High doses of vitamin D supplements could lead to fewer birth complications but reduce fertility

May 19 2016

New research has established that high doses of vitamin D supplements can lead to fewer complications during childbirth but reduce a woman's chances of getting pregnant in the first place.

Dr Gitte Bloch Rasmussen, Aarhus University Hospital, Denmark

The news was announced in Rome today by the Danish medical doctor and PhD Gitte Bloch Rasmussen, speaking at ECTS 2016, the 43rd annual congress of the European Calcified Tissue Society (ECTS).

Dr Rasmussen was reporting on trials that had been conducted among 193 women with low levels of vitamin D, who were all planning pregnancy and all attended a single centre in Aarhus, Denmark. The trials had been conducted by Dr Rasmussen with colleagues from Aarhus University Hospital, in Denmark.

Dr 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.

The 193 women were aged 20 - 40, were planning pregnancy and had levels of 25-hydroxyvitamin D (known as 25OHD, the most accurate way to measure vitamin D levels) below 50 nmol/L, which is bordering on insufficiency. Before conceiving, they were allocated to groups, one being given a 70mcg daily supplement of vitamin D3 and one a 35mcg daily dose, with matching groups given placebos. The women continued the trial until 16 weeks after birth and were evaluated for their 25OHD level, birth weight, fertility and any complications.

56% of the women conceived within 12 months, 38% in the placebo group, 29% taking the 70mcg supplement and 33% taking the 35mcg supplement. 44% did not conceive.

Dr Rasmussen continued:

We found a noticeable difference in two of the four areas we evaluated. Whilst the lower daily dose of vitamin D3 did not significantly affect the chances of pregnancy, the higher 70mcg daily supplement significantly reduced the chances of conceiving. On the other hand, supplementation showed to be beneficial on risk of complications during labour, as these were significantly less frequent in the combined vitamin D3 groups (a 23% risk) than in the placebo group (a 52% risk).

However, birth weight did not differ significantly between those treated with vitamin D3 and those receiving placebos; there were also no differences between groups on any safety measures.

Dr Rasmussen concluded:

High doses of vitamin D3 may reduce the likelihood of conceiving, but may also be associated with fewer complications during childbirth, though without improving birth weight.