Why vitamin D is the “must-have” supplement you need in your medicine cabinet this winter

I’ve been shouting from the rooftops for years now that everyone should be getting their vitamin D levels tested on a regular basis. But unfortunately, the message must not be getting out there as loudly or clearly as I’d like. Otherwise, why would 80 percent of Americans still be deficient in this essential nutrient?

The dangers of low vitamin D levels are quite broad—including a heightened risk of cancer, bone fractures, heart disease, and cognitive decline. And now, a new study shines a spotlight on a particularly urgent threat facing us this winter, in particular…

Most COVID-19 patients are D deficient

I’ve talked before about the unique threat that low levels of vitamin D pose in this pandemic—including a higher risk of severe complications and death. And now, new research underscores that lethal link in bold, red ink.

A recent study in the Journal of Clinical Endocrinology & Metabolism reported on more than 200 COVID-19 patients at Hospital Universitario Marqués de Valdecilla in Spain. And it found that more than 80 percent of these patients were critically deficient in vitamin D.1

On the whole, men had lower levels of vitamin D than women. And COVID-19 patients with low vitamin D levels were also more likely to have higher levels of key inflammatory markers, like ferritin and D-dimer.

Of course, there’s absolutely nothing surprising in these findings. But with another daylight savings behind us—and a long winter of colder, shorter days ahead of us—there’s no time like the present to check your vitamin D levels… and reevaluate your supplement dosage.

High doses aren’t just safe—they’re necessary

First things first, you should find out your current levels to get an idea of where you’re starting. If your doctor hasn’t given you a 25-hydroxyvitamin D test recently (or ever), make an appointment and ask for one now. (I also recommend getting your levels screened every six months to ensure you are maintaining optimal levels.)

Just bear in mind that most labs will indicate a level of 30 ng/mL is sufficient. But as I often report, that just isn’t good enough. I like my patients’ levels to be between 80 and 100 ng/mL—because really, that’s where all the health benefits kick in. You’ll most likely need at least 2,000 IU (50 mcg) to 5,000 IU (125 mcg) of D3 per day to maintain those levels.

But I often prescribe as much as 10,000 IU (250 mcg) of vitamin D3 every day to my patients. (That’s what I take every day myself.) Higher doses are particularly necessary in the winter, when sunlight exposure takes a nosedive.

Supplementing with vitamin D—even in “high doses” like this—is very safe and oftentimes, necessary. And if you’re working closely with your doctor (as you should), there’s really no reason to take any less.

I test my D deficient patients every six weeks until they get where they need to be—and I test the rest of my patients at least twice per year. So, make sure your doctor does the same. Because this winter, the stakes are simply too high to cut corners.


  1. The Endocrine Society. “Over 80 percent of COVID-19 patients have vitamin D deficiency, study finds: Vitamin D deficiency was more prevalent in men.” Science Daily, 10/27/2020. (sciencedaily.com/releases/2020/10/201027092216.htm)