The Vitamin D Levels You Actually Need for Fertility: What the Research Shows
We often think about vitamin D as the “sunshine vitamin” for bone health, as the skin synthesizes it naturally when exposed to ultraviolet-B (UVB) rays from the sun, but it is so much more than just that.1 Vitamin D is a fat-soluble vitamin and steroid hormone that is indeed derived from sunlight exposure, as well as from supplements and a few foods, known for exerting many important roles within the body.2,3 Commonly known for its role in maintaining calcium, bone health, and supporting immune and muscle function, vitamin D, via its active form of calcitriol (1,25(OH)2D3) plays a major role in fertility and reproduction.3
How does vitamin D impact fertility?
Within the reproductive system, vitamin D acts more like a hormone and less like “just” a vitamin. It’s involved in the fundamentals of reproduction, playing a role in ovarian production of reproductive hormones (steroidogenesis), sperm production (spermatogenesis) and follicular maturation (folliculogenesis). Its levels have also been linked with ovarian reserve, with deficiencies connected to reduced anti-Mullerian (AMH) levels, as well as sperm quality, highlighting the importance of maintaining adequate levels.3
The female and male reproductive tracts are rich in vitamin D receptors, meaning vitamin D acts directly on reproductive tissues to influence how they function. By binding to these receptors in target female reproductive tissues like the uterus and ovaries, vitamin D supports calcium absorption, helps convert cholesterol into steroid hormones like progesterone and estrogen, and contributes to immune modulation. In the male reproductive system, those receptors are expressed in Sertoli, Leydig and germ cells to drive sperm production. Because its influence on these tissues is direct, low vitamin D can impact many stages of fertility, including ovarian function, embryo development, and implantation.3
Its connection to fertility is perhaps best demonstrated through Polycystic Ovarian Syndrome (PCOS), a common hormonal disorder characterized by irregular periods, polycystic ovaries, and excess androgen levels (hyperandrogenism). A review found that vitamin D deficiency was common among women with PCOS, with 67-85% of women reporting vitamin D levels below 20 ng/mL.4 These low levels were also associated with insulin resistance, menstrual irregularities, hyperandrogenism, and increased cardiovascular risk factors.3 Vitamin D supplementation showed potential across these conditions by improving menstrual regularity and folliculogenesis, while lowering testosterone levels.3
A small randomized control trial also found an association between higher vitamin D levels and a significant increase in ovulation rates among women with PCOS, as well as significantly lower ovarian reserve in those who were deficient.3 Supplementation again appeared to improve outcomes: a prospective cohort study found that for each 10 ng/mL increase in vitamin D, fertilization rates increased by 10%, while women with deficient levels below 20 ng/mL saw a 45% reduction in fertilization rates compared to those with levels between 30 and 40 ng/mL.3
Are “normal” levels enough?
What constitutes “normal” levels of vitamin D? You might be surprised to find that what’s normal and what’s optimal are very different values. Current guidelines state that serum levels of 20 ng/mL are sufficient for most individuals, while serum levels of less than 12 ng/mL put people at risk for deficiency, yet much of the fertility research suggests that levels higher than even the standard “sufficient” levels may be needed to support fertility.2,3 But these numbers still don’t tell us what levels are needed to optimize fertility, or health in general.
The honest truth is that there isn’t an agreed-upon, set optimal level or range. For fertility, levels between 30 and 40 ng/mL may be more optimal as suggested by a prospective cohort study. This study demonstrated that women with vitamin D levels below 20 ng/mL experienced a 45% reduction in fertilization rates compared to women with levels between 30 and 40 ng/mL. So, while 20 ng/mL may technically be above deficiency, aiming for at least 30 ng/mL appears to be more supportive of reproductive outcomes.3
The best way to keep tabs on your vitamin D levels will be to ask your doctor for a 25(OH)D blood test. If your levels are borderline sufficient, talk to your doctor about supplementation.
What are the best ways to get vitamin D?
Vitamin D is primarily synthesized in the skin from sunlight, which occurs when UVB rays trigger the production of vitamin D3, accounting for 90% of our total vitamin D. The remaining 10% is found only in a few food sources, including fatty fish (salmon, sardines and mackerel), egg yolks, liver, cod liver oil, and fortified foods like milk.3
As sun exposure is our primary source of vitamin D, many factors can contribute to deficiency, including:
- Low sun exposure. Many people simply do not get enough sun. Sunscreen with SPFs above 30 also decreases vitamin D production by up to 97.5%.3
- Latitude and season. How far you live from the equator determines how much vitamin D your skin can make throughout the year. The farther north (i.e. Edmonton, Canada) the less vitamin D produced during winter. Places like Los Angeles and San Juan, which are at lower latitudes, can produce vitamin D year-round (elevation also helps produce vitamin D on sunny winter days).5
- Temperatures below 33 degrees Fahrenheit. Vitamin D3 production decreases when temperatures are below 33 degrees, as conversion to vitamin D3 from previtamin D is a temperature-dependent step.3,5
- Melanin. Melanin absorbs UVB, reducing the effectiveness of vitamin D production in darker-skinned individuals. As a result, individuals with more melanin require 5-10 times more sun exposure than lighter-skinned individuals to get adequate vitamin D.3
Vitamin D is available in dietary supplements containing the forms D2 (ergocalciferol) and D3 (cholecalciferol), though D3 may raise serum levels of vitamin D higher and sustain them for longer.6 Vitamin D3 is best absorbed when taken with dietary fat, and is often paired with vitamin K2 to support healthy calcium metabolism.7 Be sure to talk to your doctor before starting any supplementation regimen.
1. Nair R, Maseeh A. Vitamin D: The “Sunshine” vitamin. Journal of pharmacology & pharmacotherapeutics. April 2012. Accessed August 4, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC3356951/.
2. Office of dietary supplements - vitamin D. NIH Office of Dietary Supplements. June 27, 2025. Accessed August 4, 2026. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.
3. Van Tienhoven XA, Ruiz De Chávez Gascón J, Cano-Herrera G, et al. Vitamin D in Reproductive Health Disorders: A Narrative Review Focusing on Infertility, Endometriosis, and Polycystic Ovarian Syndrome. IJMS. 2025;26(5):2256. doi:10.3390/ijms26052256
4. Mohan A, Haider R, Fakhor H, et al. Vitamin D and polycystic ovary syndrome (PCOS): a review. Annals of Medicine & Surgery. 2023;85(7):3506-3511. doi:10.1097/MS9.0000000000000879
5. Bikle DD. Vitamin D: Production, metabolism, and mechanism of action. Endotext [Internet]. June 15, 2025. Accessed August 4, 2026. https://www.ncbi.nlm.nih.gov/books/NBK278935/.
6. Office of dietary supplements - vitamin D. NIH Office of Dietary Supplements. November 8, 2022. Accessed August 4, 2026. https://ods.od.nih.gov/factsheets/VitaminD-Consumer/.
7. Van Ballegooijen AJ, Pilz S, Tomaschitz A, Grübler MR, Verheyen N. The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review. International Journal of Endocrinology. 2017;2017:1-12. doi:10.1155/2017/7454376
The information in this article is for educational purposes only and should not replace professional advice. Always consult with a qualified expert to determine what services, if any, are right for you.
Ready to Learn More?
Connect with our experienced team to discuss your goals and create a personalized plan that's right for you.
