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Vitamin D
8 Minutes

Is Vitamin D FAR more important than we realise?!

We are fast realising that not only is Vitamin D crucial for bone health but it also plays a role in reproduction (men and women), brain development and the immune system (1). Phew – pretty important then! In fact, it seems increasingly clear that not having enough can play a part in the root cause of many issues we face as parents/parents-to-be. Turns out – the science is increasingly recognising Vitamin D as one of the most important things. For EVERY stage of your Journey. We take a look at what you need to know. 

Vitamin D

We are fast realising that this important molecule plays a really important role throughout the journey. We are also realising that many of us are deficient. There are of course various assessments as to how many of us are lacking, but some research talks about as many as 40% of the population. Read more here. 

We take a quick look at the key roles it plays, how, why and what the science says:

Conception: ‘growing evidence supports a role of vitamin D in reproductive health.’ (1)

So turns out – vitamin D is not just a ‘vitamin’. It is actually a steroid hormone (1). The receptors for it have been found all across the reproductive organs. From the testis to the endometrium. When you have receptors present – it suggests they are there for a reason…. 

For the boys: Vitamin D: protection, quality and production! 

Although there is less conclusive evidence around its role in testosterone production, experimental studies have shown a beneficial effect of Vitamin D on male fertility. Largely related to its impact on semen quality. 

The most consistent supporting evidence lies around its impact on sperm motility.  An important part of the picture. Click here for more

We also know that it may play a crucial role in the protection of sperm. There is in fact evidence to suggest that having enough Vitamin D may be protective. Specifically against something we know is at the heart of many issues when it comes to sperm. DNA damage (or fragmentation) resulting from oxidative stress. Something that sperm cells are particularly vulnerable to. Click here for a lot more on this.

Important for implantation? 

If that wasn’t enough, Vitamin D also seems to play a role in implantation of a fertilised egg. There is a specific molecule involved in implantation (HOXA10 if you’re feeling technical!). This molecule has been found to be regulated by the active form of Vitamin D (D3) in human endometrial cells (2). So, making sure you have enough particularly around implantation is not going to be a bad idea. 

Not only that, ‘Vitamin D intake has been shown to play a role increasing the thickness of the endometrium lining in women with PCOS’ (1)

Speaking of which….

Vitamin D and Polycystic Ovarian Syndrome? 

There has been a lot of work done looking at Vitamin D and women with Polycystic Ovarian Syndrome (PCOS). Click here for more.   

We know that Vitamin D plays a role in reproduction and glucose metabolism. These are two things that are common issues for people with PCOS. Studies have suggested that approximately 67%–85% of women with PCOS have Vitamin D deficiency. Click here for more. 

It is not entirely clear cut when it comes to PCOS that it is as simple as taking a Vitamin D supplement. Results are mixed. Questions remain as to whether it is cause or effect. However, there is certainly no harm in making sure you have enough as a link does exist. 

Research is also linking low vitamin D with increased levels of inflammation. Chronic low level inflammation is common in people who suffer from PCOS as well as endometriosis. Click here for more. Chronic inflammation is not good for anyone and typically shows that the immune system is not working as it should. Speaking of which….

Vitamin D and your baby’s immune system: 

It is widely though that vitamin D plays an important role in regulation of the inflammation system (3). We know that when you have the immune system ‘firing’ at a low level constantly (as opposed to being reactive to attack) you can get problems. Including potential cell damage. Click here for more. Vitamin D has shown anti inflammatory properties. Something we want! 

It has also been shown to play a role in building your baby’s immune system: 

Some of the most interesting recent research emerging around Vitamin D is around how having enough Vitamin D during pregnancy can play a role/influence a child’s immunity later in life. Click here for more

Can it help reduce infections? 

There is evidence that having ‘enough’ during pregnancy can potentially reduce the risks around common childhood infections like ear, stomach and even asthma in early childhood. Infections that are pretty common in small people. Once again, click here for much more. 

Asthma is another condition that relates to a misfiring immune system and inflammation. Some research is linking increased chance of it developing to lower Vitamin D levels. Once again this isn’t conclusive, but there are studies ongoing to attempt to confirm. One study found a relationship between how much Vitamin D intake a mother had during pregnancy and asthma symptoms. The study found that higher levels were associated with ‘significantly’ lower odds of hospitalisation for asthma, whereas lower levels were found to be associated with the reverse. Read here for more. 

Can Vitamin D even influence brain development?! 

If that wasn’t enough. Research has been emerging around its role in brain development. Once again relating to having enough during pregnancy: 

‘The Vitamin D system is best known for its impact on bone mineral density. However optimal concentration of Vit D are also required for brain function, via its role in calcium signalling, neurotrophic and neuroprotective actions. As well as its role in neuronal differentiation, maturation and growth.’ (4) 

There have been several studies showing evidence linking not having enough Vitamin D during pregnancy impairment in cognitive outcomes related to language, motor development and general intelligence. (3)  Of course there are many factors likely at play, however a link does appear to exist. Click here to read the study in more depth. 

