Vitamin D and Immunity

Make sure you have enough of the sunshine vitamin — there are clear links between vitamin D and resistance to lung infections. But be careful of how much you take.

Will taking vitamin D protect you from seasonal colds, flu, or from the worst effects of COVID-19, the novel coronavirus that emerged in 2020 and spread across the world?

The answer may be yes — if you are short of vitamin D. Much research suggests that the correct level of vitamin D in your blood cuts your risk of developing lung infections. We get vitamin D mainly from exposure to sun, which is one reason people are more vulnerable to colds and viruses during winter in climates where they may not be getting enough sunlight. And if you have low vitamin D levels, supplements can help, according to a 2017 review of 25 trials including more than 11,000 participants.

Patients with severe vitamin D deficiency may be twice as likely to experience major complications from COVID-19.

Taking too much vitamin D, however, could actually hurt your immunity, so don’t just load up on a supplement.

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The role of vitamin D in the immune system

We are born with a system to identify and attack invaders. Vitamins D and A and zinc are all essential to maintaining the innate immune system.

Vitamin D is also involved in the adaptive immune system, which triggers and governs a long list of chemicals that respond to threats, including cytokines. Vitamin D regulates cytokine production, and Treg cells that suppress immune response. cytokines are the off switch, which is important, too. An overreaction of the immune system called a cytokine storm has killed some people infected with COVID-19. 

Most tissues in the body have a specific vitamin D receptor, which explains why the vitamin is linked to cancer, diabetes, and heart disease, as well as possible inflammatory bowel disease.

How do I know if I have a correct vitamin D level?

Vitamin D deficiency is very common, especially among Hispanics and African-Americans. The recommended daily intake is about 400 to 800 IU, but doctors may recommend as much as 1000 to 4000 IU a day.

The risk factors for a deficiency include: dark skin, being elderly or overweight or obese, living in an area with little sun, always using sunscreen when you go out, or staying indoors.

Symptoms of vitamin D deficiency include frequent colds and flus, fatigue during the day despite enough sleep, muscle pain, depression, slow wound healing, and hair loss.

If any of these symptoms have bothered you, and you have any of the risk factors, ask your doctor to check your vitamin D levels.

How can I raise my vitamin D level?

The best way is to expose yourself to direct sunlight for between 10 and 20 minutes at mid-day, but be careful to protect yourself from teh sun's UV radiation after that. You may need more time if your skin is dark or the sun weak. Don’t wear sunscreen for that short period. You produce “D3” or “cholecalciferol,” a precursor of vitamin D, in about half the time it takes before your skin turns pink — so you can get what you need without risking a burn.

The ultra-violet light that triggers vitamin D production doesn’t make it through windows, so your sunny breakfast nook won’t do the trick. Also, don’t count on a sun-lamp. Many of them don’t emit the ultraviolet light you need, and if they do, increase your risk of skin cancer, although the Vitamin D Lamp, approved by the Food and Drug Administration (FDA), may help.

Drinking milk and eating oily fish will help, but most people in northern climates won’t get enough that way. To match the vitamin D you can get from 10 minutes in the summer sun requires drinking 30 glasses of milk.

So, supplements are a good idea for many people. Most of them contain D3, rather than D2. However, vitamin supplements are not regulated by the FDA and may not contain what the label specifies or be vaguely labeled. For an independent review of vitamin D supplements by brand, check ConsumerLab.com. One tablespoon (14 grams) of cod liver oil contains more than three times the recommended daily amount of vitamin D.

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