Are you getting enough vitamin D?
A couple of weeks ago I did my bi-annual vitamin D test. I usually do the test around Christmas time and then again in May; this helps me to check what the effects of winter have been to my stores and whether I need to continue supplementing for a little longer through summer. Usually my levels come back as pretty good (80-90nmol/L). Not so much this time - I was shocked to find my levels were down at 48nmol/L - below even the lab sufficiency levels!
Thinking back now, though, I realise that I can start to pinpoint the reasons. I was very irregular with my supplement through winter (mum life!), I’m still breastfeeding my 16-month-old - and like many other mums feeding older babies, he’s been feeding A LOT more since lockdown. We’re in the middle of a pandemic so my immune system is probably working harder than normal. I’m also a bit sleep deprived, a bit stressed as I adapt to life with a toddler, and I have not always eating brilliantly recently, relying on quick lunches of toast or wraps.
Is there any wonder that something, somewhere has to give?!
This is one of the ways testing can be really useful as it not only gives you an indication of that specific nutrient’s levels, but, with some digging, gives you the opportunity to work out WHY. And more often than not it comes down to - not eating well, not sleeping well, not resting well, or not moving well - and usually a combination of all four!
But what even is vitamin D, and why does it matter?
Why vitamin D is important
Despite its name, vitamin D is not actually very easily found in food. We primarily make vitamin D from sun exposure - if we’re not supplementing, 90% of our vitamin D is supplied from the sun. All cells in our body have vitamin D receptors on them; this means that vitamin D is important for all aspects of health. The more vitamin D receptors on a cell, the quicker they can get messages through to them to do their job faster and better.
One of the most important roles vitamin D has is in the formation of our bones. Vitamin D ensures that calcium is absorbed from food properly, and used correctly in the body. As a result, is has a very important role in the calcification of the skeleton. In pregnancy this is particular key later on, during the third trimester, when the foetal skeleton is forming and strengthening before birth. We place a great importance on calcium for bones, but this is pretty useless if you don’t have enough vitamin D to lay it down.
Vitamin D is also important for gut health and, by extension, immunity. Vitamin D produces local antibiotics in the gut and protects the gut lining. It plays a huge role in controlling inflammation in the body, which is an important aspect of a good immune system. While we want some inflammation to deal with infections or external assaults, it needs to be at the right level for the right amount of time (for more on immunity, see my previous blog post). In fact, low vitamin D has been linked to an increased risk for autoimmune disease, and if you think about the fact that most mums are low in vitamin D if they’re not supplementing, it’s no wonder that they are at a higher risk of autoimmune conditions in the first year postpartum. The link with the gut works the other way too - the right bacteria in the gut converts vitamin D into its active form, so good gut health is really important.
Further, vitamin D plays a role in good brain development and protection - low vitamin D is linked to cognitive impairment, depression and autism. It is important for muscle function, mood and memory, growth and development and heart health. I think you’ll agree with me that it’s a pretty important nutrient!
Why vitamin D is important during and after pregnancy
Low vitamin D during pregnancy is linked to a higher risk for pre-eclampsia, low birth weight and gestational diabetes. Babies born to mothers with low vitamin D levels are at risk for rickets which is where inadequate mineralisation in bones in the womb leads to soft bones (the equivalent is osteoporosis in adults, when the bones are brittle and break easily).
And the issue can have a long-lasting effects. A study found that children born to mothers with low vitamin D during pregnancy had their bone development hindered at 9 years old. That’s really major for something that can relatively easily be resolved.
In addition, low vitamin D during pregnancy and in early childhood is strongly associated with an increased risk of autism, asthma, type 1 diabetes, multiple sclerosis and language impairment.
Women with low levels of vitamin D transfer very low levels in the breastmilk. Current guidelines are that all breastfed babies be supplemented with vitamin D (you don’t need to if you’re formula feeding as it is fortified with vitamin D). There has been some research that a mother with sufficient levels of vitamin D can transfer, but she would need to be supplementing at quite high levels.
The problem with getting enough vitamin D
Various factors affect out ability to produce enough vitamin D from the sun, and this is the reason why deficiency of the vitamin varies so much across the globe, and why it is such a problem in the northern hemisphere.
In the UK, the sun is too low in the sky in the winter months for us to adequately make vitamin D between October and March. This means for at least half the year we cannot rely on getting vitamin D naturally. And even during summer we are likely not getting enough exposure, due to widespread sunscreen and protective clothing usage, and avoidance of the midday sun. The sun needs to be at least 45 degrees to the horizon to allow us to use its rays to make vitamin D, so when we seek shade and cover up between 11 and 3, we are missing the window of opportunity to make enough vitamin D. Having said that, protecting against sun damage is important so take these steps to get your vitamin D AND stay protected:
Protect your face with sunblock - we don’t make a lot of vitamin D on the face
Expose your belly and thighs
Sit in the sun for 20 minutes - you’ll make between 10,000-25,000IU in one session, depending on the colour of your skin
After your 20 minutes, cover up, sit in the shade and use sunscreen when you go out
Do this three times a week and you’ll be on your way to good levels of vitamin D
Obviously if you have very fair skin then you know your own skin. If you burn to a crisp in 20 minutes then it’s not a good idea to do that. What you’re looking for is half the amount of time it would take for your skin to go pink. If you burn just by poking your nose out your window then supplements are your best, just as is the case during winter for everyone.
In addition, if you have dark skin you have a six-fold increased risk for deficiency. This is due to higher levels of melanin in the skin which stops vitamin D production from the sun. This means the darker the skin, the longer the exposure to the sun you need to meet you body’s demand.
Finally, genetics plays a role too. Variations in your genes can affect you ability to absorb, transport and reliably use vitamin D in the body. Again, these can be mitigated with targeted supplementation and sun exposure, but knowing you have these genetic variations along with regular testing for vitamin D levels can help ensure you’re on the right track rather than guessing.
Testing and supplementing
In the UK, vitamin D deficiency is considered so widespread that current guidelines don’t suggest routine testing. However, if you are at a higher risk of deficiency - including if you’re pregnant or breastfeeding, then it is worth getting tested. It give you a baseline to work with so you can work out whether you need a maintenance dose or a higher dose for a limited time. And if you need a higher dose - how much and how long for? It is always better to work with a nutritionist or health practitioner on this.
Signs that might suggest you are low in vitamin D include:
bone pain
muscle weakness
fatigue
depression
frequent, recurrent infections
You can get a vitamin D test from your GP although they tend to only test if there is a clinical reason to do so. Alternatively, you can do a private test online quite cheaply and at home. Lab tests tend to set 50nmol/L as adequate, and don’t set an optimal level as there is no consensus on what optimal levels are.
When you make vitamin D from the sun, your skin has the ability to control the conversion of vitamin D to its active form, meaning that it can get rid of any excess easily without leading to toxic levels. When you supplement vitamin D externally, your body doesn’t have the ability to regulate in the same way, which is way there is a risk of toxicity at high levels of supplementation. Always work with a nutritionist or other practitioner if you are supplementing at levels above 1000IU.