Why Is Vitamin D So Important for Fertility? Optimal Levels for Conception

Why Vitamin D Matters for Fertility

Vitamin D is technically a hormone, not just a vitamin, and it plays vital roles throughout the reproductive system¹. Vitamin D receptors are found in the ovaries, uterus, placenta, and testes, suggesting this nutrient is fundamental to reproductive function.

For a comprehensive overview of this essential nutrient, explore our article on Vitamin D: Everything You Need To Know.

Optimal Vitamin D Levels for Conception

Understanding vitamin D levels requires knowing what the numbers mean²:

• Deficient: Below 30 nmol/L (12 ng/mL)
• Insufficient: 30-50 nmol/L (12-20 ng/mL)
• Adequate: 50-75 nmol/L (20-30 ng/mL)
• Optimal for fertility: 75-150 nmol/L (30-60 ng/mL)

Research suggests that vitamin D levels of at least 75 nmol/L (30 ng/mL) are associated with better fertility outcomes. Some studies indicate that levels between 100-125 nmol/L (40-50 ng/mL) may be ideal for conception.

How Vitamin D Affects Female Fertility

Vitamin D influences multiple aspects of female reproductive health³:

Hormone Regulation

Vitamin D helps regulate the production of oestrogen and progesterone. Low levels can disrupt the delicate hormonal balance needed for regular ovulation and cycle regularity.

Egg Quality

Adequate vitamin D supports healthy egg development. The vitamin affects the mitochondria within eggs, which are crucial for fertilisation and early embryo development.

Ovarian Function

Research shows women with sufficient vitamin D levels have better ovarian reserve markers (AMH levels) and more regular ovulation patterns.

Implantation

Vitamin D receptors in the uterine lining suggest this nutrient plays a role in preparing the endometrium for implantation. Women with adequate vitamin D levels may have better-quality uterine linings.

Learn more about preparing for implantation in our article on Optimising Uterine Lining Health.

Vitamin D and PCOS

Polycystic ovary syndrome (PCOS) is strongly associated with vitamin D deficiency⁴. Low vitamin D levels in PCOS may worsen:

• Insulin resistance
• Irregular ovulation
• Elevated androgen levels
• Weight management difficulties

Supplementing vitamin D may help improve some PCOS symptoms and support more regular cycles. For more information, read our article on Folate, Vitamin D, and PCOS.

Vitamin D and Male Fertility

Vitamin D is equally important for male reproductive health⁵:

• Sperm quality: Vitamin D receptors on sperm cells influence motility and function
• Testosterone production: Adequate vitamin D supports healthy testosterone levels
• Sperm count: Studies show men with sufficient vitamin D have higher sperm concentrations
• Sperm morphology: Better vitamin D status is associated with more normally-shaped sperm

Vitamin D and IVF Success

Multiple studies have examined vitamin D levels in women undergoing IVF⁶:

• Women with adequate vitamin D (above 75 nmol/L) have significantly higher clinical pregnancy rates
• One study found vitamin D-replete women were nearly twice as likely to achieve pregnancy compared to deficient women
• Better vitamin D levels are associated with higher-quality embryos
• Implantation rates appear improved in women with sufficient vitamin D

For more on preparing for fertility treatment, explore our guide to Supplements for IVF.

How to Increase Your Vitamin D Levels

Sunlight Exposure

Your body produces vitamin D when skin is exposed to UVB rays. However, in northern latitudes, sunlight is often insufficient from October to March, making supplementation necessary.

Diet

Few foods naturally contain significant vitamin D. Good sources include:

• Oily fish (salmon, mackerel, sardines)
• Egg yolks
• Fortified foods (some cereals, milk alternatives)
• Mushrooms exposed to UV light

Diet alone rarely provides sufficient vitamin D for optimal fertility levels.

Supplementation

Most people trying to conceive will benefit from vitamin D supplementation. The NHS recommends all adults take 10mcg (400 IU) daily, but higher doses may be needed to achieve optimal fertility levels.

Our Vitamin D supplement provides an effective daily dose to help maintain optimal levels. Those with diagnosed deficiency may need higher therapeutic doses – speak to your healthcare provider about appropriate dosing.

Testing Your Vitamin D Levels

A simple blood test can measure your 25-hydroxyvitamin D [25(OH)D] level. Consider testing:

• Before starting to try to conceive
• Before beginning fertility treatment
• If you have PCOS, endometriosis, or unexplained infertility
• If you have limited sun exposure or dark skin
• Annually during autumn/winter months

Your GP can arrange testing, or you can use private fertility tests. Learn more about Female Fertility Testing options.

Vitamin D Safety Considerations

While vitamin D is essential, very high levels can be harmful. Key points:

• The safe upper limit is generally considered 100mcg (4000 IU) daily for adults
• Higher doses should only be taken under medical supervision
• Regular testing helps ensure levels remain in the optimal range
• Vitamin D3 (cholecalciferol) is the preferred form for supplementation

Supporting Nutrients

Vitamin D works best alongside other key nutrients:

• Vitamin K2: Helps direct calcium to the right places
• Magnesium: Required to convert vitamin D to its active form
• Omega-3 fatty acids: Support vitamin D absorption – our Vital DHA provides essential omega-3s

A comprehensive fertility supplement like Vitafem provides synergistic nutrients alongside vitamin D.

Frequently Asked Questions

How long does it take to increase vitamin D levels?

With appropriate supplementation, you may see improvements in 6-8 weeks, but reaching optimal levels can take 2-3 months. Consistency is key – take your supplement daily.

Can vitamin D improve egg quality?

Research suggests vitamin D supports mitochondrial function within eggs, which is crucial for fertilisation and early embryo development. Optimising levels before conception may benefit egg quality.

Should my partner also take vitamin D?

Yes, vitamin D is important for male fertility too. Men with adequate vitamin D levels have better sperm parameters. Both partners should aim for optimal levels.

Is vitamin D safe during pregnancy?

Yes, the NHS recommends 10mcg (400 IU) daily throughout pregnancy. Maintaining adequate levels supports both maternal health and foetal development.

Can you take too much vitamin D?

Vitamin D toxicity is rare but possible with very high doses over extended periods. Stay within recommended limits unless advised otherwise by your healthcare provider.

References

1. NHS. Vitamins, supplements and nutrition in pregnancy. NHS. 
2. Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266-281.
3. Fung JL, et al. Association of vitamin D intake and serum levels with fertility: results from the Lifestyle and Fertility Study. PubMed. 2017;108(2):302-311.
4. Lerchbaum E, Obermayer-Pietsch B. Vitamin D and fertility: a systematic review. Eur J Endocrinol. 2012;166(5):765-778.
5. Blomberg Jensen M. Vitamin D and male reproduction. Nat Rev Endocrinol. 2014;10(3):175-186.
6. Chu J, et al. Vitamin D and assisted reproductive treatment outcome: a systematic review and meta-analysis. Hum Reprod. 2018;33(1):65-80.

If you're concerned about your vitamin D levels or fertility, please consult your GP or a fertility specialist. This article is for informational purposes only.