Vitamin D: Immune-Booster, Cancer & COVID-Fighter, Bone-Builder & Sleep-Aid


To date there are 28 essential micronutrients- 14 vitamins and 14 minerals. The minerals can further be broken down into major minerals (the 6 electrolytes) and trace minerals (of which there are 8), whereas vitamins can further be broken down into water soluble vitamins (the 8 B vitamins, along with choline and vitamin C) and fat soluble vitamins (A, D, E & K). These 28 nutrients are called essential because 1) the body cannot produce them on its own and 2) a deficiency in these nutrients, over time, has been shown to cause disease. Today we're taking a closer look at vitamin D.


Vitamin D is a micronutrient that gets a relatively good bit of attention, and rightly so. Vitamin D is an essential fat soluble vitamin that’s unique in that it often acts more like a hormone than a vitamin in the body. Vitamin D3 plays a major role skeletal (bones and teeth), immune system and endocrine (hormone) health, and a somewhat more minor role in cardiovascular and neurological health (vitamin D2 is another, less effective, form of vitamin D and ideally should be avoided).

Deficiencies in vitamin D have been linked to several diseases, including sleep disorders, thyroid diseases, bone diseases (including rickets, osteomalacia and osteoporosis), diabetes, chronic pain, autoimmune diseases, cardiovascular disease, Alzheimer’s, dementia and serious gastrointestinal diseases like Crohn’s and ulcerative colitis, as well as 17 different types of cancer. [1-2]


The COVID-19 coronavirus pandemic hit the world in March of 2020, and as of February 18, 2021 over 110 million cases and 2.45 million deaths related to COVID have been reported. While risk factors like old age, obesity, cardiovascular disease, diabetes and lung disease are now well established, a growing mountain of emerging research is showing low vitamin D status to be yet another risk factor for COVID-19. Low levels of vitamin D are associated with bacterial and viral infections, and studies have shown that countries with lower average levels of 25-hydroxyvitamin D (the major circulating form of vitamin D in the body) have a higher COVID-19 mortality rate. At least 14 observational studies have reported inverse correlations between vitamin D concentrations in the blood and COVID-19 incidence, severity and death. [3-9]


Several studies suggest that vitamin D deficiency is rampant in the United States, such as a 2018 study from the Cureus Journal of Medical Science that looked at data from nearly 5000 American adults and found that more than 40% were deficient in vitamin D, including more than 80% African Americans and more than 60% of Hispanic Americans. [10]



Why is this the case? For starters, very few foods naturally contain vitamin D. The top 2 food sources are salmon and eggs. The Recommended Daily Allowance (RDA) for vitamin D is 400 to 800 IU a day, and a 4oz serving of salmon only contains around 400 IU, and 3 eggs only contain around 125 IU. So it’s extremely difficult to obtain adequate amounts of vitamin D from food alone. [11]


The other 2 options are sunlight and supplements. Although vitamin D is a relatively cheap supplement, the majority of Americans still don’t consume it on a regular basis. Data from 2011 found that only 21% of Americans regularly consume a vitamin D supplement, although data from recent years suggest that number is increasing. [12-13]



With sunshine, the further away from the equator we get, the more difficult it generally is to obtain adequate vitamin D from the sun. The risk of vitamin D deficiency is higher for those living above the 37th parallel, and a large percentage of Americans live north of this line of latitude. [14]

Also, it’s important to know that a few conditions must be met for the body to produce vitamin D from sunshine. For starters, the sun generally needs to be above 50 degrees on the horizon, otherwise the atmosphere tends to block the UVB rays needed for vitamin D production. This is why it’s generally impossible to get vitamin D from the sun in winter months, regardless of how warm or sunny it is. Also, thick cloud cover, most clothing and sunscreen can also block UVB rays from reaching the skin. There are even certain liver and kidney conditions that can also interfere with the body’s ability to produce the metabolically active form of vitamin D (see image below).

