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Life Extension Magazine

LE Magazine February 2007

Unraveling a Centuries-Old Mystery

Why Is Flu Risk So Much Higher in the Winter?
By Dale Kiefer

This age-old mystery has confounded scientists for the last century. Like clockwork, influenza infects the majority of its victims during the winter months in both the Northern and Southern hemispheres. Infection with the flu virus leaves millions around the world bedridden with debilitating symptoms such as fever, body pains, sore throat, and cough. The very young and elderly are particularly susceptible to catastrophic complications from the flu, including death. Moreover, the recent emergence of flu strains such as H5N1 leaves many experts on infectious disease worried about the potential for global devastation even worse than that of the 1918-19 flu pandemic, which was linked to at least 50 million deaths worldwide.

A fascinating new theory seeks to explain why flu takes hold during the winter months and why it infects so many people, particularly elderly adults. At the heart of this theory is the presence of a vitamin deficiency in certain populations, including aging adults, around the world.

In this article, we examine this intriguing theory, and how defending against the flu may be as simple as taking enough of a common nutritional supplement.

Influenza Outbreak: A Modern Mystery

One of the greatest medical mysteries of the ages may finally have been solved, thanks to a newly published theory regarding the relationship between influenza and its peak onset during the winter months.1 Published just months before the start of the annual flu season, this novel theory addresses questions that have puzzled scientists for decades: why does flu strike almost exclusively in winter, and why are the elderly often at greatest risk of contracting the disease?

Avian Flu Virus (H5N1)

The answers to these questions are of more than academic interest. In the US alone, influenza hospitalizes more than 100,000 people—and kills more than 30,000—in an average year.2,3 With the recent scares over avian (bird) flu and severe acute respiratory syndrome (SARS), many scientists believe it is only a matter of time before the world is gripped by a deadly pandemic. Improving our understanding of these diseases may help us avert disaster from influenza and other severe respiratory viruses.

Surprisingly, the solution may be as simple as supplementing with higher-than-usual amounts of a common vitamin in the fall and winter months.2,4 The story behind this proactive approach to flu prevention begins in England more than a quarter century ago, eventually coming to fruition in California.

Popular Misconceptions About the Flu

First, some background on the influenza virus is in order. Epidemiological data from around the globe indicate that while flu cases are not entirely unheard of in summer, outbreaks of this virus peak soon after the winter solstice in temperate latitudes.5 For years, health experts have speculated that the explanation for this seasonality is that people tend to congregate indoors more often in winter, thus fostering rapid person-to-person transmission. However, in this age of ubiquitous air conditioning and 9-to-5 jobs, is there really much difference in the potential for interpersonal contact from one season to another? While children probably spend more time indoors in winter due to school schedules, what about adults?

In fact, the “huddling inside” explanation has never been found to account for the seasonal nature of influenza infection. In a recent article on influenza transmission, a respected researcher at the federal Centers for Disease Control and Prevention noted that no human experimental studies have delineated the person-to-person transmission of influenza. Instead, the virus appears to be spread through indirect contact, with transmission through respiratory droplets the most probable explanation at this time.5 However, since these minute respiratory particles are unavoidable, this theory fails to explain why influenza occurs more often in winter and why certain individuals demonstrate protection against the flu. This puzzle has led researchers to continue searching for factors contributing to the infectious nature of influenza viruses.

Unraveling the Influenza-Winter Season Connection

Dr. John Cannell, a California psychiatrist, is the chief author of a landmark theory that postulates that influenza epidemics are intimately linked to declining vitamin D levels.1

In California, Dr. Cannell works with patients at a maximum-security hospital for the criminally insane. In recent years, he had become aware that vitamin D is a unique compound with profound effects on human immunity. He had kept abreast of cutting-edge research demonstrating that vitamin D has numerous wide-ranging effects in the body, influencing everything from bone health and cancer prevention to blood pressure.1,6,7 Dr. Cannell also knew that an alarming number of otherwise healthy people are deficient in this crucial vitamin, especially in winter. “I realized that vitamin D is really quite different from other vitamins,” he recently told Life Extension.

