Vitamin D for fertility

On this page

1. What is vitamin D?
2. Function and how it works
3. Fertility benefits
4. Recommended daily dose
5. Food sources
6. Cautions and contraindications
7. My Fertility Guide
8. Related pages

1. What is vitamin D?

Vitamin D is a fat-soluble vitamin that exists in five forms (D1, D2, D3, D4, D5). The most important for human health is vitamin D3 (cholecalciferol), which the skin makes when exposed to sunlight (when the UV index is higher than 3) without sunscreen. Most people living in cloudy countries — including the UK, Ireland, New Zealand and the east coast of the United States — are deficient in vitamin D for at least part of the year.

Even low-factor sunscreens such as SPF 8 reduce vitamin D production by 95%. Because of the genuine risk of skin cancer, the recommended approach is 10–15 minutes of unprotected sun exposure before applying sunscreen. Reference ranges and recommended intakes vary from country to country — always interpret guidance against the recommendations of your own healthcare authority.

2. Function and how it works

Vitamin D acts as a hormone in the body and influences hundreds of genes. Functions relevant to fertility include:

1. Mineral absorption. Vitamin D regulates the absorption of calcium, zinc and iron. Low vitamin D contributes to anaemia.
2. Hormone regulation. Vitamin D supports the production of fertility hormones in both men and women.
3. Immune balance. Vitamin D modulates the immune system, supporting the immune balance required for embryo implantation.
4. Anti-inflammatory effects. Vitamin D reduces chronic inflammation that can interfere with conception.
5. Sperm function. Vitamin D receptors are present on sperm, and adequate vitamin D supports sperm motility.

3. Fertility benefits

Research has shown that women with lower levels of vitamin D have reduced fertility. Adequate vitamin D supports IVF success rates, healthy pregnancy outcomes and reduced miscarriage risk. In men, vitamin D is required for healthy sperm production and motility. Most fertility patients in the UK benefit from year-round supplementation.

4. Recommended daily dose

I recommend a daily dose of 15 mcg (600 IU) in summer months and 20 mcg (800 IU) in winter months of vitamin D3 (cholecalciferol) for women trying to conceive in the UK. Some patients require considerably higher doses (1,000–2,000 IU per day) under professional supervision to correct documented deficiency — this should always be guided by blood test results.

5. Food sources

Vitamin D is difficult to obtain in adequate quantities from food alone. Sources include:

1. Sardines, herring, salmon and other oily fish
2. Eggs (the yolk)
3. Butter and full-fat dairy
4. Fortified foods (some breakfast cereals, plant milks)
5. Cod liver oil (men only when trying to conceive — vitamin A risk in pregnancy)

The body's primary source of vitamin D is sunlight on the skin — aim for 10–15 minutes of unprotected exposure to bare arms and legs in the middle of the day during summer, before applying sunscreen.

6. Cautions and contraindications

1. Excess vitamin D supplementation (sustained doses above 4,000 IU per day without medical supervision) can cause toxic levels of calcium in the blood (hypercalcaemia).
2. People with certain medical conditions (sarcoidosis, kidney disease) may need to avoid vitamin D supplements.
3. Always test vitamin D status before starting high-dose supplementation.
4. Always consult with a fertility specialist or your doctor before starting any new supplement regime.

7. My Fertility Guide

8. Related pages

• Fertility supplements directory
• Vitamin A
• Calcium
• Iron
• Zinc
• Cod liver oil