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Will Vitamin D Supplements Really Protect You from Colds?

Adequate sleep and vitamin D supplements could help boost immunity against colds or the flu during the winter season.

Avoiding colds and flu is challenging. Physicians will tell you that vaccination is the only protection against influenza. Frequent hand washing is the other standard recommendation.

Unfortunately, immunization is imperfect. The CDC reported that the flu shot for 2022-2023 is about 48 percent effective overall. Hand washing is important, but it does not protect you from someone’s cough or sneeze launching airborne viral particles in your direction, resulting in colds or flu. Boosting immunity could be very helpful.

Adequate Sleep Improves Immune Response to Vaccination:

To get the most robust response from an immunization, it would be smart to get a good night’s sleep. A meta-analysis published in Current Biology compared responses to influenza and hepatitis vaccinations (Current Biology, March 13, 2023). Men who slept more than seven hours had a significantly stronger immune response than those who slept less than six.

In analyzing seven studies with information on sleep duration and immune response, the researchers found a clear link between objectively measured sleep and antibody response. In adults between 18 and 60, people sleeping less than six hours had significantly lower antibodies. This reduction was about equivalent to what one would see about two months after a vaccination due to waning antibodies.

How Do Vitamin D Supplements Affect Immunity?

Q. I have heard that vitamin D could improve immunity, but I wonder if that is true. How would you even find that out?

A. Plenty of studies demonstrate that people with low levels of vitamin D in their bloodstreams are more vulnerable to infections. During COVID, scientists in New Jersey conducted a randomized trial of vitamin D supplements among healthcare workers (Nutrients, Dec. 30, 2022).

Those taking 5,000 IU of vitamin D daily for nine months were less likely to come down with influenza-like illness. There wasn’t any difference in rates of COVID-19 infections, though. Consequently, we conclude that the impact on the immune system does not result in protection across the board.

You can learn more about healthy levels of vitamin D from our eGuide to Vitamin D and Optimal Health.

Will High-Dose Vitamin D Help You Avoid Colds?

Q. Are megadoses of vitamin D helpful? Somewhere I saw a recommendation to take 30,000 IU of vitamin D3 for three days to ramp up your immune system to fight off colds.

A. The dose you mention is way too high to take for any longer than three days! The Food and Nutrition Board warns against getting 10,000 IU (250 mcg) per day or more. It established the tolerable upper limits for adults at 4,000 IU (100 mcg) a day.

Studies have looked at the effects of doses of 2,000 IU daily to prevent infections and results are mixed. An analysis of immune-boosting dietary supplements found that vitamin D was helpful against respiratory infections in some but not all studies (Nutrients, Nov. 2022).  One study conducted with elderly Londoners actually found that large doses of vitamin D resulted in an increased risk of upper respiratory tract infections (Thorax, Oct. 2015).

Cod Liver Oil Against Colds:

There is another option. Mothers have been dosing their families with cod liver oil for hundreds of years. Although they never performed double-blind, placebo-controlled trials, they were convinced that this “tonic” offered some protection from upper respiratory infections.

Now scientists have figured out how cod liver oil might have helped. This fish product is rich in vitamin D.

Boosting Vitamin D to Prevent Colds and Respiratory Infections:

A study in the BMJ (Feb. 15, 2017) suggests that vitamin D supplements can boost resistance to respiratory infections.  The investigators analyzed 25 randomized controlled trials with more than 11,000 volunteers. What they found upon analysis is that vitamin D was most beneficial for those who had low blood levels of 25-hydroxyvitamin D at the outset.

The scientists also detected much greater protection against respiratory viruses among those who took their vitamin D supplement every day instead of once a month or once every few months (a “bolus” dose).

They conclude:

“Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection. We also show that people who are very deficient in vitamin D and those receiving daily or weekly supplementation without additional bolus doses experienced particular benefit.”

Who Might Benefit from Vitamin D Supplements?

How many people might be low enough in vitamin D to benefit from supplements? The CDC Second National Report on Biochemical Indicators of Diet and Nutrition found that almost 70 million Americans had 25-hydroxyvitamin D levels below the optimum (at least 20 ng/mL). In fact, more than 20 million tested below 12 ng/mL, a level that signals frank deficiency.

Why is vitamin D insufficiency so common? Sun exposure is the primary source for vitamin D. With concerns about skin cancer, people are covering up more, avoiding the sun and slathering on the sunscreen. This reduces the amount of vitamin D their bodies make during the summer.

In the winter, people in northern regions make little, if any, vitamin D. That’s why mothers in northern climates gave their families cod liver oil in the winter, even though they did not understand the reason it worked.

Learning More About Vitamin D:

If you would like to know more about this critical nutrient that functions as a hormone in the body, we invite you to read our Guide to Vitamin D Deficiency. You may also wish to listen to our interviews with Drs. Suzanne Steinbaum and Karen Costenbader. They make up Show 1300: How Vitamin D and Omega-3s Help Your Health.

Many physicians still believe that Americans don’t need supplements if they eat a well-balanced diet. Very few diets provide adequate levels of vitamin D, however. Consequently, people should have their level of 25-hydroxyvitamin D checked to see if it is adequate, especially during cold season.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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