Vitamin D (Fertility Context)

Vitamin D is a vitamin that the body converts into a hormone. It is fat-soluble, so the body stores it in fat tissue. The liver first converts it into 25-hydroxyvitamin D. This is the form a blood test measures. The kidneys then convert it into the active hormone (1,25-dihydroxyvitamin D). The active form binds to vitamin D receptors (VDRs) on cells. It helps regulate immune function, inflammation, and reproduction.

These receptors are present in the ovaries, the uterus, and the endometrium, the lining of the uterus. They are also present in the testes and in sperm. For this reason, vitamin D is relevant for both partners.¹ In men, better vitamin D status is linked with better semen quality.¹

Vitamin D before pregnancy also matters for women. One study followed 1,191 women with a previous pregnancy loss as they tried to conceive. Women with sufficient vitamin D before conception were more likely to have a live birth. They were also less likely to miscarry.² Vitamin D levels at 8 weeks of pregnancy did not show this association. RRM clinicians may check vitamin D as part of a couple's health review before conception. Goals are individual, not one number for everyone.