Written by Rhiannon Davis. Reviewed by Jenny Wordsworth.

As winter approaches (AKA, it’s here right now) and the days grow shorter, many of us (especially in the UK) will spend less time in the sun, a key source of Vitamin D. For those trying to conceive, this is particularly important. While focus is often on factors like hormones, age, and lifestyle for fertility, Vitamin D plays a critical but often overlooked role in reproductive health. As we get less sun exposure during the colder months, understanding how much Vitamin D you need becomes even more crucial for supporting fertility.

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that your body primarily produces when your skin is exposed to sunlight. It also exists in smaller amounts in certain foods, including fatty fish, eggs, and fortified products like milk and cereals. Vitamin D helps your body absorb calcium, which is important for bone health, but its role extends far beyond that. It also plays a key role in immune function, mood regulation, and most importantly for this discussion, fertility.

Why Is Vitamin D Important for Fertility?

Recent research has found that Vitamin D influences various aspects of reproductive health in both those whose sex was recorded female and male at birth. Here’s how it works:

Vitamin D and Female Fertility

In women and people, Vitamin D is linked to the regulation of ovarian function, the production of sex hormones (like oestrogen and progesterone), and menstrual cycle regularity. In fact, studies have shown that women and people with sufficient levels of Vitamin D are more likely to ovulate regularly and, as a result, may have an easier time conceiving.

Vitamin D is also believed to improve the quality of the endometrium—the lining of the uterus—which is crucial for embryo implantation during early pregnancy. Some research has even suggested that Vitamin D deficiency could be linked to certain fertility disorders like polycystic ovary syndrome (PCOS) and endometriosis, though more studies are needed to fully understand these connections.

One study conducted on people undergoing in-vitro fertilisation (IVF) found that those with sufficient Vitamin D levels were significantly more likely to achieve pregnancy compared to those who were deficient. While this doesn’t mean that taking Vitamin D alone will lead to conception, it does suggest that maintaining optimal levels could play an important supportive role.

Vitamin D and Male Fertility

The benefits of Vitamin D aren’t limited to those whose sex was recorded female at birth. Those whose sex was recorded male at birth’s reproductive health is also influenced by this vitamin. Research has shown that men and people with higher Vitamin D levels tend to have higher testosterone levels, which are crucial for sperm production. Vitamin D has also been linked to improved sperm quality, including better sperm motility (the ability to swim) and morphology (shape).

One study found that men and people with sufficient Vitamin D levels had higher sperm motility and a better chance of fertilising an egg, making Vitamin D a key factor in male fertility as well.

How Much Vitamin D Do You Need for Fertility?

Now that we know why Vitamin D is important, the next question is: How much do you actually need?

Recommended Daily Intake

The recommended daily intake (RDI) for Vitamin D varies depending on age, sex, and life stage. For most adults, including those trying to conceive, the RDI is generally around 600–800 IU (International Units) per day. However, research shows that higher doses may be beneficial for fertility, especially if you’re deficient.

Studies suggest that maintaining Vitamin D blood levels of 30 ng/mL (nanograms per millilitre) or higher is optimal for reproductive health. To achieve this, some people may need to take a supplement, especially if they live in areas with limited sunlight or spend most of their time indoors.

Testing Your Vitamin D Levels

If you feel you may already have good Vitamin D levels, thanks to living abroad perhaps!, then it may be worth getting your Vitamin D levels tested. A simple blood test called a 25-hydroxyvitamin D test can measure your levels and determine if you’re deficient, sufficient, or even have excessive levels.

• Deficiency: Below 20 ng/mL
• Insufficiency: 20–30 ng/mL
• Optimal: 30–50 ng/mL
• Potentially Harmful: Over 60 ng/mL

For fertility, the aim should be to get your levels into the “optimal” range.

Can You Get Too Much Vitamin D?

While Vitamin D deficiency is common, it’s also possible to get too much. Over-supplementing can lead to Vitamin D toxicity, which can cause serious issues like kidney damage, elevated calcium levels, and cardiovascular problems.

Toxicity generally occurs when blood levels exceed 60 ng/mL, and this typically only happens with very high doses of supplements over time (more than 4,000 IU daily). So, if you’re considering taking a supplement and have any concerns, we always recommend checking with your doctor.

Sources of Vitamin D: Sun, Food, and Supplements

Sunlight

Sunlight is the most natural source of Vitamin D, and spending time outdoors can help your body produce what it needs. But the amount of Vitamin D you get from the sun depends on several factors, including:

• Geographic location: People living further from the equator get less UVB radiation year-round.
• Season: Sun exposure is lower during winter months, particularly in northern latitudes.
• Skin tone: Darker skin has more melanin, which reduces the skin's ability to produce Vitamin D.
• Age: Older individuals produce less Vitamin D from the same amount of sun exposure compared to younger people.

To get enough Vitamin D from sunlight, experts recommend spending around 10–30 minutes in the midday sun several times a week, depending on your skin tone and location. 

Dietary Sources

While sunlight is the primary source of Vitamin D, you can also get some from your diet. However, very few foods naturally contain Vitamin D. Here are some of the best dietary sources:

• Fatty fish (such as salmon, mackerel, and sardines)
• Cod liver oil
• Fortified milk, orange juice, and cereals
• Egg yolks
• Mushrooms exposed to UV light

Still, even a healthy diet may not provide enough Vitamin D, especially if you don’t eat these foods regularly. That’s where supplements can come in.

Supplements

For many people, taking a Vitamin D supplement is the easiest way to ensure they’re getting enough, especially if, like us, you’re stuck in the UK this winter. Most over-the-counter supplements come in two forms:

• Vitamin D2 (ergocalciferol): Derived from plants, often found in fortified foods.
• Vitamin D3 (cholecalciferol): Derived from animal sources and produced in the skin after sun exposure. This form is more effective at raising blood levels of Vitamin D.

For fertility purposes, most experts recommend Vitamin D3 as it’s more bioavailable. The dosage may range from 1,000 IU to 4,000 IU per day, depending on your current levels and needs. OVUM Time to Conceive® contains 100 mcg of Vitamin D3 equivalent to 4,000 IU as demonstrated to positively impact egg health. This is the maximum RDA in the UK so we wouldn’t recommend any additional supplementation of Vitamin alongside Time to Conceive®.

Key Takeaways

Vitamin D plays an essential role in fertility. From regulating hormone production to improving sperm quality and supporting embryo implantation, its benefits are clear. 

• Vitamin D is crucial for fertility, influencing hormone production, egg and sperm quality, and embryo implantation.
• The recommended daily intake of Vitamin D is 600–800 IU, but higher amounts may be needed to reach optimal levels for fertility.
• Blood levels of 30–50 ng/mL are considered ideal for reproductive health.
• Sunlight is the best natural source, but food and supplements can help maintain sufficient levels.
• Get your Vitamin D levels tested and consult a doctor if you’re concerned about toxicity.