#206 Does Vitamin D Prevent Colds? The Latest Research

Does Vitamin D Prevent Colds? The Latest Research

Vitamin D is good for your bones.  Not getting enough vitamin D has been linked to heart disease, cancer, and dementia.  But does vitamin D prevent colds?  In this article, I review the latest research looking at vitamin D, colds, the flu, and other respiratory tract infections.  If you, or a loved one, has been sick this year, you won’t want to miss this article.

My Vitamin D Challenges

As readers know, I’m not a fan of supplements unless it is for a critical nutrient or vitamin that you can’t get naturally.  For me, vitamin D fits this category.

I recently had my vitamin D level checked at the end of the summer.  I picked this time because I wanted to see what my levels were in the best possible situation.  As I often go on long mountain bike rides or trail runs during the summer, I figured my vitamin D levels would at least be normal this time of the year.

I was wrong.  Even with eating fish and a lot of sun exposure, my vitamin D level came back at 25 ng/mL.  At my hospital, the normal range for vitamin D is 30 to 80 ng/mL.

Knowing that I have a clear vitamin D deficiency that can’t be corrected naturally, I have faithfully taken a vitamin D supplement this winter.  Remarkably, even with four young children, frequent periods of sleep deprivation while being on call at the hospital, and several colds that went through our family, I have not been sick once this year.

I figured it was my healthy diet protected me against colds, the flu, and other respiratory tract infections.  But then, this study  just came out.  Based on my careful review of this study, perhaps it is my daily vitamin D supplement that is protecting me from getting sick this winter.

The Vitamin D and Colds Study

This past week in the prestigious British Medical Journal, 25 researchers from Harvard University, and other major medical centers from around, the world published their findings on vitamin D supplements and the risk of respiratory tract infections.  In this study, researchers pooled the results of 25 vitamin D studies involving 11,321 people.  Here are their four main findings:

1. Taking any vitamin D supplement reduced your risk of getting an upper respiratory tract infection by 12%.

2. Those taking a daily dose of vitamin D were 19% less likely to get an upper respiratory tract infection.

3. For people with a documented vitamin D deficiency, a daily dose of vitamin D reduced their chances of getting an upper respiratory tract infection by 70%.

4. There were no statistically significant complications of taking vitamin D observed in this study.

What does this study tell us?

The key message of this study is that a daily dose of vitamin D seems to be protective against colds and other illnesses.  However, for those with a documented vitamin D deficiency, like me, the protective effects are literally off the charts.

When the researchers looked at dosing frequency, a daily dose of vitamin D appeared to be most  protective.  This is probably because periodic big doses of vitamin D changed gene expression and other metabolic pathways.

What doesn’t this study tell us?

First, it doesn’t tell you how much vitamin D you should take.  As this study pooled the results of 25 previously published studies, the vitamin D dose used in every study was completely different.  Thus, as everyone’s need for vitamin D varies, please ask your doctor what dose is right for you.  Please note that you may not even need a supplement at all.

Second, this study didn’t find that you had to get your vitamin D above a certain level to be protected from colds or other illnesses.  Rather, just taking a daily dose of vitamin D seemed to be what was important.

How does vitamin D protect you from colds?

Many readers are probably wondering how vitamin D can keep you from getting sick.  Interestingly, vitamin D has been shown in many studies to strengthen the immune system.  With a strong immune system, bacteria and viruses don’t stand much of a chance.

Can you get too much vitamin D?

The short answer is yes.  You want to keep your vitamin D levels below 100 ng/mL.  When vitamin D levels get too high, people may suffer from high calcium levels in their blood or kidney stones.

In addition, our research has shown that the risk of a dangerous heart condition, called atrial fibrillation, shoots way up when vitamin D levels get above 100 ng/mL.  The bottom line is that if you and your physician choose to supplement with vitamin D, be sure not to overdose on vitamin D.

How can you get more vitamin D naturally?

