According to a 2021 Frontiers in Endocrinology scientific review, low vitamin D status is associated with suboptimal outcomes for both mother and baby during pregnancy and certain female hormonal issues that can affect fertility.
That said, even healthy women with no known hormonal health concerns may find it more difficult to conceive if they have lower vitamin D levels. In a 2019 Human Reproduction study, researchers found a direct relation between vitamin D status and the likelihood of conception in women trying to conceive.
Women with optimal levels of vitamin D [i.e., 25(OH)D levels above 50 ng/ml] were 3.4 times more likely to conceive within the six-month study than women clinically deficient in vitamin D [i.e., 25(OH)D levels below 20 ng/ml].
Considering a large chunk of the population is vitamin D deficient or insufficient (29% and 41% of U.S. adults, respectively), couples planning to conceive anytime soon would be wise to look into their vitamin D levels first.
And yes, I said couples—men are 50% of the conception equation, and their vitamin D status matters too. In a 2020 review from the World Journal of Men’s Health, vitamin D was found to improve sperm motility (which is a big deal for male fertility outcomes).*