Vitamin D Prevents Colds And Flu

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Nobody likes to get sick.

Yesterday a new study was published in the British Medical Journal. The results indicate that supplementation with Vitamin D may reduce the risk of acute respiratory tract infection.

To anyone in the nutrition field, this isn’t really news.

We’ve been talking about vitamin D to support the immune system for many years.

I started supplementing with vitamin D after completing a nutrition course in 2012 that emphasized the importance of vitamin D for immune health (among other things).

Let’s look at the latest study that’s assessed the benefits of Vitamin D:

The Study

vitamin-D-capsulesThere wasn’t any experimentation done in this study, as this was a systematic review and meta-analysis of previous studies done on vitamin D supplementation.

A meta-analysis evaluates previous research to try to find the general consensus about a topic using relevant criteria.

In this case, the authors used double-blind (the researcher and the subjects didn’t know whether or not they were getting the supplement) placebo-controlled (some subjects didn’t get any supplements) studies.

They used Vitamin D3 and Vitamin D2, two forms of supplemental vitamin D.

This study analyzed 25 previous studies that fit the criteria. Nearly 11,000 people from ages 0 to 95 were part of these studies.

What Does This Study Tell Us?

Certainly, a deficiency of any nutrient will have side effects.

In the case of vitamin D, low blood levels of the nutrient result in a depressed immune system and an increased risk of of acute respiratory tract infections.

The doses used in all of the studies (If you’re so inclined, the full reference list is HERE) were found to be safe.

What Did The Researchers Conclude?

vitamin-D-studyThe authors concluded that the observed benefits of vitamin D for acute respiratory infection support the need for public health measures like vitamin D fortification.

This may be better at the public level, but I prefer recommending foods naturally high in vitamin D.

Fatty fish (tuna, mackerel, sardines, salmon), liver, egg yolks, and cheese fit the bill.

The fat fears of the 1990s, and the prevailing myth that fat is bad, may have contributed to lower vitamin D intakes.

Limitations Of The Study

I find it interesting that there was no separation between the two forms of vitamin D, D2 and D3.

D3 is the preferred form, as it’s more easily absorbed by the body.

Perhaps the results would be even more convincing if only D3 was used.

The researchers admit that they only focussed on larger trials of vitamin D.

Small studies showing adverse effects from Vitamin D may have escaped their attention. They felt these studies would not have numerically affected the overall outcome.

Who Benefits Most?

Based on the body of research, it appears that vitamin D deficiency depresses the immune system and leaves the body weak against viral infections. No one wants to be sick, and it results in lost work productivity (not to mention miserable moods!).vitamin-D-Study

The best way to get vitamin D is through exposure to sunlight.

Your skin produces vitamin D when sunlight hits your skin.

This presents a problem for those of us in Northern Latitudes that don’t get sun exposure for the winter months of the year.

Even during the summer season, many people don’t get outside regularly. The elderly or incapacitated, who are usually indoors, are most likely to suffer from vitamin D deficiency.

They are also most likely to suffer poor outcomes, and potentially even death, from flu or anther viral infection.

People with darker skin are more likely to have issues with vitamin D.

The skin pigment, melanin, absorbs UVB and determines the number of photons that reach the lower cellular layers of the skin. That’s where vitamin D3 synthesis takes place.

InĀ one study, 60% of urban schoolchildren in the US were found to have deficient blood levels of Vitamin D. The problem was greatest in blacks (74.5%), Asians (Chinese, Indian, Nepalese – 88.9%), and Hispanics (64.7%). Whites and multi-racial/other were at 52.7%.


Since vitamin D is a fat-soluble nutrient, you don’t want to take too much.

An excess of any nutrient (even water!) can be dangerous.

It’s always best to have your blood levels of vitamin D tested before supplementing.

If your blood levels are good you can save yourself some cash.

If your blood levels are low, you notice a reduction in colds and flu when you start supplementing with vitamin D.


The RDA (recommended dietary allowance) for vitamin D is ridiculously low in most countries.

Health Canada, for instance, recommends 600IU of vitamin D per day for children over 1 year old and adults up to age 70.

They allow 800IU for adults over 70.

The recognized safe daily upper limit is 4,000IU.

Most multivitamins have at least the 600IU.

Whether you should take additional vitamin D depends on your blood level. It also depends on your (and your doctor’s) level of comfort.

The Last Word

Vitamin D’s role in strengthening the immune system isn’t new.

We’ve been aware that having adequate Vitamin D levels decreases the risk of viral infections for a while.

The latest study is a good summary of the body of evidence with respect to Vitamin D. If you suffer from frequent respiratory tract infections like colds and flu, you might want to see your doctor to get your blood levels of Vitamin D tested.

It may be the supplement that makes the difference for you.

Ivana Chapman

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Ivana Chapman

Ivana Chapman

Ivana Chapman BSc BA CSCS is a Canadian fitness and nutrition coach, happy wife, and mom to an energetic 6-year-old boy. She is a writer, published fitness model, speaker, 3rd Dan black belt in Shotokan Karate, former World Cup Karate Champion, one-time marathoner, and CBBF National level Natural Bikini competitor. She loves weight training and chocolate, not always in that order of preference.
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