If you're pregnant, or thinking about conceiving, you may want to have your vitamin D levels checked. A new review study suggests that low levels of the vitamin during pregnancy could spell trouble for both mother and child.
The researchers, led by Fariba Aghajafari, an assistant professor of family medicine at the University of Calgary, combed through the medical literature for previous studies that have examined the effects of the "sunshine vitamin" on pregnancy. They selected a total of 31 studies and performed a meta-analysis of the combined data.
The results, published Tuesday in the British Medical Journal, revealed that low vitamin D levels are linked to a wide range of pregnancy complications including:
A 49-per-cent increased risk of the woman developing gestational diabetes, or high blood sugar levels that can lead to excessive levels of sugar reaching the developing fetus. In some cases, the baby grows too large and may require a caesarean-section delivery.
A 79-per-cent increased chance of pre-eclampsia, or elevated blood pressure, a potentially life-threatening disorder during pregnancy.
A 187-per-cent increased risk of bacterial vaginosis, a vaginal infection that can trigger preterm labour.
An 85-per-cent increased chance of the baby being born smaller than the normal weight.
"We found that low vitamin D levels in the mom were fairly consistently associated with troubling outcomes," said the study's senior author, Dr. Doreen Rabi, an endocrinologist and assistant professor of medicine at the University of Calgary.
The risk of complications appears to rise when vitamin D levels dip below 75 nanomoles per litre of blood, "which is considered a pretty mild deficiency in Canada," noted Rabi.
In fact, Canadians are vulnerable to vitamin D insufficiency because of our high northern latitude and long winters. The main source of vitamin D is sun exposure: It is produced naturally by the body when skin is exposed to sunlight. It is also found in some foods such as vitamin-D enriched milk and some fatty fish.
During fall and winter, the sun's rays are too weak to produce vitamin D, and we bundle up against the cold, leaving very little bare skin. For most people, that means their vitamin D stores tend to run down – unless they pop supplements on a regular basis.
So should pregnant women be urged to take vitamin D pills? It is too soon for public health officials to make that recommendation, said Rabi, adding that the ideal vitamin D level during pregnancy is still not known.
"We went into this study hoping we might be able to get some insight into what's an appropriate level. And, unfortunately, given the way the data is reported, I don't think we are any further ahead."
She added that it would be unwise to launch a public health campaign until researchers can agree on how much vitamin D is required for a healthy pregnancy. "Once we know what's our goal, then perhaps regular blood testing [of vitamin D levels] may have some value."
Rabi said she hopes the new study will act as a catalyst that prompts other researchers to focus more attention on the role of vitamin D in pregnancy.
She pointed out that the latest research shows only an association – it does not prove that low vitamin D levels cause pregnancy complications.
"We owe it to women to understand what the association is,
so we can ensure that we are guiding their care in a knowledgeable and rational way," she said.
In the meantime, she said women should try to get the amount of vitamin D that's currently recommended for general health. Health Canada's daily recommended allowance for young adults is 600 International Units of Vitamin D. The federal agency also suggests Canadians should consider vitamin D supplementation at least seasonally. "Talk to your doctor about taking 1,000 international units (IU) a day during fall and winter months," Health Canada advises on its website.