Last week, Vital Choice Founder Randy Hartnell heard a plea from Commander John C. Umhau, MD, MPH, CPE, with whom we've previously corresponded.
Dr. Umhau — who recently retired from the United States Public Health Service (USPHS) — co-authored a 2006 review of the then-available cevidence concerning vitamin D and respiratory infections. 
He and his colleagues made a compelling case that wintertime’s low seasonal blood levels of vitamin D explain — to a significant extent — why rates of flu rise during its dimmer days and recede when days grow sunnier in spring.
In Dr. Umhau's message, he urged Randy to share that research, and the supportive findings of a 2017 evidence review, which appear comparably relevant to the COVID-19 coronavirus crisis: 

“As a recently retired Commander in the USPHS, I feel responsible to share my scientific knowledge about a critical opportunity to prevent COVID-19 that's  overlooked by the government. While serving as a senior clinical investigator at NIH, I authored a paper with a number of experts which outlined evidence that respiratory infections such as epidemic influenza are driven by vitamin D deficiency.

“Our paper led to many studies, which, as noted in the British Medical Journal Review of 2017, indicated that vitamin D supplementation was protective against acute respiratory tract infection such as COVID-19. As of today, this research has not stimulated the appropriate national response to this issue.”

Commander John C. Umhau MD, MPH, CPE
United States Public Health Service (USPHS), Retired
Below, you'll see the December, 2006 Vital Choices newsletter article — titled "Vitamin D Likely Fights Lung-Focused Viral Villains" — in which we summarized his team's landmark evidence review concerning vitamin D and respiratory infections.
As well as the sun-related reason proposed by Dr. Umhau and his colleagues — less internal production of vitamin D due to shorter days and weaker wintertime sunrays — there are some other possible contributors to the seasonal nature of the flu:
  • Viruses survive longer on surfaces when the air is colder.
  • Winter keeps people indoors, so they interact closely more often.
  • Viruses are damaged by ultraviolet (UV) sunrays, which are weaker during the winter.
  • Cold air dries out mucous membranes in the nose, eyes, and throat, which impairs the body’s ability to shed invading viruses via sneezes, coughs, and tears.
  • Schools are full of children from fall through spring but empty out in the summer — and when they interact closely in school, children become major transmitters of cold, flu, and other viruses.
Before we review the compelling 2006 paper on vitamin D and the flu by Dr. Umhau and his colleagues, let's review some recent findings, including the supportive conclusions of the 2017 British Medical Journal (BMJ) clinical-evidence review that Dr. Umhau cited in his message to Randy.
Vitamin D vs. viral lung infections: An overview
This hormone-like nutrient is an essential part of the body’s “innate” immune system — our first line of defense against pathogenic viruses and microbes — and helps the body identify and kill microbial invaders, including viruses: see Vitamin D Activates Two Key Immune Systems.

Vitamin D is an especially important ally in the lungs, which flu and coronaviruses — including COVID-19 — tend to attack. Epidemiological and clinical studies suggest that higher blood levels of vitamin D help prevent respiratory infections, as we reported in Vitamin D Cuts Flu Rate in First Clinical Trial, Flu and Colds Risk Linked to Vitamin D Lack, Vitamin D Lack Linked to Kids' Flu and Colds Risk, and Vitamin D Bolsters Lung Defenses.

Stormy echoes of the
1918 "Spanish" flu pandemic

The 1918 flu — which likely came from chickens or other birds — first appeared among soldiers at Fort Riley, Kansas.
They carried the virus on their way to Europe during World War I, and back again, which led Americans to mistakenly — but perhaps conveniently — calling it the Spanish flu.
Ironically, greater percentages of children and the elderly survived the deadly 1918 "Spanish" flu pandemic, probably because their immune systems — which were respectively immature and age-weakened — couldn't mount a counterproductive cytokine storm, or only relatively weak, survivable storms, and/or because they'd previously been exposed and acquired resistance to a similar virus.
Conversely, the 1918 flu pandemic killed higher proportions of younger, healthy people than do typical flu viruses, because the cytokine storm unleashed by their robust immune systems caused raging inflammation and filled their lungs with fluid.
Most importantly, a 2017 clinical-evidence review in the British Medical Journal (BMJ) — which covered 25 trials involving 11,321 participants of all ages — found that supplemental vitamin D reduced the risk for respiratory infections, especially among people with low vitamin D levels. As the authors wrote, “Vitamin D supplementation … protected against acute respiratory tract infection overall.” (Martineau AR et al. 2017)

The authors of that BMJ evidence review also confirmed that vitamin D can help curb the potentially deadly “cytokine storm” immune-system overreaction that triggers wildly excessive inflammation and fills a patient’s lungs with fluid: see Vitamin D Lack May Promote Sickening Inflammation.

