The Power of D: The Role of Vitamin D in Fertility

When my husband came home from his internist visit and informed me that his vitamin D levels were low, I was unconcerned and simply chalked it up to being the latest fad in medicine.  However, as time has progressed and studies on vitamin D have filled the pages of major medical journals, my opinion has begun to shift.  A recent review article in Fertility and Sterility discussing the role of vitamin D deficiency and its impact on reproduction caused me to take a closer look at its possible role in fertility.

Vitamin D is a steroid hormone (active form is 1,25 dihydroxyvitamin D3) with receptors found throughout the body including the majority of reproductive organs such as ovary, uterus, placenta, testis, hypothalamus, and pituitary. It has been implicated in a number of pathologies affecting reproduction including endometriosis, polycystic ovarian syndrome (PCOS) and infertility. Since vitamin D is a natural immunomodulator with anti-inflammatory properties, it may be a plausible inhibitor of endometriosis. Interestingly, vitamin D receptor and vitamin D binding protein are increased in women with endometriosis, but both vitamin D supplementation and use of a vitamin D agonist lead to regression of endometriotic lesions in rat models.  In human studies, 25(OH)D levels have been inversely correlated with the degree of endometriosis and it has been suggested that women with high dietary intake of vitamin D have a decreased risk of developing the disease.

Vitamin D may also be a contributing factor in the health of PCOS patients. In one study looking at women trying to conceive, 25(OH)D levels less than 10 ng/ml predicted a reduced chance of follicular development and a reduced chance of becoming pregnant. In a subsequent study, treatment with 20,000 IUs of vitamin D weekly restored ovulation in 50% of previously oligomenorrheic PCOS women, with 4 out of 16 women desiring pregnancy, ultimately conceiving. Additionally, vitamin D supplementation in the PCOS population has been shown to improve lipid profiles, decrease androgen levels and improve blood pressure when compared to placebo.

Vitamin D may also prove to have a significant role in fertility acting on both the ovary and the endometrium.  At the ovarian level, vitamin D has been shown to enhance ovulation. It appears to work at a cellular level by altering AMH signaling, increasing FSH sensitivity and increasing progesterone production. In a recent study of patients undergoing IVF, those with adequate vitamin D levels had a higher chance of obtaining top quality embryos compared to those that were vitamin D deficient. Additionally, women with adequate vitamin D levels had higher implantation rates and clinical pregnancy rates than those with levels under 20 ng/ml.  Previous studies suggest this correlation is the result of an effect at the endometrial level, likely mediated through local immune responses.

In practice, I do not routinely measure vitamin D levels in my patients and instead find it more cost effective to simply recommend treatment to anyone interested in conceiving.  My standard recommendation would be supplementation with 2000 IUs per day and for those patients that have already had their vitamin D level tested, treatment would be started for a level less than 30 ng/ml. In addition to the potential benefits for their fertility, there is growing evidence that supplementation may improve birth outcomes and may decrease rates of obstetric complications. Although the literature is still relatively sparse when it comes to true randomized control trials, its safety, low cost and potential benefits make vitamin D supplementation seem like an advisable recommendation at this time.