The recent global outbreak of covid-19 (aka Coronavirus) has the public on edge, and rightly so since at present there isn’t an effective vaccine available to prevent it or as yet an anti-viral medication to kill it, although the Coronavirus Task Force assures us those are being fast-tracked on the way.  More than 80,000 people have been infected worldwide and over 2800 people have died, granted most of them, as is often the case with viral ‘flu-like’ illnesses, are the very old and the medically infirm.  And that’s usually the case we confront annually with influenza, the difference, of course, being a reasonably effective anti-viral medication exists for the flu.

It brings to mind the physiologic truth that the best offense against infection is a good defense — i.e., a strong and responsive immune system. And while we might not yet have a targeted covid-19 killing medication, we do have our own targeted built in defense system that we can bolster with the miracle drug known as [1,25(OH)2D3] or as you probably know it better, Vitamin D.

Here’s an interesting article about the importance of maintaining adequate vitamin D levels, especially in winter.

The article tells us that vitamin D upregulates the production of immune modulating peptides in the respiratory tract, making it especially important to fend off getting a cold, the flu, or in this case covid-19. Adequate levels of Vitamin D help to make your immune system more bulletproof against viral assault.

A major reason there is a winter ‘flu season’ in North America is because we humans rely on the sun’s rays to naturally convert cholesterol in our skin to this critical vitamin/hormone that famously protects our bones and teeth but equally importantly also bolsters our immune function.  We make less of it in winter, especially in northern climes, because it’s cold and we’re bundled up and the sun’s rays are weakened because they’re coming in at a shallower angle–lower in the sky–passing through a lot more atmosphere on the way to us. Ideally, during the summer months, we would restore our vitamin D levels depleted by winter through regular skin exposure, but today’s sun-phobic recommendations to block sun exposure every time we walk outside means we end up blocking our vitamin D conversion as well.

Still, weak sun is better than no sun, so we’d encourage getting outdoors to receive as much unblocked sun exposure on face and arms as is possible every day the weather cooperates with sunny skies and less frigid temps. But remember that even a low-SPF sunscreen will block the rays that are responsible for this conversion, so a northern winter is no time to use it!

What you eat can make a difference as well. Vitamin D is found abundantly in mackerel and salmon and to a smaller degree in tuna, sardines, and anchovies. It’s plentiful in egg yolk and liver, too, and especially in cod liver oil.

For instance, we had sous-vide cooked salmon for dinner and made a delicious omelet for lunch the next day of fresh eggs, left over sous-vide cooked salmon, and cheese.

And, to be doubly on the safe side, in fall and winter we take a daily Vitamin D3/K2 supplement to boost blood levels. (Because I know someone will ask, we take Bio-Tech D3/K2 or their D3Plus product ourselves.)

In short, your best defense against respiratory illness (including covid-19) is to:

  • wash your hands often with soap and water
  • keep your hands away from nose or eyes (viruses enter through these mucus membranes)
  • get some unblocked sun on your skin as often as you can
  • eat foods high in vitamin D regularly
  • take a vitamin D3/K2 supplement daily in fall and winter

And remember, if you get a respiratory infection, strive to keep your viruses to yourself. Respiratory illnesses, including covid-19, spread through ‘droplets’ sprayed out during coughing or sneezing and through respiratory secretions (aka snot) ferried from nose, eyes, and mouth via your hands to other people’s hands or doorknobs or handles or pencils or table tops, or… You get the idea. Stay home if you can; give a wide berth to others if you can’t stay home; cough or sneeze into a tissue (preferably an anti-viral tissue if you have them) and throw it away immediately and wash your hands or use anti-microbial hand sanitizer before you touch anything else.

Stay well! Spring is almost here.


  1. “…the difference, of course, being a reasonably effective anti-viral medication exists for the flu.”

    If you’re referring to Tamiflu….isn’t this now widely understood as a case study of how pharma companies manipulate trial data to exaggerate benefits and conceal harms? Didn’t Cochrane show that the drug actually has minimal effectiveness and quite significant adverse effects, especially after the trial data was finally wrung out of Roche?


    1. Appreciate your comment. To be honest, I’ve taken Tamiflu myself a couple of times in the last decade or so and it has seemed to work to shorten the flu course in both rounds. Our grandson took it for test-positive type B flu this year and was recovered in 3 or 4 days, which is much quicker than the typical flu course. Granted those are anecdotal cases and I don’t doubt for a minute that Pharma fudges and stretches and obfuscates to make their case. I’ve written a few posts about it myself in other venues. But beyond that, all I said was ‘reasonably effective’ and the point of the article wasn’t the flu or whether Tamiflu works or doesn’t, it was the common sense ways people can protect themselves from respiratory illnesses and boost their immunity by eating good food and getting some sunshine and washing their hands. Thanks for weighing in.

  2. Yes, I was just curious about your views on Tamiflu. I also know people who believe it helped them. As with, say, depression drugs, where some believe they benefit despite a long record of essentially failed clinical trials.