Cytokine storms have apparently killed some young-adult COVID-19 patients and they definitely killed some patients afflicted by the recent, closely related SARS and MERS coronavirus epidemics (Cameron MJ et al. 2007; Liu L et al. 2019; Mehta P et al. 2020).  
We should note that omega-3 DHA and EPA are essential to the body's ability to make the messenger chemicals it uses to end or "resolve" inflammation, called special pro-resolving mediators or SPMs. 
Given these seafood-source omega-3's critical importance to healthy inflammation control, it makes sense to include ample amounts of fatty fish and/or fish oil in your diet. (The body can make small amounts of omega-3 EPA from the omega-3 ALA fat found in in certain plant foods — but it can’t use ALA to end inflammation.)
Note: Supplemental vitamin D may or may not help prevent or ease the common cold, and that may depend in part on a person's blood levels — people with lower levels may benefit from raising dietary intake from seafood or supplements, and/or getting more sun. As it happens, only one in five "colds" — a term that covers any relatively mild, non-flu, viral respiratory infection — are caused by a coronavirus. For more than that, see Friendly Bugs Cut Colds; Vitamin D Defeated.

Originally published December 2006
Vitamin D Likely Fights Lung-Focused Viral Villains
Evidence review made a compelling case that lack of the “sunshine vitamin” enables the flu — and other lung-focused viruses
A compelling scientific paper offers a persuasive explanation for the generally seasonal nature of the flu.
Influenza infections sweep the Northern Hemisphere during the winter months and usually peak in America, Canada, and Europe between late December and March.
None of the numerous theories floated to explain the seasonal flu spike — from the flood of frigid air to the wintertime tendency of people to huddle indoors — fully passes the scientific-credibility test.

Key Points

  • Evidence review found much evidence that flu arises in winter due at least in part to seasonal deficiencies of vitamin D.
  • The CDC agrees that conventional explanations for the seasonal nature of flu don't fully account for it.
  • Harvard Public Health head called for higher vitamin D intake; cited fish as leading source.
Dr. Scott Dowell is director of the Global Disease Protection Program at the Centers for Disease Control and Prevention. In a recent interview in LOHAS journal he called the conventional explanations “… astonishingly superficial and full of inconsistencies.”
Dr. Dowell and others find merit in a provocative new hypothesis: one that attributes the winter-focused nature of flu epidemics in the northern third of the globe to the season's obvious shortage of vitamin-D-generating sunshine.
Why would vitamin D help protect against the flu? It plays a key role in the body's immune-system defense against infection, especially in the lungs, where flu and corona viruses tend to settle.
Influenza kills an average 36,000 people in the U.S. every winter. As Dowell said, should the new hypothesis prove true, “…the potential impact would be far greater than the current influenza vaccine.”
Paper's authors offer radically different view of the flu
The authors of the new [2006] evidence review included leading vitamin D researchers Michael C. Holick of Boston University and Edward Giovanucci of Harvard University, as well as Commander John C. Umhau, MD, MPH, CPE of the United States Public Health Service
Many mysteries surround the seasonal nature of influenza, and the simultaneous occurrence of local epidemics in widely separate regions: characteristics that make it hard to explain influenza epidemics as typical person-to-person viral infections, like the common cold or measles.
The study's authors make a strong case that the mystery factor behind the seasonal rise in flu rates in the winter is a lack of sunshine-generated vitamin D.
If they're right, high doses of supplemental vitamin D could provide a safe, effective, natural remedy for garden variety flu, and could even help prevent and treat far more dangerous forms, such as the flu virus that killed an estimated 50-100 million people worldwide in 1918.

