New review makes a compelling case that seasonal lack of the “sunshine vitamin” causes the sharp wintertime rise in flu rates
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 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
*For our full test results, click here.
“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 radicals—i.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."[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.”
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.
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.’”
“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.”
- “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
- “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.”
Stay tuned… we’ll keep you posted on developments regarding vitamin D and human health.
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