How Much Vitamin D Do You Really Need When Trying to Conceive?

By Sarah Laver
Embryologist, Nutritionalist Advisor @the_embryologist_nutritionist

Vitamin D is a ‘vitamin’ that everyone has heard about, but did you know that it’s not actually a vitamin at all? It’s actually a prohormone; a substance the body converts into a steroid hormone before it can be used, although everyone still calls it a vitamin! It’s also not just important for bones as commonly thought, it supports fertility, the immune system, and many more areas. Now that we’ve got those two points clear, let’s discuss where you can find it, how it can support fertility, and crucially, how much do you need to help you get pregnant.

Where do we find vitamin D?

Vitamin D is known as the ‘Sunshine Vitamin’ because where we find the majority of it is when the sun’s rays meet our skin. When UVB rays hit the skin, they trigger a reaction that allows the body to produce vitamin D3. This is then activated in the liver and kidneys before the body can use it. It’s important to note that this process can be less efficient in certain cases such as: 

• people with darker skin tones - such as African, African-Caribbean, South Asian background
• use of sun cream
• people who usually cover up most of their skin when outdoors
• those that stay indoors for most of the daytime.

In these cases, it is important to look to other sources of vitamin D. Food is one of those, although it is not a very reliable source. Food sources include oily fish, eggs, fortified foods and UV-exposed mushrooms, although even these tend to provide relatively small amounts. 

The main source of vitamin D, and one that is recommended by the NHS in the UK, is via supplementation. Our ability to generate enough from the sun only happens through April to October in the UK, therefore outside of this time, and for those who may not generate enough for reasons shared previously, supplementation is recommended.

Do we need vitamin D for fertility?

Yes, this is one of the crucial micronutrients for fertility. Vitamin D receptors are found in many tissues throughout the body meaning that it is needed for just about every process taking place inside us! While research continues to explore the exact role of vitamin D in fertility, low levels are consistently associated with poorer reproductive outcomes, which is why many clinicians recommend ensuring levels are adequate before trying to conceive.

In female fertility, vitamin D appears to play a role in ovarian follicle development and hormone regulation. It is also involved in preparing the lining of the uterus and supporting the immune changes needed for implantation and early pregnancy. For the male partners, it supports the production and maturation of sperm. It also supports the body’s ability to use other nutrients such as magnesium and iron, also important in fertility. So, you can see how it is a central nutrient to optimise when trying to conceive.

How much do I need?

The NHS guidance is to supplement with 400IU every day through autumn and winter, or all year round if you fall into one of the groups mentioned earlier. However, in clinical practice what I often see is that people need a higher dosage than 400IU to optimise their blood levels. The One contains 1000 IU which may be adequate, however, my advice is TEST DON’T GUESS.

Many fertility specialists aim for blood levels around 75–100 nmol/L, with levels of <50nmol/L being classified as inadequate. 

Everyone is unique and we all produce, absorb and metabolise vitamin D differently, leading to differing needs when we consider supplementation. Vitamin D is fat soluble, which means it’s stored in fat tissue. Too much of it can become toxic so it’s important to understand how much you personally need. Your GP should be able to test and advise you on this.

Final word

Vitamin D is a small nutrient with a surprisingly wide influence on the body, including many of the processes involved in conception and early pregnancy. Supporting vitamin D status is a simple step, but it can form an important part of creating the best possible environment for both egg and sperm health.