The Critical Role of Vitamin D in Immune Health


The Critical Role of Vitamin D in Immune Health

by Lt Col Chad Gregory Kahl MD SFS CMA FAAFP
CJCS/Flight Surgeon PFMC Pentagon

“O powerful western fallen star!”

Walt Whitman

Whitman, of course, was giving, a not so subtle nod, to the untimely demise of our 16th president, with his metaphorical elegy. In addition to its use repeatedly in literature and poetry as emblem of hope and spiritual renewal. Our own, powerful, western star, literally provides one of our bodies most essential vitamin hormones. Vitamin D.

Moreover, unless you are living on an island, it would have been impossible not to hear some discussion on its role in our body’s ability to fight off respiratory illnesses and other diseases.

It has been shown that 10 to 30 minutes of direct sunshine, most days per week, is required to maintain healthy vitamin D levels. But, research also shows that people spend less than 10% of their day outside, making it impossible to get the amount of sun exposure to produce adequate circulating levels of vitamin D. Complicating the equation is that darker skin types, can take 6 to 10 times longer than the lightest skin to create the same quantity of vitamin D, and that the elderly and obese are also challenged in their ability to convert Vitamin D in their skin.

While it may be too soon to recommend everyone to start increasing the amount of supplemental Vitamin D across the board, physicians and health care providers, have a responsibility to identify and correct this deficiency.

Most studies show that over 70% of Americans get less than the recommended intake of vitamin D. Moreover, while there is historic and unequivocal evidence that it is essential for bone health, there is a growing body of evidence that it plays a vital role in a healthy immune system. Research is also growing that it likely has a role in regulating insulin levels, affecting cancer outcomes, improving mental health disorders, and most timely, may even decrease the severity of COVID 19 infections.

A study highlighted on Medscape in December of 2020, showed Vitamin D deficiency on admission to hospital was associated with a nearly 4-fold increase in the odds of dying from COVID-19, based on data from the first wave of the pandemic. In this study, nearly 60% of patients with COVID-19 were vitamin D deficient upon hospitalization, with men in the advanced stages of COVID-19 pneumonia showing the greatest deficit.

In December 2020, researchers published findings in the journal Nutrients, that “athletes and people associated with them, could benefit from better athletic performance, better health, and reduced risk for COVID-19 by maintaining serum 25(OH)D concentrations above 40 ng/mL. To achieve that concentration, (it) could take supplementation of vitamin D3 at perhaps 4000–10,000 IU/day, depending on body size, skin pigmentation, and other personal factors.”

In June 2008, a study published in the Archives of Internal Medicine found that low blood levels of vitamin D were associated with a doubled risk of death overall.

At a scientific meeting in May 2008, Canadian researchers reported that vitamin D deficiency was linked to poorer outcomes in women with breast cancer.

A large study of aging in the Netherlands, published in the May 2008 issue of Archives of General Psychiatry, found a relationship between vitamin D deficiency and depression in women and men ages 65 to 95.

It’s important to note here, that promising findings from observational studies don't always pan out when put to the test in clinical trials. However, in one of the few randomized trials testing the effect of vitamin D supplements on cancer outcomes, postmenopausal women who took vitamin D plus calcium, reduced their risk of developing non-skin cancers by 77% after four years, compared with a placebo and the same dose of calcium. In addition, the small randomized pilot study from Spain in October of 2020, demonstrated that administration of a high dose of Calcifediol or 25-hydroxyvitamin D, a main metabolite of vitamin D endocrine system, significantly reduced the need for ICU treatment of patients requiring hospitalization due to proven COVID-19.

Lack of sun exposure would be less of a problem if diet provided adequate vitamin D. However, there are not many vitamin D–rich foods (see chart, below), and you need to eat a lot of them to get even 800 to 1,000 IU per day. People who have trouble absorbing dietary fat — such as those with intestinal diseases — can't get enough vitamin D from diet no matter how much they eat (vitamin D requires some dietary fat in the gut for absorption). In addition, people with liver and kidney disease are often deficient in vitamin D, because these organs are required to make the active form of the vitamin, whether it comes from the sun or from food.

Selected food sources of vitamin D

Food Vitamin D (IU*)
Salmon, 3.5 ounces 360
Mackerel, 3.5 ounces 345
Tuna, canned, 3.5 ounces 200
Orange juice, fortified, 8 ounces 100
Milk, fortified, 8 ounces 98
Breakfast cereals, fortified, 1 serving 40–100


So, the 4 trillion dollar question is; do low vitamin D levels correlate with more severe covid-19 outcomes. It is immediately obvious that there is a Vitamin D pandemic that is running parallel to the current COVID-19 Pandemic.

Most concerning, is that consistently black and brown skin populations have the highest likelihood of contracting and having severe COVID illness. This shines a shameful light on health disparities that already exist among Black, Hispanic and White patients, as darker skin populations have higher rates of Vitamin D deficiency.

So, at the very least, medical providers should immediately consider increasing the supplementation of Vitamin D in at risk populations, people of color, the elderly, the obese, diabetics, especially if those levels are currently under 20 ng/ml. Knowledge of this level can be helpful to patients in discussing the importance of the vitamin D hormone in health outcomes.

A recent letter drafted and signed by more than 185 doctors, scientists and leading authorities, including myself, have called on for increased use of vitamin D in the fight against COVID-19.

Higher vitamin D blood levels seem to be associated with lower rates of SARS-CoV-2 infection and Higher D levels seem to correlate with lower risk of a severe cases (hospitalization, ICU, or death.)

I have nearly all of my patients, taking vitamin D supplements, anywhere from 2-6000 IU a day. I myself take 5000 IU daily and have been doing so since the start of the pandemic. It’s important to express that Vitamin D is not the cure for Covid-19. However, vitamin D deficiency may create vulnerability, and having normal levels of vitamin D may help stabilize the cytokine storm, sparked by Covid-19.

As an ending note, it is of the utmost importance to consult your healthcare provider before changing vitamin supplement regimens.  Especially, in children, or those with kidney or liver disease, or history of kidney stones. But, in the midst of a global pandemic, we should use every low risk tool at our disposal to safely improve our health and immune function.

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