Fish fit the vitamin D bill; Sockeye salmon stand out

Certain fish rank among the very few substantial food sources of vitamin D.
Among fish, wild sockeye salmon may be the richest vitamin D source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:

Vitamin D per 3.5 ounce serving

Sockeye salmon  687 IU

Albacore tuna  544 IU

Silver salmon  430 IU

King salmon  236 IU

Sardines  222 IU

Sablefish  169 IU

Halibut  162 IU

The new hypothesis holds that the various flu viruses lie dormant in people and emerge during the dimmer days of winter in northerly climes and during the rainy seasons in tropical regions: especially in people whose darker skin color — or sun avoidance or heavy sunscreen use — leaves them very low in vitamin D.
For example, studies ranging from Malaysia and South India to China and Japan show that women there have surprisingly low levels of vitamin D, especially in their winter months.
Researchers attribute the lack of vitamin D in these Asian nations in part to women's indoor careers and a cultural preference for pale skin that leads them to use clothes, parasols, and sunscreens to avoid tanning. (This unhealthful prejudice is common among East and South Asian women, where skin-lightening creams are increasingly popular.)
The US recommended daily allowance (RDA) for vitamin D is 400 international units (IU) — and on sunny days, a fair-skinned person generates the equivalent of 20,000 international units (IU) in just 15-20 minutes. In contrast, one cup of fortified milk contains fewer than 100 IU.
Most vitamin D researchers agree that people should take at least 1,000 IU per day, rather than the US RDA of only 400 IU.  [Editor's Note: Since we published the original article in 2006, the RDA for vitamin D from early childhood through old age has been raised to 600 IUs.] And most experts urge older, heavier, and dark-skinned people — who make and absorb less vitamin D — to take 3-5,000 IU every day.
Excerpts from “Epidemic influenza and vitamin D”
The following quotes come directly from the authors' summary of their findings and conclusions. (We've added some clarifications in brackets [ ].) Note: E.R. Hope-Simpson, M.D. is the British doctor who conducted pioneering research that undermined conventional wisdom concerning the causes of flu outbreaks:
  • “In 1981, R. Edgar Hope-Simpson proposed that a 'seasonal stimulus' intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. … We conclude that vitamin D, or lack of it, may be Hope-Simpson's ‘seasonal stimulus'.”
  • “Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D… a steroid hormone, has profound effects on human immunity.”
  • “[vitamin D] acts as an immune system modulator, preventing excessive expression of inflammatory cytokines [messenger proteins released by immune-system cells] and increasing the ‘oxidative burst' potential of macrophages.” [Macrophages are immune system cells that spew oxygen free radicalsi.e., an “oxidative burst”— intended to kill invading bacteria and viruses].”
  • “Perhaps most importantly, it [vitamin D] dramatically stimulates the expression of potent anti-microbial peptides, which exist in [immune system cells called] neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection.”
  • “Volunteers inoculated with live attenuated [weakened] influenza virus are more likely to develop fever and serological [blood-test] evidence of an immune response in the winter." [Editor's Note: In other words, the dimmer sunlight and consequent low vitamin D levels in winter months allow flu viruses to infect cells in significant numbers, and this causes the body to mount an immune response. But in the summer, blood levels of vitamin D rise, which allows the body to produce enough anti-microbial peptides to cripple the ability of influenza virus to infect significant numbers of cells, thereby reducing or eliminating the body's need to mount a major, cytokine-mediated, inflammatory immune response to the virus.]
  • “Vitamin D deficiency predisposes children to respiratory infections.”
  • “Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D).”
  • “An interventional study [clinical trial] showed that vitamin D reduces the incidence of respiratory infections in children.”
British country doctor challenged conventional wisdom
Dr. John J. Cannell, one of the authors of the provocative new review, highlighted the pioneering work of Dr. Hope-Simpson in a recent edition of his vitamin D newsletter.
Hope-Simpson, who died in 2003 at the age of 95, marshaled his maverick research on influenza in a 1992 book titled “The Transmission of Epidemic Influenza.”

