The most important supplement you should take now—and all year-round

As I mentioned last week, boosting your immune system is one critical step you can—and should—take right now to protect yourself from any virus. And you can start by making sure you’re supplementing daily with vitamin D.

This critical vitamin protects you against just about every disease on the planet, as I regularly report. Plus, according to a brand-new study published in the prestigious British Medical Journal, taking it daily also significantly reduces your risk of contracting a respiratory tract virus.

I’ll tell you all about that study in a moment. But first, let’s back up…

A healthy immune system is the key to beating respiratory tract infections

A wealth of research shows that vitamin D plays a critical role in supporting your immune system—which, ultimately, is the key to fighting off any infection or virus.

When it comes to respiratory health, a strong immune system goes to work right away, in your nose and throat, to destroy viral and bacterial invaders.

Of course, sometimes, germs make it to the trachea (the “windpipe”), which connects the throat and lungs. At that point, the body starts producing special antimicrobial peptides in the fluid—called airway surface liquid (ASL)—that lines the trachea.

And…vitamin D increases the antimicrobial activity of ASL.

No wonder patients who have adequate blood levels of vitamin D (especially those with lung diseases) experience fewer and milder colds and cases of the flu in the first place!

Which brings us back to the new study I mentioned at the beginning of this Dispatch

New evidence to support daily vitamin D supplementation

For this new meta-analysis study, researchers assessed vitamin D’s effect on respiratory tract infections in 25 randomized, controlled clinical trials (RCTs) involving more than 11,000 participants.

They found that vitamin D supplementation reduced the risk of respiratory tract infections by 12 percent, on average, among all participants.

Now, I understand that may not seem like a huge boost. But when I dug deeper into the study, two more illuminating findings emerged…

First, dosing made a big difference, as always. Specifically, daily or weekly dosing worked far better than just one single, large (“bolus”) dose of vitamin D. So, men and women who took vitamin D daily or weekly reduced their risk by 19 percent, on average, with up to a 28 percent reduction in risk. On the other hand, men and women who received just one large, bolus dose of vitamin D did not reduce their risk at all.

(Personally, I never quite understood why so many doctors recommend treating their patients with a single, large dose of vitamin D. Evidence suggests that these doses cause wild fluctuations in vitamin D levels in the body, which can cause a cascade of other problems. Plus, big, single doses and wild fluctuations can actually undermine your immune system’s response to microbes that enter the respiratory tract. Does that sound like moderation?)

The second big finding to emerge from this study involved the importance of correcting an initial vitamin D deficiency or insufficiency (all too common in people today). In fact, men and women with lower blood levels of D (less than 25 nanomoles/liter [nmol/L]) at the start of the studies in this analysis reaped the biggest gains. They actually had a 47 percent lower risk, on average—and up to an 83 percent lower risk—of developing a respiratory virus!

And that’s not all…

Even those who started the study with better blood levels of D (greater than 25 nmol/L) still reduced their risk by 25 percent, on average—and by up to 40 percent.

Supplement with vitamin D during this crisis—and all year-round

The researchers concluded that improving vitamin D levels, particularly among older people, is a key public health measure. And it’s something we should all be hearing about right now—but don’t!—from government public health experts during their breathless daily briefings on the coronavirus.

In fact, in my view, we may well be better off with a daily dose of vitamin D than the daily dose we get of Commissar-for-Life Anthony Fauci of the National Institutes of Health (NIH).

So, if you don’t already take vitamin D, now’s the time to start…

I recommend supplementing year-round with 10,000 IU of vitamin D3 daily. (You can now find this dose in a convenient, highly-absorbable liquid form together with the potent marine carotenoid astaxanthin for added benefits. For more information, simply type “astaxanthin” into the top right search bar of my website.) In addition, clinical doctors I know and trust recommend taking 20,000 IU starting the first day you feel you are coming down with a respiratory infection.

As always, the goal of vitamin D supplementation is to achieve blood levels between 50 and 75 ng/mL. So, ask your doctor for a simple blood test called the 25 hydroxyvitamin D (25[OH]D) to check your levels twice a year—once toward the end of winter (like now) and again toward the end of summer.

Lastly, you can learn about all my top immune-health recommendations in my Pandemic Protection Playbook: How to become “immune ready” in every season. To learn more about this essential guide, click here now!


“Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.” BMJ, 2017; Feb 15; 356:i6583.