It is always best if you can get everything your body needs naturally.  When it comes to vitamin D, your very best source is the sun.  If you have had skin cancer, or you have a family history of skin cancer, check with your physician first before spending time in the sun.

If you live far from the equator, like I do in Salt Lake City, then it is next to impossible to get any meaningful dose of vitamin D from the sun during the winter months.  If you live closer to the equator, you may be able to get year-round vitamin D from the sun.

During the summer, 15 minutes of mid-day sun is all most people need for their daily dose of vitamin D.  When the sun isn’t available, the very best food source is fish.  For example, just a 158 calorie serving of salmon (4 ounces or 113 grams) provides 128% of the vitamin D you need for the day.  Also, most milks such as cow, almond, soy, etc., are supplemented with vitamin D.

Take Home Message

The take home message of this study is that we now have pretty strong evidence that vitamin D prevents colds and other illnesses.  To get this benefit, the vitamin D supplement should be taken daily and the best results are for people with a documented vitamin D deficiency.

As vitamin D toxicity can cause heart problems or other complications, please be sure to only take vitamin D under the supervision of your physician.  For most people, they may only need a vitamin D supplement during the winter when they can’t get it naturally from the sun.

Do you take a vitamin D supplement?  Please leave your thoughts, comments, and questions below.  I’ll do my best to answer every question within 24 hours.  If you enjoyed this article, please be sure to sign up for my free weekly newsletter and podcast.

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  1. I had been taking D3-5000 iu for over two weeks. I just had my vitamin d levels checked and they were still lowl. My dr. recommended 1000 iu daily…Is that going to be enough?

    • Hi Janice,

      Thanks for reading! Keep working with your physician. By tracking your vitamin D levels you’ll be able to accurately determine how much vitamin D you really need. Everyone is different so everyone’s vitamin D needs will vary.



    • Hi Marleen,

      This is something you should discuss with your physician. You may not even need to supplement. A vitamin D level could be very helpful in determining if a vitamin D supplement is even needed.

      Hope this helps!


    • If one is vit d deficient how many IUs do you recommend a day?
      Also I saw you today. I’m the funny one that takes 1/2 of a diltiazem capsule. I forgot to ask you if you prefer calcium blockers over beta blockers & why?
      Thank you Dr. Day I think your the best! Jolene

      • Hi Jolene,

        There are so many factors which go into whether or not someone should take vitamin D supplements. Ideally, it would be helpful to know what your level is at right now and then work with your regular doctor to see if a supplement is even needed.

        Regarding calcium channel blockers vs. beta-blockers, there are many issues to consider. If heart failure is present, beta-blockers are preferred. If the heart is otherwise healthy, then either calcium channel blockers or beta-blockers could be use to treat arrhythmias.

        Hope this helps!


  2. Dear Dr John Day,

    Thanks a lot for your interesting article!
    Have you heard if taking high doses of Vitamin D (2000UI per day) could make you Magnesium deficient?
    For example in this article https://www.vitamindcouncil.org/about-vitamin-d/vitamin-d-and-other-vitamins-and-minerals/, it says to get the most of Vitamin D you need take other vitamins and minerals like: Vitamin A, K, Magnesium, Zinc, Boron. And I’m not sure if this resource is trustworthy.
    From my own experience – I was taking 5 months Vitamin D (200OUI per day) as I was Vitamin D deficient (my level was 15). At the beginning I was fine, but after the 4th and 5th month, I was tired all the time, got more headaches and palpitations.
    Do you think that might have been caused by the Vitamin D?

    • Hi Nikol,

      Thanks for reading and commenting! Yes, vitamin D levels don’t function in a vacuum. Vitamins A, K2, etc. all play a role. It would have been interesting to have seen what your vitamin D levels were after you started to get headaches and palpitations.


  3. My vitamin D levels chronically are in the 25 range. I haven’t had a cold in three years. However, it appears that even when I take a supplement of no more than 1000 daily, constipation occurs. Is this a side effect of taking vit D?