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Vitamin D supplementation as a means of preventing respiratory infections has been a source of controversy for decades. As recently as 2016, reviews of research found wide, unexplained discrepancies in research on the vitamin.  

Then in 2017, a large, systematic meta-analysis of controlled Vitamin D studies uncovered the likely source of confusion. Vitamin D, if supplemented daily or weekly can indeed have a significant, even profound effect on immunity to respiratory viruses. The effect is most pronounced among those who are Vitamin D deficient.¹

If supplemented in one-time or sporadic mega-doses (boluses) the powerful effects are not seen.

In other words, it’s not enough just to raise your blood levels of Vitamin D. It matters how you go about it.

D-eficiency?

But how many of us actually are deficient in Vitamin D? If we take the United States as an example, some of the most extensive data available to use comes from 2005-2006 National Health and Nutrition Examination Survey. Of the 4495 participants that they studied, they found the overall rate of vitamin D deficiency was 41.6%, with the highest rate seen in African Americans (82.1%), followed by Hispanics (69.2)2

There are many studies that show that deficiency rates are much higher in wintertime and in regions with less sunlight.3  And that that they are higher still in populations that are living predominantly or exclusively indoors (eg. nursing and extended-care facility residents.)4, 5, 6

The following are some of the populations most prone to Vitamin D deficiency:

  • Breastfed infants, because human milk is a poor source of the nutrient. Breastfed infants should be given a supplement of 400 IU of vitamin D each day.
  • Older adults, because their skin doesn’t make vitamin D when exposed to sunlight as efficiently as when they were young, and their kidneys are less able to convert vitamin D to its active form.
  • People with dark skin, because their skin has less ability to produce vitamin D from the sun.
  • People with disorders such as Crohn’s disease or celiac disease who don’t handle fat properly, because vitamin D needs fat to be absorbed.
  • Obese people, because their body fat binds to some vitamin D and prevents it from getting into the blood.7
  • People who are institutionalized; particularly care-home residents, because they have less access to sunlight.8

What About you?

Do you spend much of your day outdoors where you get a lot of sunlight on your skin? Or are you indoors a lot? Do you live in an open, relatively undeveloped area, or in a city with tall buildings that obstruct the sun? Are you in one of the populations listed above for particular risk of Vitamin D deficiency?

But How Effective?

The giant 2017 meta-analysis of Vitamin D studies found that for those with acute Vitamin D deficiency (less than 10mg/nl) a 70% reduction in respiratory infections occurred with daily or weekly supplementation.9

Those with less acute deficiency, between 10 mg/nl and 30 ng/ml, experienced a roughly 25% reduction.10

And those with levels of 30 ng/ml or higher did not experience a reduction in the incidence of respiratory infections.11

Other studies have found a very sharp drop in the incidence of influenza among specific populations. For example, schoolchildren receiving 1200 i.u. supplementation of Vitamin D daily cut infections by 42%.12

D vs COPD

Vitamin D deficiency is also recognized as a significant factor for increased risk of COPD (Chronic Obstructive Pulmonary Disease) and severe COPD, which are themselves significant co-morbidity factors for respiratory viruses – i.e. they make it much more likely you’ll get seriously ill or worse.13

D vs Depression

Vitamin D deficiency is also a significant factor for increased risk of clinical depression.14

D vs COVID-19

Do the significant and in some cases dramatic protective effects of Vitamin D with respect to many respiratory infections and conditions apply to COVID-19 as well?

Answer: Research is in its early stages, so all findings should be considered preliminary. However, several studies point to a promising correlation between Vitamin D deficiency and COVID-19 health outcomes. The likelihood of becoming symptomatic, severity of symptoms, and mortality all appear to be affected. One rapid response article published in The Biomedical Journal and the British Medical Journal found that the COVID-19 ICU (Intensive Care Unit) risk is 20 times higher in the Vitamin D deficient. Whether the benefits in fact prove to be that significant remains to be seen. As research unfolds, it will be important to remain mindful of the distinction noted above between large bolus doses, which are not typically effective, and daily or weekly supplementation that has demonstrated remarkable efficacy with respect to other respiratory viruses. It should also be noted that daily or weekly supplementation can be provided at extremely low cost, which may not be the case with large bolus regimens that are currently being studied. 15, 16, 17, 18, 19

How Much is Safe?

While Vitamin D supplementation can be a powerful ally in boosting immunity, excessive supplementation can bring health risks. Vitamin D raises calcium levels in the blood, which for many people can be of benefit. But if taken too far, excessive doses can have numerous side effects and potentially lead to serious health consequences, including bone loss, heart disease, and kidney disease as well. 

