiving (hazard ratio 0.52; 95% CI 0.31-0.87), reported lead investigator , of Aarhus University in Denmark, at the European Calcified Tissue Society .

However, complications were significantly lower in the vitamin D-treated women compared with the placebo group (23% versus 52%; P=0.005), Rasmussen said.

"Fertile women are often found to have low vitamin D levels, which are associated with low birth weight, reduced fertility, and adverse pregnancy outcomes. Our aim was to look at the effects of vitamin D supplements on these areas in women with low levels of vitamin D," Rasmussen said in a statement.

"This study reinforces data from previous studies looking at falls and fractures, which indicate that too much vitamin D can have adverse effects. This causes substantial concern regarding the incautious advocacy for high doses of vitamin D from some groups, particularly in North America," said , of The University of Auckland in New Zealand, in an email to 麻豆传媒.

"Vitamin D metabolites are biologically active compounds, the levels of which are tightly regulated. Therefore, to override these regulatory mechanisms with administration of very high doses is clearly unwise. This reinforces the view that physiological levels of vitamin D can be restored and maintained with doses of 400-800 IU/day, which have not been associated with any adverse effects," Reid said.

Rasmussen agreed. In an email to 麻豆传媒, she said, "Our findings call for caution on recommending too-high doses of vitamin D supplementation to women intending to become pregnant. It is of course important to avoid vitamin D deficiency in women planning pregnancy. For women at risk of vitamin D deficiency, I believe that a daily dose of 10 micrograms (400 IUs) should be recommend in order to avoid severe states of deficiency without causing potential adverse effects."

The double-blind, randomized, placebo-controlled trial included 193 women ages 20-40 planning to become pregnant. All study participants had vitamin D levels below 50 nmol/L (mean 43 nmol/L), which was considered borderline insufficient.

The women were randomized to receive either 70 mg (2,800 IU) vitamin D, 35 mg (1,400 IU) vitamin D, or a look-alike placebo daily before conceiving and for 16 weeks postpartum. Main outcomes were vitamin D levels, birth weight, fertility, and complications.

In the treatment groups, levels of vitamin D increased dose-dependently in response to treatment (P=0.001). A total of 108 women (56%) conceived within 12 months after randomization: 41 (38%) in the placebo group, 31 (29%) in the 70 mg group, and 36 (33%) in the 35 mg group.

Compared with placebo, 35 mg vitamin D did not significantly affect the chances of conceiving (HR 0.79; 95% CI 0.48-1.28). However, as mentioned, chances of conceiving were significantly lower in the 70 mg group (HR 0.52; 95% CI 0.31-0.87).

Birth weight did not differ significantly between the vitamin D-treated and the placebo groups. Complications during labor, including preeclampsia and postpartum bleeding, were significantly more frequent in the placebo group compared with the combined treatment groups (52% versus 23%, P=0.005). The study found no difference in other complications including pre-term birth, miscarriage, gestational diabetes, and infections, Rasmussen said.

The U.S. Institute of Medicine currently a vitamin D intake of 600 IU daily for adult men and women, including pregnant and lactating women. The institute recommends 800 IU daily for men and women older than 70.

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