In his essay, Dr. Cannell summarized some of Dr. Hope-Simpson's cogent but inconvenient observations as follows (key points underlined for emphasis):

  • “Going back to 1945, he discovered that influenza epidemics above 30 degrees latitude in both hemispheres occurred during the six months of least solar radiation. Outbreaks in the tropics almost always occur during the rainy season.”
  • “Hope-Simpson concluded, ‘Latitude alone broadly determines the timing of the epidemics in the annual cycle, a relationship that suggests a rather direct effect of some component of solar radiation acting positively or negatively upon the virus, the humans host or their interaction.'”
  • “Hope-Simpson rejected the theory that this year's virus is only transmitted from actively infected persons to well persons, concluding instead the facts were more consistent with transmission by symptom-less carriers who become contagious when the sun is either in the other hemisphere or obscured by the rainy season.”
  • “He theorized that annual movement of the sun caused a ‘seasonal stimulus that reactivates latent virus in the innumerable carriers who are everywhere present, so creating the opportunity for epidemics to occur in the wake of its passage.'”
We'll have to await the results of controlled clinical studies to know whether vitamin D really fights the flu.
But leading vitamin D researchers believe that it makes good sense to take ample daily doses of vitamin D (i.e., 2-4,000 IU) to help prevent cancer and osteoporosis, and the authors of the new paper say it can't hurt to start taking take larger doses temporarily if you feel a flu coming on.
While vitamin D can be toxic if taken in very large doses over a period of weeks or months, all of the available evidence indicates that it is safe to take daily doses that are at least several times higher than the US government's established safe upper level dose (Vieth 1999, 2001, 2006).
The official US safe maximum intakes of vitamin D are 1,000 to 1,500 IU/day for infants, 2,500 to 3,000 IU/day for children aged 1-8 years, and 4,000 IU/day for children aged nine years and older, adults, and pregnant and lactating teens and women.
Authors propose preventive and therapeutic use of vitamin D
In their new paper, some of American's preeminent vitamin D researchers went beyond hypothesizing to recommend prudent anti-flu use of vitamin D.
Dr. Cannell noted the hypothetical nature of his team's findings, saying “Like all theories, our theory must withstand attempts to be disproved with dispassionately conducted and well-controlled scientific experiments.”
But their research certainly suggests the possibility of some immediate practical implications:
  • “physiological [i.e., maintenance] doses of vitamin D (5,000 IU a day) may prevent colds and the flu…”
  • “physicians might find pharmacological [i.e., therapeutic] doses of vitamin D (2,000 IU per kilogram of body weight per day for three days) useful…”
  • “We recommend that enough vitamin D be taken daily to maintain 25-hydroxy vitamin D levels at levels normally achieved through summertime sun exposure (50 ng/ml). For many persons, such as African Americans and the elderly, this will require up to 5,000 IU daily in the winter and less, or none, in the summer, depending on summertime sun exposure.”
Newsweek provides forum for vitamin D pitch
Meir Stampfer, M.D., chair of the epidemiology department at the Harvard School of Public Health, wrote a column in last week's [2006] issue of Newsweek magazine, in which he decried the vitamin D deficiencies common among Americans.
These were some of his arguments for raising the public profile of vitamin D, to ensure that Americans to get much more of it via foods and supplements:
  • “If applied adequately to protect against sun-induced skin damage and to reduce the risk of skin cancer, sunscreen lowers the skin's ability to form vitamin D by more than 95 percent. More of us are older and fatter; age and obesity also reduce the amount of vitamin D we produce. An average 70-year-old can produce only about a quarter of the vitamin D of a 20-year-old. Obese people generally have substantially lower blood levels of vitamin D.”
  • “…in Boston between November and March, the ultraviolet radiation from the sun is insufficient to produce vitamin D, even with abundant skin exposure on a sunny day. The farther you go away from the equator, the greater the effect. One study found that among white girls in Maine, 48 percent had low vitamin D blood levels at the end of the winter, while only 17 percent were deficient at the end of the summer. Clothing can play a big role as well.
  • “Skin pigmentation also affects the way we process vitamin D.… Indeed, the majority of African-Americans have low levels of vitamin D.
  • “Finding ways to counteract these barriers to getting enough vitamin D is the next challenge. … The only foods with high levels of vitamin D are fatty fish and certain kinds of mushrooms.”
  • “Among nutritionists working on vitamin D, there is general agreement that the current recommended intake of 400 IU per day (600 for those over the age of 70) is too low, and should be re-evaluated. Most believe that 1,000 IU per day would be a reasonable dose for a typical adult in the United States, and I agree. The current official upper limit is 2,000 IU, although many experts think this is too low and should be raised, perhaps to 4,000 IU.” [Editor's Note: Since this paper appeared, the US RDA has been raised to 600 IU for children and adults.]

To view all of our vitamin D articles, search our website for “vitamin D”. And stay tuned … we'll keep you posted on developments regarding vitamin D and human health.



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