A recent study looked at data from more than 20,000 people over a 10-year period. Out of those It found that only 37 people had Vitamin D blood levels above 100 ng/ml (250 nmol/l).20

Vitamin D intoxication is thought to occur when blood levels rise above 150 ng/ml (375 nmol/l). Because the vitamin is stored in body fat and released into the bloodstream slowly, the effects of toxicity may last for several months after you stop taking supplements.)21

The National Institute of Health advises that the “daily upper limit for vitamin D is 25 mcg to 38 mcg (1,000 to 1,500 IU) for infants; 63 mcg to 75 mcg (2,500 to 3,000 IU) for children 1-8 years; and 100 mcg (4,000 IU) for children 9 years and older, adults, and pregnant and lactating teens and women.22

Although NIH concludes that in the United States “almost no one has levels that are too high,” it also states that long term intakes above the upper limits “increase the risk of adverse health effects.”23

NIH finds that most reports “suggest a toxicity threshold for vitamin D of 10,000 to 40,000 IU/day and serum 25(OH)D levels of 500–600 nmol/L (200–240 ng/mL). It then goes on to state that “While symptoms of toxicity are unlikely at daily intakes below 10,000 IU/day, the FNB  (Food and Nutrition Board) pointed to emerging science from national survey data, observational studies, and clinical trials suggesting that even lower vitamin D intakes and serum 25(OH)D levels might have adverse health effects over time.)”24 

(Note: NIH also notes that the largest clinical trial for Vitamin D and Cancer (Called VITamin D and OmegA-3 TriaL or “(VITAL)” found that African Americans taking vitamin D had a 23% reduction in cancer incidence.)25

(Note: Vitamin K has been shown to mitigate potential effects of excess Vitamin D. But in some cases it can carry its own risks, particularly for those with kidney or liver disease.26

A 2018 study focused exclusively on potential Vitamin D Toxicity (VDT) (rather than on potential benefits) speculated that there could be theoretical risks associated with moderate supplementation, but the only reliable evidence of negative outcomes was found with massive intravenous bolus doses as high as 500,000 i.u., or with daily supplementation on the order of 200,000  to 300,000 i.u. daily as was regularly practiced in the 1940’s.27

From the study:

The Institute of Medicine (IOM) (15) and the Endocrine Society (14) have both concluded that acute VDT is extremely rare in the literature, that serum 25(OH)D concentrations must exceed 150 ng/ml (375 nmol/l), and that other factors, such as calcium intake, may affect the risk of developing hypercalcemia and VDT. Regardless of additional risk factors for VDT, many studies provided evidence that vitamin D is probably one of the least toxic fat-soluble vitamins, much less toxic than vitamin A (4). Dudenkov et al. (2) researched more than 20,000 serum 25(OH)D measurements performed at the Mayo Clinic from 2002 to 2011 to determine the prevalence of VDT, demonstrated by the presence of hypercalcemia. The number of individuals with a serum 25(OH)D concentration >50 ng/ml (>75 nmol/l) had increased by 20 times during that period. However, relatively high 25(OH)D concentrations coincided with a normal serum calcium concentration.

Only one patient (emphasis added), with a25(OH)D concentration of 364 ng/ml (910 nmol/l), was diagnosed with hypercalcemia.”28 

The authors go on:

“Pietras et al. reported that healthy adults in a clinical setting, receiving 50,000 IU of vitamin D2 once every 2 weeks (equivalent to approximately 3,300 IU/day) for up to 6 years, maintained 25(OH)D concentrations of 40–60 ng/ml (100–150 nmol/l) without any evidence of VDT. Those 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 (150 nmol/l), but without any evidence of toxicity.29

While the extreme rarity of Vitamin D Toxicity is striking, that does not  mean that the potential for toxicity should be ignored, and the authors are quick to make that point:

“Although VDT resulting in hypercalcemia is rare, it can be life-threatening if not promptly identified.” Moreover, that “without medical supervision, caution is advised for people who self-administrate vitamin D at doses higher than recommended for age and body weight.”30

Another key finding here bears repeating: the actual instances of toxicity in Vitamin D supplementation occur with either massive daily doses in the hundreds of thousands, or with massive bolus doses (similarly) in the hundreds of thousands. In other words, not only are large bolus doses far less effective than daily or weekly supplementation; there is also evidence that they may carry greater risk.

Is it possible that frequent supplementation at moderate doses emulates a natural biological process related to the day/night cycle shared by land-based complex organisms? That there is more involved than simply the blood plasma level of Vitamin D? Any answer would of course be merely speculative.

Except…

The Greatest Source of All

There is one source of Vitamin D that is free, can quickly raise Vitamin D blood levels, and in and of itself does not raise levels too high. It also brings numerous benefits that can’t be ascribed to Vitamin D blood levels alone. We are talking, of course, about the sun. 