    Thanks for the rare sane view about the new virus. Another (IMO) sane view, with some additional immune support suggestions (first of four posts on the topic):

    BTW, Brownstein’s very critical view of flu drugs, for what it’s worth:

  3. I do hope you’re right that vitamin D will help when it comes to this Covid-19 virus. I have a chronic respiratory condition which might make me more prone to complications should I get the virus BUT my vitamin D levels are replete at, currently, 147 nmol/L or 58.8 ng/mL. I also take vitamin K2. I’m in the UK which is just being hit by this virus.

    1. Anne~ having replete vitamin D is the goal and it’s great that you’re there. Keep you levels up; especially in winter. It’s not my opinion that vitamin D boosts immune function – there’s a wealth of good research that suggest it. Like flu or any other upper respiratory virus, the best way to avoid getting covid-19 is to wash your hands and keep them away from your nose and eyes. Clean surfaces that you can clean (especially if traveling) and sanitize your hands frequently. Don’t expose yourself more than you have to to groups of people — give sick folks a wide berth.

  4. Thanks for your informative post.
    The Vitamin D you linked to has 10,000 IU per capsule , do you recommend to take this daily or less often?
    Also do you recommend taking it with some Vitamin A or is it not necessary?
    Thank again.

    1. Jacob, what we actually take ourselves is by this company and is about 2,500 IU of D3 and 40 mcg of K2 per capsule (also has some magnesium, zinc, and boron, as it is designed for bone health.) Most adults can tolerate taking 5000 to 10,000 IU with the K2 just fine. Especially in winter. There is reputed synergy with vitamin A, which if you take something like cod liver oil you get both. I get A in my multi and eat yellow and orange veggies for carotene. Best source for D, of course, is sunshine.

  5. What dosage of D3 do you recommend? For years, when I have felt a cold coming on I will take 5000iu of vitamin D3 +500 mg vitamin C twice a day for 2-3 days. I am not as religious with it but will also take Zycam at these times. I find it usually stops the grunge in it’s tracks.

    For long-term immune boosting what dosage is prudent?

    1. That’s about right for most adults. It is important to have vitamin K with it, unless there is a specific reason a person can’t take vitamin K, which helps direct Calcium (under the influence of hormones and vitamin D) into the places like teeth and bones where it belongs and not into tissues where it doesn’t. The dose we take ourselves has 2500 IU of D and 40 mcg of K per capsule and we take at least one a day and in the winter usually two caps a day. Your mileage may vary — LOL!

  6. Hi Dr Mary Dan again – I see you are saying that 5,000 IU’s per day is tolerated by most adults. Twelve years ago when I first started taking vitamin D I took 4,000 IU’s per day over winter. I then asked my GP to test my vitamin D level and it came out at 384 nmol/L, that’s 153.6 ng/mL – way too much. Made my GP panic. I simply stopped taking the vitamin D, didn’t eat any vitamin D rich food and stayed out of the sun for two months and my level of D dropped to half, ie to around 76.8 ng/mL – the half life of vitamin D is actually two months. Ever since then I have taken 2,500 IUs per day in winter and 2,500 IUs every other day in summer and my levels of D, tested every six months, are always around 150 nmol/L or 60 ng/mL. I think that everyone is different, some people need more vitamin D and some less, and everyone needs to get their levels of D tested and then retested however often to make sure they are at the optimal level and that they stay there. I know I’m lucky that my GP does the test, many don’t bother, but there are labs which do tests which you can take in your home and send to them. (I also take vitamin K2 and vitamin A the weeks that I do not eat liver)

    1. Anne~ You are exactly right that everybody’s needs aren’t going to be the same and it is important, as you correctly point out, to test if you take a supplement. Some people will need more than others. I keep mine pretty well in the range with 2500 a day most of the year and as much as 5000 (with K2) in the winter.

  7. Thanks for a great article, MD. One minor point, in the second paragraph you wrote:
    “We make less of it in winter …… because …….. the sun’s rays are weakened because they’re coming in at a steep angle, passing through a lot more atmosphere on the way to us.”
    I’m sure you meant that the rays are coming in at a shallow angle ie the sun is lower in the sky.

    No big deal, after years of proofreading documents I know just how difficult it is to proofread your own writing. The brain sees what it expects to see, regardless of what’s actually on the page.

  8. An other great post on immune health.

    In the FB Group Optimising Nutrition I posted an article

    I received a comment from Marty Kendall: I don’t believe you can “boost” the immune system, but there are nutrients that come in our food that SUPPORT healthy immune function as discussed in these articles, over supplementation may actually cause an excessive immune response (ie. cytokine storm),which is why we encourage food first and try to help people understand that foods contain more of the nutrients that will support healthy innate immune function (there are plenty of real references in this article to outline how goo nutrition enables your immune system to function optimally) .

    Boost or support our immune system, which is correct? Your valued opinion is much appreciated

    1. Joan~ I have to say the two seem similar enough that I would be happy to use either word: boost (make stronger) or support (keep from falling or dropping). Seems like an unmeaningful splitting of hairs IMHO.

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