When I was a child, I remember walking in Paris when I came across a one-man-band. He was playing the harmonica and the guitar at the same time. He had a drum in front of him and a tambourine on his side too.

The result was stunning. I remember wanting to start dancing and singing with him (totally out of tune of course. I was only 7 afterall!). I was fascinated at how one person could manage not just to play so many instruments but could manage to play all of them at the same time. Most importantly, the result was harmonious, with each part working together to produce incredible music.

Vitamin D is a bit like that artist I saw years ago. Just like that one-man-band needed to stay in tune with each instrument to get a harmonious result, vitamin D is needed at different steps in the cycle to ensure a healthy pregnancy. In this article, we will have a look at:

– What the links between vitamin D and fertility are

– How much vitamin D you need to support pregnancy

– How you can ensure that you have the right level of vitamin D

Vitamin D affects several areas in the reproductive cycle.

Vitamin D has traditionally been associated with rickets in children and bones issues. However, in recent years, receptors for vitamin D have been found all over the body. This suggests that vitamin D could be involved in preventing some cancers, diabetes, allergies and some autoimmune diseases. Lower vitamin D levels have also been found to affect fertility.

Vitamin D for fertility
Vitamin D affects fertility on many different levels.

Several studies show that lower vitamin D levels are associated with lower pregnancy rates and lower live birth rates, both when women are getting pregnant naturally and with IVF. This could be because a higher vitamin D level increases AMH (Anti-Mullerian Hormone) levels. Some studies have also linked vitamin D with the uterine lining, possibly making it more receptive to the embryo and improving implantation rates.

Vitamin D is also essential in preventing miscarriages. One study showed that adequate vitamin D levels reduce miscarriages in women having a frozen embryo transfer. Another study from the National Institute of Health revealed a direct correlation between vitamin D levels and the risk of miscarriage.

Low vitamin D levels have been associated with PCOS. Supplementation with vitamin D could improve insulin resistance (one of the main factors in PCOS) and reduce androgen levels (e.g. testosterone) in women with PCOS

Not being deficient in vitamin D doesn’t mean having an adequate level of vitamin D.

If you have ever had your vitamin D levels checked, your GP will have probably told you that your levels are adequate if they are over 50nmol/l (sometimes even at 30nmol/l). This limit marks the value under which Western Medicine consider we are likely to become ill. For example, if vitamin D level is below 30nmol/l, one is more likely to develop rickets. Not being ill is also the benchmark used to establish how much vitamin D we need daily (400IU is our RDA because that’s the amount that protects us from rickets). However, this isn’t representative of an adequate level of vitamin D.

One way to look at it is to look at how adequate oil level helps an engine runs smoothly. If you were to check the oil level in your car’s engine, you could do it in different ways.

  • You can wait until the red light comes on the dashboard to tell you the levels are dangerously low. This is what the 30nmol/l (deficiency) limit is.
  • You can look at the engine’s oil dipstick and check it’s on or slightly above the lower line. This would be the 50nmol/l (insufficient) limit for your vitamin D. We know the engine won’t be damaged. But it might not always be lubricated enough.
  • You can decide you want to be sure that the oil level is well between the two lines so that the engine always has enough oil to run smoothly. This is when your vitamin D levels would be higher, between the 50nmol/l and 200nmol/l.

There isn’t a lot of studies looking at the impact of levels higher than 50nmol/l on fertility, but the miscarriage study mentioned above makes a direct link between miscarriages rates and vitamin D levels. From that, it seems that a level of 75nmol/l should be the minimum. According to another study, levels of 100nmol/l are needed for the optimal development of the placenta.

This means, cut off levels for fertility and miscarriage prevention are instead:

      • Below 50nmol/l: Deficient
      • Between 50nmol/l and 75nmol/l: Insufficient
      • Optimal: 100nmol/l

You can get vitamin D from sun exposure and supplementation.

Dubbed the sunshine vitamin, we usually get most of our vitamin D from sun exposure. However, the reduced amount of sun in the UK, as well as the use of sunscreen, means we often can’t get all our vitamin D from the sun, especially at levels higher than 50nmol/l.

To make the best of our sunshine, we need to be in the sun every day for at least 9 minutes at lunchtime. Between March and September, arms and legs need to be exposed, whereas, during the winter months, only the face and hands need to be exposed. This study was done on for white Caucasian in the UK. People who have darker skin tone will have more issues producing vitamin D at our latitude. This is the reason why so many people with Asian background have a blood level of vitamin D below 30nmol/l in the UK.


Vitamn D for fertility
Sitting in the sun at lunch is probably the best way to get our Vitamin D but it is unlikely to be enough to reach adequate levels for fertility


When it comes to supplementation, there is a wide variation on how much one will need. This depends a lot of what is the starting point. It is not the same to want to increase vitamin D levels from 60nmol/l than from 30nmol/l. Weight can also make a big difference in how much you will need. It might mean that you need a ‘loading dose’ with high level for a week before moving onto a maintenance dose. But the best is to work with a nutritionist who will be able to say how much you need.

As a very rough guide, a dose of 400IU should be enough to ensure you are reaching the minimum of 30nmol/l and 1000IU to achieve 50nmol/l. Any dose over 10.000IU has a much higher potential for adverse effects.

One word of caution: More isn’t always better

And this is undoubtedly true with vitamin D supplementation. Just as much as adequate vitamin D levels are essential to fertility, going overboard and taking too much vitamin D can be detrimental to health and fertility. Unfortunately, it isn’t unusual to read in forums etc… women advising each other about taking very high amounts of vitamin D in a bid to get their vitamin D levels as high as possible.

The problem here is that vitamin D also helps the body absorb calcium from food. Very high levels of vitamin D in the blood might also be linked with increased calcium levels in the blood. This calcium could then deposit in blood vessels, making them harder. In very severe cases, excess vitamin D can be toxic and lead to death.

At the same time, the solution to that is quite simple. It is vital to test vitamin D levels before supplementing, especially with high doses. After 3 months of supplementation, a subsequent blood test can tell where the blood levels are and allow for adjustments.

In summary, vitamin D is essential to fertility.

  • Adequate vitamin D levels improve fertility and reduce the risk of miscarriage
  • Optimal levels of vitamin D is around 100nmol/l
  • It is possible to get vitamin D from the sun, but it can be hard to do in the UK.
  • It is best to supplement in vitamin D only after checking your levels. This will allow your practitioner to establish how much vitamin D is suitable for you.

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