In my clinic, I regularly find that low vitamin D levels are a common thread among patients struggling with fertility, PCOS, and endometriosis. A 2025 narrative review by Ximena A. van Tienhoven et al. confirms that this isn’t just anecdotal—it’s backed by science.
Vitamin D isn’t just for bone health. It acts like a steroid hormone, affecting ovarian follicle maturation, steroid hormone regulation, endometrial receptivity, and immune modulation in reproductive tissues. That means insufficient vitamin D can influence multiple stages of fertility, from ovulation to implantation.
The review highlights that 40–50% of healthy pregnant women have vitamin D levels at or below 20 ng/mL (50 nmol/L), which is considered deficient. In my practice, I see similar rates—even among women with no obvious risk factors. It’s a reminder that testing vitamin D should be routine, not optional.
Women with PCOS often have vitamin D levels below 20 ng/mL (50 nmol/L)—estimates range between 67–85%. The review notes associations with insulin resistance, menstrual irregularities, and elevated androgens. Clinical trials also show that vitamin D supplementation may improve insulin sensitivity, lower testosterone, and regulate menstrual cycles. This aligns closely with what I see—patients reporting better cycle regularity and more predictable ovulation after correcting the deficiency.
Vitamin D’s anti-inflammatory and immunomodulatory effects may help disrupt the chronic inflammation seen in endometriosis. The authors cite studies where vitamin D reduced peritoneal immune cell activity, animal models showing slower lesion growth, and observational data linking lower vitamin D with more severe disease. In the clinic, I’ve noticed that patients with endometriosis often have low vitamin D, and some report symptom relief—less pelvic pain and improved energy—after supplementation.
Vitamin D affects ovarian reserve (e.g., AMH levels), uterine lining thickness, and embryo implantation. Several studies cited by van Tienhoven show better endometrial quality and improved live birth rates in IVF cycles. But—there are still no universal dosing guidelines or deficiency thresholds tailored to fertility.
- Test vitamin D levels early in fertility workups—especially if planning IVF, dealing with PCOS, endometriosis, or unexplained infertility.
- If deficient (≤20 ng/mL [50 nmol/L]), supplement to reach ≥30 ng/mL [75 nmol/L], usually with 2,000–4,000 IU/day, depending on baseline and seasonal factors.
- Recheck after 8–12 weeks. Aim for a maintenance range of 30–50 ng/mL [75–125 nmol/L] in peri-conception and IVF cycles (though precise thresholds remain debatable).
- Combine vitamin D with lifestyle: balanced diet (fish, egg yolks), moderate sun exposure, weight management, and co-supplements like folic acid or inositol as clinically indicated.
- Track reproductive outcomes: cycle regularity, ovulation, endometrial thickness on ultrasound, ovarian reserve markers, and IVF success rates. It’s how I tailor treatment.
Van Tienhoven’s review confirms what I observe daily: vitamin D deficiency is common in reproductive disorders and likely impacts outcomes. While we need more randomized trials to nail down exact dosing and timelines, optimizing vitamin D is a low-risk, high-reward intervention.
References:
- van Tienhoven, X. A., Gubbels, M., & van der Hoek, M. (2025). Vitamin D in reproductive health disorders: A narrative review focusing on infertility, endometriosis, and polycystic ovarian syndrome. Preprints.
https://doi.org/10.3390/ijms26052256 - Wei, S.-Q., et al. (2013). Maternal vitamin D status and adverse pregnancy outcomes: A systematic review and meta-analysis. J Matern Fetal Neonatal Med, 26(9), 889–899.
- Irani, M., et al. (2014). Vitamin D deficiency in oocyte donors is associated with lower pregnancy rates in recipients. Fertility and Sterility, 102(2), 456–460.
- Lerchbaum, E., & Obermayer-Pietsch, B. (2012). Vitamin D and fertility: A systematic review. European Journal of Endocrinology, 166(5), 765–778.
Dr Marina OBGYN