The vast majority of women who have difficulty conceiving have insufficient levels (less than 30 ng/ml) of vitamin D. It’s been debated as to whether that’s a problem because vitamin D receptors are found in the endometrium and a handful of studies have shown that women with extremely low levels of vitamin D experience lower embryo implantation rates. On the otherhand, studies have looked at this from a variety of angles but with often conflicting conclusions.
This month's Journal of Human Reproduction published a meta-analysis of the five best run trials examining the subject. The studies did a nice job collecting vitamin D serum (in the blood) levels before a woman’s treatment and recorded the most relevant endpoint, Live Birth Rate (LBR). What’s more, the studies used were from a variety of clinic locations and patient types, which is a strength when trying to determine if these results can be universally applied.
What the Study Showed
Women who had a sufficient level of vitamin D were over 30% more likely to have an IVF cycle that led to a live birth. This comes after correcting for such confounders like age and underlying diagnosis. It appears that higher pregnancy rates drove the improvement (as opposed to lower miscarriage rates) and lends credence to the notion vitamin D has a role to play in implantation.
This is a meta-analysis, which requires selecting a number of studies to include in the analysis and then pooling the different datasets to come up with a finding. This creates a few issues. The most important of which is we cannot say whether the groups being compared, aside from their varying vitamin D levels, are otherwise similar. This makes it slightly harder to attribute the differences found here to the varying vitamin D levels, or possibly some other factor.