As we head towards yet another winter facing the prospect of soaring covid rates alongside increased rates of influenza, it has never been more important to ensure that your immune system is in tip top condition.
So, is there anything you can do to help optimise your immune function to help fight off infections?
The answer is definitely ‘yes’ and research suggests that eating a good diet (rich in nutrients and fibre but low in processed foods and sugar) plus moderate exercise, getting enough sleep (8 hours per night), not smoking and managing your stress levels all support healthy immunity.
While eating a good diet may provide adequate amounts of nutrients like zinc (best sources in meat, fish, legumes, nuts and seeds) and vitamin C (in citrus fruits, peppers, strawberries, broccoli and potatoes) that are known to support healthy immune function, it is unlikely that diet alone will provide sufficient levels of vitamin D. The best dietary sources of vitamin D are from oily fish, red meat, egg yolks, liver and fortified foods like breakfast cereals - but the majority of vitamin D in our bodies is generated by the action of sunlight on our skin. Obviously, in the UK (particularly after the summer we have just had!) this may be problematic, and studies have found that up to 75% of the UK population may have sup-optimal vitamin D levels – particularly by the end of winter.
Since 2016 government advice has been that between October and March, all adults and children over the age of 5 should consider taking a vitamin D supplement of 10 micrograms per day. In addition: people with darker skins; those who are not exposed to much sunlight; breastfeeding infants; or children aged 1 to 4 should consider taking 10 micrograms of supplemental vitamin D per day all year round.
What is vitamin D and what does it do?
Vitamin D behaves like a hormone and nearly every cell in our body has receptors that interact with it. Traditionally vitamin D was known for its importance in bone health and preventing rickets, but it has become increasingly apparent that it is also an important modulator of immune function. It does this by supporting the part of our immune system which is the first line of defence against viral invaders, and also by modulating the inflammatory response.
Multiple large observational studies have documented that having a lower vitamin D level is associated with increased risk of developing: upper respiratory infections 1; influenza 2; HIV 3 4; autoimmune diseases like MS 5 and rheumatoid arthritis 6; and even Covid 7.
These studies, however, do not prove that having a lower vitamin D level is what causes the problem, and the evidence is less clear when we look at studies that examine whether administering supplemental vitamin D protects against developing infections.
So, should you take a vitamin D supplement?
The good news is that there is very good evidence that vitamin D supplementation can indeed reduce the incidence of upper respiratory infections8 particularly in those who have low baseline levels of vitamin D.
The evidence for any reduced Covid risk is however far from clear. While there is some preliminary indication that supplementing with vitamin D may reduce Covid infection rates, symptom severity and mortality9 10 11 - much more evidence is needed to prove any conclusive link. Watch this space!
In the meantime, I would suggest that in addition to regularly including vitamin D rich foods in your diet, everyone should follow current government guidelines to take 10 micrograms (400 IU) of vitamin D3 per day through the coming winter. More advice can be found on the NHS website https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
While this may be sufficient for most people, genetic variation can mean that a minority may need a higher intake to ensure optimal vitamin D status. Private testing for vitamin D levels is possible and anyone who would like to discuss this option can contact me via the reception at Personal Best.
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5. 21. Munger KL, et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA. 2006;296(23):2832–8. [PubMed] [Google Scholar]
6. 23. Merlino LA, et al. Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women’s Health Study. Arthritis Rheum. 2004;50(1):72–7. [PubMed] [Google Scholar]
11. Cangiano B., Fatti L.M., Danesi L., Gazzano G., Croci M., Vitale G., Gilardini L., Bonadonna S., Chiodini I., Caparello C.F., et al. Mortality in an Italian nursing home during COVID-19 pandemic: Correlation with gender, age, ADL, vitamin D supplementation, and limitations of the diagnostic tests. Aging. 2020;12:24522–24534. [PMC free article] [PubMed] [Google Scholar]
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