Ok: so we get it’s important! So how do you get enough Vitamin D? 

It seems increasingly important that getting enough Vitamin D is crucial. But, how much is ‘enough’? What are the factors that could mean you/your child don’t have enough?

Whilst it is pretty common to not have enough, you also don’t want too much (sigh!) as Vitamin D is a fat soluble vitamin which also means you should have too much either. Click here for more. Never simple is it!

Get yourself tested: 

So the first and easiest solution is when you are getting one of your many blood tests during your pregnancy is just ensure your doctor checks your level. Easy! 

It is always better to check your own (individual) levels than to wildly go around popping supplements which has become more of the norm these days. Everyone is different and there are various factors at play which can impact the amount of Vitamin D you have/can absorb. 

What impacts your own individual level of Vitamin D? 

Firstly, it may seem obvious but you can’t really get a lot via your diet. We know that the most significant source of Vitamin D is via sunlight.

Half an hour of sunlight delivers 50,000 iu of vitamin D with Caucasian skin. It’s worth being aware that skin pigmentation lowers the amount of Vitamin D synthesis that you get from UV exposure so the darker your skin the less you get. (24)

What on earth does 50,000 iu mean?! 

These numbers can be confusing – but to put into context: The 2012 recommendation from UK Chief Medical Officers and National Institute for Health and Care Excellence (NICE) guidance states that all pregnant and breastfeeding women should take 10 micrograms of vitamin D supplements daily: that’s equivalent to 400 iu.  

Another way to put into context: for the majority of women who are deficient in vitamin D, treatment for 4–6 weeks of 20,000 iu a week of Vitamin D3 (ie. around 3,000 IU/day) is recommended. 

How do you know if you’re deficient in Vitamin D? 

Get tested. Sounds simple enough but not enough people do it. We are passionate about getting people to test their own individual levels. We are all different. A blood test is the only way to really know. There is a bit of debate about the  ‘right level’ but it is broadly defined as a level of less than 37.5nmol/l. Click here for more. 

Main risk factors for being Vitamin D deficient: 

  • You live in an area with less sunlight or you spend a lot of time indoors.
  • During the winter months when the days are shorter
  • If you always cover your skin and always use high factor sunblock
  • If you have darker skin
  • If you are obese (BMI +30)
  • If you are a Vegan: eggs, oily fish are rich in Vitamin D
  • Genetics: some people have genetic abnormalities which impact how Vitamin D is metabolised and transported around the body.

How do you get more? 

Of course sun exposure is a tricky thing as we are all now more aware of the danger of too much sun! (Never easy is it?!). Everyone is different, but the good news is that you don’t need to sunbathe. Typically just 15 minutes a day in the sun, two or three times a week, should be enough in sunny weather. You only need to expose your arms and face. Of course everyone is different and it depends on your skin type, the time of day and the time of year. If in doubt, get your levels tested and avoid too much exposure particularly during the midday heat. Sun Safety is equally important.

What about Vitamin D supplements? 

Once again (sorry to keep stressing this!) speaking to your doctor and checking your levels is always good. Particularly before supplementing with anything. That being said, as above the guidelines are for Vitamin D supplementation for pregnant and breastfeeding women and the research around the benefits for many things including the immunity of a developing baby are compelling so this is definitely something important to be aware and on top of.

Vitamin D3 is the active form and the one you want. It is also fat soluble so ideally you want to take it with a fat. Click here for more. 



  1. Cermisoni GC, Alteri A: Vitamin D and Endometrium: A systematic Review of a Neglected area of Research: International Journal of Molecular Science: 2018 Aug: 19(8) 2320. 

  2. Vigano P, Lattuada D, Mangioni S: Cycling and early pregnant endometrium as a site of regulated expression of the vitamin D system: Journal of Molecular Endocrinology: 2006 Jun; 36(3):415 

  3. Liu W, Zhang L: The Anti-Inflammatory Effects of Vitamin D in Tumorigenesis: International Journal of Molecular Science: 2018 Sep: 19(9): 2736 

  4. Vinkhuyzen AAE, Eyles DW: Gestational vitamin D deficiency and autism-related traits: the Generational R Study: Molecular Psychiatry: 2018 23, 240-246

  5. Moukarzel S, Ozias M, Carlson S: Maternal Vitamin D Status and Infant Infection: MDPI Nutrients: 2018: Feb: 10(2): 111


This article is for informational purposes only. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. The information on this website has been developed following years of personal research and from referenced and sourced medical research. Before making any changes we strongly recommend you consult a healthcare professional before you begin.

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