Most of Dr. Cannell’s patients are African-Americans whose skin pigmentation interferes with the sunlight-driven production of natural vitamin D. This fact, combined with their confinement, led Dr. Cannell to suspect that his patients’ blood levels of vitamin D would be abnormally low. Testing confirmed this to be the case. After educating his patients about vitamin D’s potential benefits, Dr. Cannell prescribed routine supplementation with 2000 IU of vitamin D3 (cholecalciferol) daily. He says he would have given the men even higher doses, but 2000 IU represents the current “upper limit” of vitamin D intake recommended by the government-sponsored Food and Nutrition Board of the Institute of Medicine. By contrast, most adult multivitamins deliver just 400 IU of vitamin D, and a single eight-ounce glass of fortified milk delivers just 100 IU.7

Patients Stay Flu-Free Amidst an Epidemic

In the late winter of 2005, influenza broke out at the hospital. Ward after ward was quarantined, as patients were gripped with the chills, fever, cough, and severe body aches characteristic of the influenza A strain of the virus. “First, the ward below mine was infected,” says Dr. Cannell, “and then the wards on my right, left, and across the hall.” To his growing amazement, however, his own patients remained unaffected. “My patients had intermingled with patients from infected wards before the quarantines,” he notes. “I felt certain that my patients had been exposed to the influenza virus.” His patients’ enduring health in the midst of a local epidemic profoundly influenced Dr. Cannell’s thoughts on the relationship between vitamin D and immunity to the flu.7

He recalled the work of a pioneering British physician, Dr. R. Edward Hope-Simpson. Working in virtual obscurity, Hope-Simpson was catapulted to fame in the mid-1960s when he discovered the cause of shingles, a painful condition that affects adults. Thanks to Hope-Simpson, we now know that shingles results from the reactivation of latent chicken pox virus. After announcing this widely hailed discovery, Hope-Simpson turned his attention to influenza and was the first to document that in temperate latitudes, influenza A epidemics invariably peak in the month following the winter solstice. This pattern holds true for both the Northern and Southern hemispheres, and cases tend to rise and fall for about two months before and after the peak.8

Noting the obvious relationship between the decline in sunshine and rise of influenza, Hope-Simpson proposed that an undetermined “seasonal stimulus” must be responsible. Although he recognized that solar radiation had to be involved in evoking this seasonal stimulus, he was at a loss as to what the actual stimulus might be. Before his death in 2003, Hope-Simpson published numerous papers documenting the seasonal nature of influenza. While flu cases occasionally occur in summer, they rarely cause communal outbreaks. It may seem like common sense to acknowledge that flu is a winter phenomenon, but the fact had never been scientifically documented before. Hope-Simpson also noted, and other scientists have now confirmed, that flu outbreaks in the tropics tend to occur in the rainy season, when sunshine is scarce.4,7,9

Vitamin D and Immunity: What You Need to Know
  • An intriguing new theory suggests that diminished winter blood levels of vitamin D increase people’s susceptibility to influenza infection. Patients supplemented with vitamin D were shown to be completely protected against influenza infection, even while living in close proximity to people infected with flu.
  • Vitamin D has far-ranging effects on the immune system. Dangerous flu virus strains stimulate white blood cells to produce inflammatory cytokines associated with severe illness, while vitamin D protects against this effect. Vitamin D enhances the production of antimicrobial peptides, which are proteins that protect organisms from infection-causing microbes such as viruses. Vitamin D also activates essential infection-fighting immune cells known as macrophages.
  • People who live at higher latitudes, where less vitamin D is available from exposure to sunlight, experience a greater risk of illnesses such as multiple sclerosis, diabetes, osteoporosis, and certain cancers.
  • People seeking to optimize immune health and protect against viral flu infections, particularly elderly adults, should consider supplementing with high-dose vitamin D, especially during the winter months.

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