Vitamin D - why it’s essential for supporting your immune health this winter


Our immune system is a complex system that defends us against bacterial and viral threats from our environment. And it will do this well when it is supported by our nutrition and lifestyle.


Both ageing and chronic disease (like obesity and auto-immune issues) are associated with reduced immune function but there are still things we can do to reduce our vulnerability.


Vitamin D is at the top of the list for supporting our immune system and here I explain why.


What is Vitamin D?

Vitamin D is one of the fat-soluble vitamins (A, D E, K). There are two main forms: D2 and D3. UVB rays of sunlight increase D3 levels.


But vitamin D is actually a steroid hormone.


What is vitamin D good for?

it’s anti-inflammatory

it’s an antioxidant

it’s immune-modulatory – which means it supports your immune system

it enhances the production of defensins (your body’s natural antibiotic)


How can vitamin D help support our immune system?

Vitamin D3 is primarily produced from the action of UVB sunlight on cholesterol under the skin. An enzyme (the vitamin D binding protein) transports the D3 to the liver where it changes to 25(OHD)D – the inactive form of vitamin D. Then it goes to the kidneys where it is changed again to 1,25(OH)D – its active form.


This same enzyme that activates vitamin D is also present in bone, skin, the colon, the brain and most importantly in macrophages. Macrophages are white blood cells that are critical to our immune defence system. Vitamin D can support our immune health by increasing our supply of macrophages, which in turn help to fight infection.


This makes vitamin D one of our best lines of defence against infection.


Vitamin D deficiency has been shown to increase risk of acute respiratory distress syndrome (ARDS), one of the main complications of covid-19 infection.


There is also an association between low vitamin D levels and susceptibility to viral infections such as influenza.


Vitamin D – Testing and Supplementing

Research shows that daily supplementation of vitamin D has a protective effect in those with low vitamin D levels, cutting respiratory infection by 50%.


So how do you know how much you need?

The British Society for Ecological Medicine recommends a vitamin D blood level of at least 75 nmol/L for immune support and levels over 100 nmol/L to lower your risk of cancer and autoimmune disease.


I recommend that you test – this is the best way to see how deficient you are, and how much you then need on a daily basis to optimise your levels.


Testing involves a simple at-home finger-prick blood test. If this is something you would like to do then please drop me an email and I can arrange this for you. You will also get a personalised daily dose recommendation to help you achieve your optimal level, and my advice on the best vitamin D supplement for you.


And if you still aren’t convinced that you need to test your levels and supplement with vitamin D, read on for a whole plethora of reasons why you might be deficient and what symptoms might be attributable to low vitamin D levels.


14 signs you might have a vitamin D deficiency

1. Depression or anxiety (including mood changes or irritability)

2. Bone softening (low bone density), fractures

3. Feeling tired all the time/ decreased performance/insomnia

4. Muscle cramps and weakness

5. Joint pain (especially back and knees)

6. Difficulty regulating your blood sugar levels/ post lunch energy crash

7. Low immunity

8. Slow wound healing

9. Low calcium levels in the blood

10. Unexplained weight gain

11. Loss of appetite

12. Diarrhoea

13. Vision problems

14. Burning sensation in the mouth and throat


Why are our levels so low?

The amount the skin can produce decreases from your early 20s and will have decreased by 75% by age 70.


So, as we age, we can naturally become deficient.


There are also other lifestyle factors that can reduce our vitamin D levels:



• Sun cream. Your body makes vitamin D after contact with the sun’s UV rays but, as we’re a nation of sun cream fanatics (and this covers the skin, blocking the rays of sunlight from getting through), you might not be getting enough straight-up sun.


• Age. Among other things that go a bit wrong as you get older, your body is less good at turning the rays from the sun into vitamin D. Specifically, the kidneys are less good with age at turning it to the active form of calcitriol.

• Kidney or liver disease of any kind also means vitamin D is not converted to the active form.


• Tummy troubles. Problems with the digestive system (and I’m not talking about disease here – just an imbalance that may cause anything from a few manageable symptoms to more serious trouble ‘downstairs’) mean the digestive tract does not absorb the vitamin D as well.



• Obesity (technically that’s a BMI or body mass index of 30+) has the fat cells in your body hoover up the vitamin D. So then it’s stored – unusable – in your fat cells and is not whizzing around your body in your blood.


• Lack of sleep. Just as you need sunlight to make vitamin D, you need sleep to actually use it.


• Stress. The presence of the stress hormone cortisol reduces the uptake of vitamin D by special vitamin D receptors. It literally sits there, in the body, without being able to be used. What a waste!


• Your skin colour. The darker your skin, the less vitamin D you will make. This is due to the higher levels of melanin in your skin that protect against UV light. By blocking the sun’s rays, it also curbs the body’s ability to make the pre-cursor to the active vitamin D.


• Nightshift workers and anyone else who doesn’t spend much time in the sunlight, including children wearing sun cream all the time and babies. Quite simply, you need the sun on your skin.


How to support vitamin D levels with nutrition

Eat naturally vitamin D-rich foods


• oily fish (salmon, sardines, fresh tuna, trout, halibut, mackerel)

• high quality cod liver oil

• egg yolks

• liver


Do not be fooled into thinking that fortified foods are the same or have similar benefits. Fortified foods (like cereals, margarine and some yoghurts) contain a synthetic version of the vitamin known as D2 (the natural form is D3). Research shows this is less effective at raising levels of vitamin D in the blood.


Ready to get your vitamin D level tested?


Contact me for details and receive your personalised recommendations for daily dose and advice on the best quality supplement for you.

annali@annalicourtnutrition.co.uk


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