Some studies have also shown that the elderly are at an increased risk of deficiency, due in part to their body’s reduced ability to convert vitamin D into its most useful metabolic form. [15-16]



Why is vitamin D deficiency so prevalent in America? Several factors play a role, including...

* Most still don’t regularly consume a vitamin D supplement.

* Many Americans live in northern climates where getting vitamin D from the sun is nearly impossible for many months out of the year.

* As a society we spend more time indoors than we used to.

* We’ve been conditioned for several decades now to cover up with clothing or wear high SPF sunscreen if we’re going to be exposed to the sun.

* And then there’s the widespread prevalence of kidney and liver diseases, both of which are among the top 15 causes of death for Americans.

* And finally there’s an increasing percentage of the population who are elderly. For instance, in 1920 less than 5% of Americans were over 65; today that number is over 15%. [17]

In short, vitamin D is an incredibly important nutrient, but a large percentage of U.S. adults are deficient.


That really depends on the adult and their current vitamin D levels. The first step for many is to get tested.

The current gold standard test is the 25-Hydroxy Vitamin D Blood Test. This test is relatively cheap and is almost always covered by insurance. The test results are either given in nanograms per milliliter (ng/ml) or nanomoles per liter (nmol/L). I usually discuss vitamin D levels using ng/ml, and there are conversion calculators online if you need to convert nanomoles per liter to nanograms per milliliter.

In 2010, the Institute of Medicine (now known as the National Academy of Sciences) set the vitamin D deficiency threshold at 20 ng/ml. A year later, the Endocrine Society set their vitamin D deficiency threshold at 30 ng/ml. To make matters more complicated, we also have other influential organizations like the GrassrootsHealth Nutrient Research Institute, as well as The Vitamin D Society of Canada, which recommend levels in the 40-60 ng/ml range. While some independent researchers suggest that optimal vitamin D levels go as high as 100 ng/ml, many advocate for levels in the 40-80 ng/ml range. This is the range I recommend as well. [18-20]

Several studies back this up, such as one from 2012 that found that vitamin D levels in the 60-80 ng/ml range were most effective for treating 1500 patients with sleep disorders. [21]


So if 40 ng/ml is the minimum threshold to reach, how much daily vitamin D do we need to reach it? Well, The National Academy of Sciences (formerly the IOM) says 400-800 IU is the RDA and 4,000 IU a day is the tolerable upper limit for adults. The Endocrine Society says 1500-2000 IU is the RDA and 10,000 IU a day is the tolerable upper limit.

A 2011 study in the journal Anticancer Research found that “The supplemental dose ensuring that 97.5% of the population achieved a vitamin D serum level of at least 40 ng/ml was 9600 IU per day.” [22]

It is for reasons like these that I often recommend adults supplement with a minimum of 5,000-10,000 IU a day of vitamin D3, while having their blood vitamin D levels checked on a regular basis. In other words, many of these scientific findings suggest that the IOM significantly low-balls the amount of vitamin D needed for optimal health.


But what about toxicity concerns with higher dose vitamin D protocols? Several studies have shown that, while 25 hydroxy vitamin D readings in the 90-150 ng/ml range are likely excessive, true vitamin D toxicity isn’t clinically defined until blood serum levels go above 150 ng/ml, and for this to happen a minimum of 40,000 IU a day needs to be taken for several months. [23-26]



The research seems split here. Some research suggests that supplemental vitamin D is better at improving serum D levels, while other research seems to show that sunshine does a better job at raising levels in the body. [27-28]

While I am a big fan of people regularly getting exposure to sunshine, I’d offer 2 cautions- one, you want to avoid getting sunburned as much as possible (no brainer, right?). A zinc oxide-based sunscreen is a safer option if you’re going to be exposed for longer periods of time. And two, if your skin isn’t healthy or you’ve had skin cancer or are at a higher risk of developing skin cancer, you might opt for taking supplemental vitamin D, even when you can get vitamin D from the sun. [29-30]


In my opinion the best vitamin D supplements are those derived from fish. BlueBonnet is one of the few companies that make such a product. The vast majority of D supplements come from lanolin, which is produced by sheep. Most people will do fine with lanolin-derived vitamin D products but those who are more sensitive may develop a skin allergy. There are vegan vitamin D supplements available as well, such as those derived from lichen, which is a composite of fungus and algae.


