While vitamin D deficiency has been shown to compromise reproduction in a number of animal models, there is currently a lack of quality human studies that specifically look at the effects of vitamin D on fertility. The majority of information currently available is based on either animal studies or observational studies with people.

Here is a review of recent research studies looking at vitamin D and fertility issues.

• In North America, sunlight exposure varies by season and location. In a review of SART data from 2007, live birth rates following donor egg embryo transfers were significantly higher in cycles done in the southwest region of the United States as compared to the northwest. The authors concluded that ecological influences might impact success.

• A 2012 report identified 68 percent of women attending a San Francisco Fertility Clinic to be either deficient or insufficient in Vitamin D. Women of Asian and/or African-American ethnicity were at greatest risk for being deficient or insufficient in vitamin D. However, when adjusted for age, vitamin D levels did not correlate with either cycle day 3 FSH or AMH levels. Pregnancy outcomes were not reported.

• Researchers at Columbia University reported in a 2012 study lower pregnancy rates in non-Hispanic whites that were Vitamin D deficient. Embryo quality and response to ovarian stimulation were not correlated with Vitamin D deficiency. The authors suggest a negative effect on the endometrium.

In addition, vitamin D deficiency has been associated with a number of fertility problems, including PCOS, endometriosis, male infertility and sperm function, and adverse pregnancy outcomes including preterm birth, gestational diabetes and preeclampsia. Still, it is not possible to say that fertility issues in either men or women will be helped by vitamin D supplementation. It is also unknown whether increasing vitamin D in the diet or by increasing sun exposure will enhance fertility.