What more can you do about COVID? Take your vitamin D.

Since the start of the COVID crisis in early 2020, United States public health leadership has seldom discussed any potentially beneficial non-pharmaceutical interventions beyond washing, masking, distancing and testing.

Thankfully, these measures reduce the risk of getting the infection and they slow the rate of transmission. However, for people who become COVID positive, these measures do not reduce severity. They do not prevent hospitalization. And they do not prevent deaths.

Vaccinations reduce severity. However, we see breakthrough infections in double- and even triple-vaccinated people. And we are seeing a rapid rise in omicron cases in even highly vaccinated countries like Israel, Denmark and the United Kingdom.

So, in addition to vaccination, what else can we do? There is no approved answer.

As a physician, I am deeply concerned about the omission of self-care recommendations beyond vaccination. We should not frighten the public about COVID without also empowering people with constructive self-care strategies.

After vaccination, vitamin D supplementation is the best known low-cost, low-toxicity, biologically plausible self-care intervention to reduce COVID severity that is supported by peer-reviewed data and is easily implemented.

Vitamin D is actually a hormone with receptors on every cell in our body including every immune cell. Relevant, well-documented activities include anti-inflammatory, anti-viral, immune-enhancing, antioxidant and lung protection. Vitamin D regulates thousands of key genes including those for the ACE2 receptor through which the virus enters cells.

Numerous studies, both pre-COVID and during COVID, have documented severe vitamin D deficiency with markedly increased risk for adverse outcomes including intensive care unit (ICU) admission and hospital mortality.

The Centers for Disease Control (CDC) has documented that an unacceptably large percentage of Americans are severely low in vitamin D. This is especially true for people of color.

The darker one's skin, the more sun one needs to make vitamin D. And no one can make vitamin D in Minnesota during winter or during the rest of the year when indoors. Vitamin D deficiency is also unacceptably high for people who are obese, elderly, hypertensive or diabetic. These deficiency patterns match precisely the known risk factors for COVID-19 severity.

However, unlike the other risk factors, vitamin D deficiency is easily and safely corrected.

By January 2021, the scientific support for vitamin D supplementation was strong enough that former U.S. Surgeon General Richard Carmona pleaded in writing, "Don't let COVID-19 patients die with vitamin D deficiency — we can't wait for perfect evidence."

He and his co-authors wrote, "Given the safety profile of vitamin D, the 40% prevalence of vitamin D deficiency in the U.S., and the fact that this season [winter] will likely be the deadliest phase of the pandemic to date, we need to act now [January 2021]. Identifying and eradicating vitamin D deficiency with early and aggressive supplementation in COVID-19 has the potential to save thousands of lives and should be one of our highest public health priorities."

But we did not act. Leadership insisted on perfect evidence before making any recommendations. But leadership did not insist on funding for this evidence.

And now, one year and more than 300,000 U.S. COVID deaths later, we still do not have perfect evidence going into what might be yet another deadly phase of the pandemic.

But we do have significantly more supportive evidence for vitamin D supplementation from numerous peer-reviewed publications. And most are not weak. One that demonstrated a meaningfully reduced risk of hospitalization included over 80,000 patients. Most important, all the latest studies affirm the importance of vitamin D sufficiency (or supplementation) for reduced risk of both hospitalization and in-hospital mortality.

The retail cost at Costco for an adequate adult dose of vitamin D of 2,000-4,000 IU is less than 4 cents a day. This means that vitamin D replenishment or supplementation could be one of the most cost-effective medical interventions for minimizing COVID-19 morbidity and mortality.

No Minnesotan can make vitamin D from the sun until at least next April. This winter, please take your vitamin D.

Gregory A. Plotnikoff, a Minneapolis physician, is founder and medical director of Minnesota Personalized Medicine.