If you’re going to take higher doses of supplemental vitamin D or you’re going to be exposed to vitamin D-producing sunshine on a regular basis, you should consider taking a vitamin K2 supplement.

As some might know, vitamin D significantly increases calcium absorption, and vitamin K2 helps direct that calcium into the bones where the vast majority of it belongs. Too much calcium in the soft tissues has been linked to cardiovascular disease, kidney stones and hormonal disorders. [31-36]


  • Vitamin D is an important essential nutrient whose deficiency has been linked to several common disease conditions.

  • More than 40% of Americans are deficient in vitamin D, and the numbers for Hispanic and African Americans are much higher than that.

  • Not many foods contain notable amounts of vitamin D.

  • Several factors play a role in why vitamin D deficiency is so prevalent in the U.S.

  • The 25-Hydroxy Vitamin D blood test is a commonly run test and is helpful in identifying deficiency, sufficiency and toxicity.

  • Studies suggest that vitamin D test results of 40-60 ng/ml is ideal for optimal health, and 60-90 ng/ml may be therapeutic for those dealing with certain acute and serious conditions.

  • Vitamin D derived from fish oil tends to be highly bioactive while also having low allergen potential.

  • Studies are split on whether sunshine or supplementation is most effective at raising 25-hydroxy vitamin D levels.

  • Vitamin D increases calcium absorption (and calcium levels in the blood), and Vitamin K2 plays an important role in regulating healthy blood and bone calcium levels.


If you're ready for a significant, positive health change and want to take a holistic, personalized, evidence-based approach to get there, let me know! I provide health and nutritional consulting as well as personal training services to both local (Charleston, SC area) and remote clients. Email me at to find out more today.


1 (May 2020 StatPearls on Vitamin D)

2 (2006; review suggesting avoidance of vitamin D2 in favor of vitamin D3)

3 (Jan 2021; Patients Hospitalized With COVID-19 Shown to Have Low Levels of 25-Hydroxyvitamin D; low levels are associated with bacterial and viral infections; countries with lower mean levels of 25-hydroxyvitamin D have a higher COVID-19 mortality rate; study looked at 330 hospitalized COVID patients from Armenia)

4 (Jan 2021; another article on the study of 330 Armenian COVID patients)

5 (Jan 2021; “Another recently recognized potential risk factor is vitamin D deficiency. Vitamin D is an important modulator of innate and acquired immunity. Low levels are associated with bacterial and viral infections… in countries with lower mean levels of 25-hydroxyvitamin D, mortality from COVID-19 is higher. Preliminary studies suggest that vitamin D supplementation may improve outcomes… recent reports have shown markedly reduced levels of 25-hydroxyvitamin D among those hospitalized with COVID-19”)

6 (Dec. 2020; “higher serum 25(OH)D concentrations are associated with the reduced risk and severity of COVID-19” with “the strongest evidence to date (coming) from 14 observational studies that report inverse correlations between serum 25(OH)D concentrations and SARS-CoV-2 positivity and/or COVID-19 incidence, severity and/or death.”)

7 (Dec 2020 study of 30 Greek COVID patients; “the low vitamin D group had an increased risk of 28-day mortality… low 25(OH)D levels may predispose COVID-19 patients to an increased 28-day mortality risk”)

8 (Dec. 2020; “Evidence linking vitamin D deficiency with COVID-19 severity is circumstantial but considerable”… study authors suggest 800-4000 IU/day)

9 (Sept 2020 study of 235 hospitalized patients found that “Hospitalized COVID-19 patients who were vitamin D sufficient, with a blood level of at least 30 ng/mL had a significant decreased risk for adverse clinical outcomes including becoming unconscious, hypoxia and death. In addition, they had lower blood levels of an inflammatory marker (C-reactive protein) and higher blood levels of lymphocytes (a type of immune cell to help fight infection)… This study provides direct evidence that vitamin D sufficiency can reduce the complications, including the cytokine storm and ultimately death from COVID-19”)

