How can vitamin D help you strengthen your immune system 

Vitamin D is a superstar nutrient. It supports the health of your bones and teeth by helping the body absorb calcium and phosphate.¹ If you don’t get enough of the vitamin, your bones may become thin and brittle.²

There are other benefits. In addition to promoting brain cell and muscle activity, vitamin D also serves as one of the key building blocks of an efficient immune system.³ As a powerful antioxidant, it reduces inflammation and supports your body in the fight against bad bacteria and viruses.⁴

Perhaps a little-known fact, but vitamin D is not only something you get from food, a supplement or through exposure to sunlight.⁵ As a steroid molecule, it’s also a hormone which is activated in the livers and kidneys. It then circulates in the blood and binds to receptors which facilitates all sorts of biological processes – from supporting insulin release to controlling blood pressure.⁶

These receptors can be found in almost every cell and tissue, demonstrating how critically important vitamin D is for human health. In fact, it’s estimated that the vitamin D endocrine system regulates about three percent of the human genome and has an impact on over a thousand genes in the human body.⁷

The science behind vitamin D’s impact on immunity

When it comes to immunity, vitamin D helps regulate the activity of immune cells, triggering antiviral response that helps suppress inflammation.⁸ It works on both innate and adaptive immunity levels. The former is responsible for providing a quick response to fighting infections, while the adaptive system produces a slower but much more specialised response.⁹ Learn how both systems work and what their unique characteristics are in our recent article.

Maintaining the right level of vitamin D could strengthen the immune system¹⁰, while its deficiency could result in certain immune disorders and increase the risk of infections. Studies found a link between insufficient vitamin D levels and at least 53 different diseases, including Alzheimer’s, cancer, osteoporosis, diabetes and depression. However, deficiency is more common among the elderly¹¹, with research suggesting that vitamin D supplementation could help delay the deterioration of the immune system as you become older.¹²

Many studies have also examined vitamin D’s role in immunity against respiratory infections, showing that the nutrient is effective at building immunity against flu and colds, while people with low vitamin D levels are more likely to catch a cough, cold or other upper respiratory tract infections.¹³ A systematic review of 25 randomized controlled trials, for example, concluded that vitamin D supplementation significantly reduced the risk of acute respiratory tract infection. It does this by “tempering the damaging inflammatory response of some white blood cells, while boosting immune cells’ production of microbe-fighting proteins”.¹⁴ A sufficient intake of the vitamin is even more important in winter months when vitamin D deficiency is most prevalent and cold and flu season typically peaks.

Best natural sources of vitamin D: fatty fish and sunlight

Vitamin D is relatively hard to come by considering how important it is for our bodies to function properly. Only a few foods naturally contain vitamin D, including fatty fish like trout, salmon and tuna. Still, you’ll still have to eat a lot of fish to get the needed amount. Beef liver, egg yolks and cheese also have some vitamin D, although in smaller quantities.¹⁵

Many people won’t find food as the most reliable source of vitamin D, however, they are more likely to get the necessary levels by exposing themselves to the sun’s ultraviolet B (UVB) radiation. Around ten to thirty minutes of midday sunlight several times a week should be enough for your skin to produce the required amount of the vitamin. After the first production stage in the skin, blood transports the vitamin to the liver and then to the kidneys where it’s converted into an active form.¹⁶

Be sure to get direct sunlight on bare skin; receiving it through a window won’t do the trick as the glass absorbs nearly all UVB rays. Clouds, smog, old age or having dark-coloured skin also reduce the amount of sunlight your skin can absorb, and autumn and winter sun is typically too weak to give your body the necessary power to turn the chemicals into the precursor of the vitamin. Given all the limitations around vitamin D production, it’s not surprising that an estimated one billion people globally have inadequate levels of vitamin D while half of the population is insufficient.¹⁷

Supplements can help

For most people, the most efficient way to get enough vitamin D is with a supplement.¹⁸ Vitamin D supplements are typically available in two forms: vitamin D2, also known as ergocalciferol or pre-vitamin D, and vitamin D3, called cholecalciferol. Both forms increase vitamin D in your blood but D2 is only 50–60 percent as effective as vitamin D3.¹⁹ Vitamin D is fat-soluble and it’s best absorbed when taken with a meal that includes some fat.

What is the right dosage?

The recommended amount of vitamin D you need daily can vary by country. In Germany, for example, health professionals recommend children and adults to take 15 micrograms (or 800 IU) daily provided their body doesn’t produce the vitamin on its own.²⁰

Babies up to one year of age should also receive a daily supplement containing 8.5 to 10 micrograms of the vitamin, especially infants who are being breastfed.²¹

Too much vitamin D can cause problems

The maximum daily intake of vitamin D, set at 100 micrograms for adults, is unlikely to have any harmful effects on health. But getting very high levels or more than 4000 IU daily can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration or excessive urination.²²

High levels of vitamin D are almost always caused by consuming excessive amounts of vitamin D from dietary supplements. You cannot get too much vitamin D from sunshine because your skin regulates the amount of vitamin D it makes.²³

Learn more about other essential vitamins

Vitamin D is not the only nutrient of its type that can boost your body’s protection against viruses and bad bacteria. Learn more about these vitamins in our article, including which of them are abundant in a well-balanced diet and in which cases you could benefit from taking a supplement.

REFERENCES

1. https://www.hsph.harvard.edu/nutritionsource/vitamin-d/
2. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
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16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257661/
17. ​​https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency
18. https://www.health.harvard.edu/staying-healthy/vitamin-d-and-your-health-breaking-old-rules-raising-new-hopes
19. https://centrespringmd.com/vitamin-d-deep-dive-why-your-immune-system-isnt-protected/
20. https://www.rki.de/SharedDocs/FAQ/Vitamin_D/Vitamin_D_FAQ-Liste.html
21. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
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23. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108