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.

Taking vitamin D might protect you from seasonal colds, the flu, or the worst effects of COVID-19, if you are short of vitamin D.

Research suggests that the correct level of vitamin D in your blood reduces your risk of developing lung infections. You 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.

If you have low vitamin D levels, supplements can help, according to a review of 25 clinical trials including more than 11,000 participants.

Taking too much vitamin D, however, could hurt your immunity, so don’t just load up on a supplement. You also need enough magnesium in your body, either from specific foods or supplements, to absorb the benefits of vitamin D.

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The role of vitamin D in your immune system

You are born with a system that identifies and attacks invaders. Vitamins D and A and zinc are essential to maintain your 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 the immune response.

Cytokines are the off switch of your immune system, which is important, too. An overreaction of the immune system called a cytokine storm has killed some people infected with COVID-19. Patients with severe vitamin D deficiency may be twice as likely to experience major complications from COVID-19.

Most tissues in your body have a specific vitamin D receptor, which explains why the vitamin is linked to cancer, diabetes, heart disease, as well as 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 vitamin D deficiency include:

• Dark skin
• Being elderly
• Being overweight or obese
• Living in an area with little sun
• Always using sunscreen when you go outside
• 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
• Hair loss

If you have any of those symptoms, and you have risk factors of vitamin D deficiency, ask your doctor to check your vitamin D levels.

What you can do

The best way to get Vitamin D is to expose yourself to direct sunlight for between 10 and 20 minutes at mid-day, but be careful to protect yourself from the sun's UV radiation after that. You may need more time if your skin is dark or the sun is 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. You need to drink 30 glasses of milk to match the vitamin D you can get from 10 minutes in the summer sun.

Supplements are a good idea for many people. Most of them contain D3, rather than D2. The FDA does not regulate vitamin supplements, however, and many of them 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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