10 (2018 study looking at NHANES data from 2012; found >40% of total population, with >60% Hispanics & >80% African Americans deficient)


12 (2014; nutritional supplement use data from 2007-2011, compiled by The Council for Responsible Nutrition (CRN))


14 (2010 article; “Populations living at a latitude higher than 37° north of the equator in the Northern Hemisphere are at the greatest risk of developing vitamin D deficiency. In the United States, this translates roughly to a line drawn between San Francisco and Richmond, Virginia.”


16 (April 2020 StatPearls on Vitamin D Deficiency)

17 (data on the elderly 65+ in the U.S., 1900-2050)

18 (2012 review highlighting differences between IOM’s baseline for vit D deficiency [20 ng/ml] and Endocrine Society’s [30 ng/ml])

19 (2011 article outlining Endocrine Society’s rationale for recommending >30 ng/ml as baseline for deficiency)


21 (2012; sleep disorders linked to vit D deficiency; 25(OH) vitamin D3 blood levels of 60-80 ng/ml needed for optimal sleep [notably higher than the 20-30 ng/ml baseline])

22 (2011 study showing 9600 IU/day needed for 97.5% of population to go >40 ng/ml)

23 (2018; case reports on vitamin D toxicity)

24 (2018 review on vitamin D toxicity; “…findings were consistent with the observation by Ekwaru et al. that Canadian adults who ingested up to 20,000 IU of vitamin D3 per day had a significant increase of 25(OH)D concentrations, up to 60 ng/ml, but without any evidence of toxicity.”)

25 (2013 review on vitamin D deficiency, sufficiency & toxicity; 90-150 ng/ml = excessive and >150 ng/ml = toxicity; 90 ng/ml is highest recorded reading through sunshine alone (no supplementation); “Vieth reported that vitamin D toxicity probably begins to occur after chronic consumption of approximately 40,000 IU/day”)

26 (2017; in case studies of 3 adult males, doses of 10k-60k IU/day for 2-6 yrs safely tolerated)

27 (2017; rat study showing sunshine more effective than supplementation at improving serum vitamin D levels)

28 (2011 study showing supplementation more effective than sunshine at improving serum vitamin D levels)

29 (2019 study on safety of zinc oxide as a sunscreen)

30 (2017 study on safety of zinc oxide as a sunscreen)

31 (2020; The combination of vitamin K and D can significantly increase the total bone mineral density and significantly decrease undercarboxylated osteocalcin, and a more favorable effect is expected when vitamin K2 is used.”)

32 (2019; “We propose therapeutic strategies with vitamin K2 treatment to prevent or hold progression of vascular calcification as a consequence of excessive calcium intake…supplementation of calcium—either with or without vitamin D—comes at the price of increased risk of vascular calcification. Clinical studies demonstrate that increased intake of vitamin K could be a promising complementary nutrient in supporting both bone health and protecting vascular calcification.”)

33 (2019; dangers of calcium supp for osteoporosis can increase CVD & CKD risk; points to need for vit K2 supp w/ calcium)

34 (2017; Vitamin K2 may be a useful adjunct for the treatment of osteoporosis, along with vitamin D and calcium, rivaling bisphosphonate therapy without toxicity. It may also significantly reduce morbidity and mortality in cardiovascular health by reducing vascular calcification.”)

35 (2017; Current evidence supports the notion that joint supplementation of vitamins D and K might be more effective than the consumption of either alone for bone and cardiovascular healthvitamin D and calcium supplementation along with vitamin K deficiency might also induce long-term soft tissue calcification and CVD”)

36 (2015; “Vitamin K2 promotes arterial flexibility by preventing accumulation of arterial calcium, and supplementation with it could correct calcium amounts in the body that are out of balance. Thus, calcium in tandem with vitamin K2 may well be the solution for bringing necessary bone benefits while circumventing an increased risk for heart disease”)