A growing body of evidence now suggests that there are benefits to moderate sun exposure that include but go beyond serum Vitamin D levels. Levels at which UV exposure should be avoided due to risk of melanoma are being reconsidered, and there is even evidence emerging that a lack of sun exposure can raise the risk of melanoma.

In a Dermato-Endocrinology article titled “The Risks and Benefits of Sun Exposure 2016” a group of Epidemiologists and Endocrinologists concludes that “Vitamin D supplements are not an effective substitute for adequate sun exposure” and that “the message of sun avoidance must be changed to acceptance of non-burning sun exposure sufficient to achieve serum 25(OH)D concentration of 30 ng/mL or higher in the sunny season and the general benefits of UV exposure beyond those of vitamin D.”31

The authors go on to make several key points:

Sun and Melanoma

“The relationship between melanoma and UVR is 2-sided: non-burning sun exposure is associated with a reduced risk of melanoma, while sunburns are associated with a doubling of the risk of melanoma. It has long been observed that outdoor workers have a lower incidence of melanoma than indoor workers. A 1997 meta-analysis found an OR of 0.86 (95% CI: 0.77–0.96) for occupational sun exposure.32

….The public health messages of the past 50 y to avoid sun exposure and to use chemical sunscreens may have contributed to the rise in melanoma incidence.”33

Other Serious Health Conditions

Best remedied by sun exposure when possible, Vitamin D deficiency is associated with the following serious health conditions:34

  • Several forms of cancer
  • Cardiovascular disease
  • Liver Disease
  • Multiple Sclerosis
  • Type I Diabetes
  • Rheumatoid Arthritis
  • Macular Degeneration
  • Alzheimers and cognitive decline
  • Obesity 

Mortality

“Lindqvist et al. 2014 assessed the avoidance of sun exposure as a risk factor for all-cause mortality for 29,518 Swedish women in a prospective 20-year follow-up of the Melanoma In Southern Sweden cohort and found that the population attributable risk for all-cause mortality for those habitually avoiding sun exposure was 3%. As compared to the highest sun exposure group, the all-cause mortality rate was doubled (RR 2.0, 95% CI 1.6–2.5) among avoiders of sun exposure and increased by 40% (RR 1.4, 95% CI 1.1–1.7) in those with moderate exposure.

…avoidance of sun exposure is a risk factor for death of a similar magnitude as smoking. Our finding that avoidance of sun exposure was a risk factor for all-cause death of the same magnitude as smoking is novel.”35 

Sun Strategies

The exact level of sun exposure that’s optimal to achieve health benefits while avoiding risks is likely to be a subject of controversy for some time. But there are specific ways to potentially increase benefits and reduce risks.

These include:

  • Getting sun just shy of the point at which you would burn. There should be no pain on the skin, and at most a very slight change in color.36
  • Covering parts of the body that are sun damaged, prone to burning, or have had the most severe sunburn in the childhood years, and allowing full sun on other parts of the body to achieve exposure just short of the point of sunburn.)
  • Getting sun more toward mid-day rather than later in the afternoon. There is evidence that this may raise Vitamin D levels more effectively, and also present lesser risk.37, 38  

Note: If despite your best efforts at prevention you become ill with a serious respiratory virus, that may be a time to consider temporarily discontinuing Vitamin D supplementation until you have recovered. Concerns have been raised that Vitamin D may increase what are known as “inflammatory cytokines,” potentially setting off a “cytokine storm” that can lead to Acute Respiratory Distress Syndrome (ARDS) — the often fatal condition that can develop with serious respiratory infections. There is considerable evidence that Vitamin D actually reduces inflammatory cytokines, but not enough is known to draw conclusions, so there is reason for caution.39, 40, 41  In general, however, Vitamin D deficiency is strongly implicated in ARDS. 42 

What to Do? 

So how much should you get out in the sun? If you do supplement, how much should you take? As we’ve seen, some factors you may want to consider are how much sunshine you get on your skin daily, whether you’re fair-skinned (need less) or dark-skinned (need more) and whether you’re in one or more of the groups listed above that have greater risk for Vitamin D deficiency. You may also consider supplementing more during the winter and less during the summer, or perhaps more on days when you don’t get sun, and less on days when you do.

For those choosing to take a relatively higher Vitamin D dose for an extended period of time, a blood test of your Vitamin D level and consultation with your physician or other qualified health care provider after a few weeks may give you some clarity about your Vitamin D levels, and whether supplementation has gone too far.

It is ultimately your health, and your choice. You now have some of the latest information with which to make your decision.

Medical Disclaimer: All information, material and content of this website is for informational purposes only, and are not intended to be, should not be interpreted as, or used as a substitute for, the consultation, diagnosis, advice and/or medical treatment of a qualified physician or healthcare provider, nor as recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action.

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