Lack of Vitamin D may be why flu goes wild in midwinter

http://thechronicleherald.ca/Science/540205.html

Catch rays, nix the flu
Lack of Vitamin D may be why disease goes wild in midwinter



The winter flu season could be the result of our reduced exposure to
sunlight, according to a review scheduled to be published in print in
Epidemiology and Infection next month.

The seasonal tide of influenza has baffled epidemiologists for ages.
The flu is always at its worst in the months following the winter
solstice, and pandemics tend to hit at this time too, but nobody is
certain why.

If that puzzle could be unpicked, the information could be used to save
lives; in an average year, about one million people die worldwide from
influenza-related illnesses. In a flu pandemic, such as occurred in
1918, millions of people can die.

In 1981, Edgar Hope-Simpson, a British epidemiologist, suggested that
influenza's seasonality might be linked to solar radiation. Very few
epidemiologists took the idea seriously. But in the years since,
evidence has continually surfaced that vitamin D, created when solar
radiation strikes the skin, plays an important role in our immune
system.

Now, 25 years later, a review of the evidence suggests that
Hope-Simpson's theory of an influenza seasonal stimulus be rigorously
tested.

"Winter brings a host of confounding factors associated with the
influenza," says Edwin Kilbourne, professor emeritus at New York
Medical College. Low relative humidity favors influenza virus aerosols,
and indoor crowding facilitates transmission. Autumn brings young
children together in schools, and Christmas travel mixes up previously
separated populations.

"But there's more to it then just environmental conditions," says
Kilbourne. "Controlled experiments with my laboratory mice have shown
that even after careful control of environmental factors, including
crowding and humidity, there remains a seasonal factor that slightly,
but significantly, affects transmission of influenza."

John Cannell of Atascadero State Hospital, California -- lead author on
the new review and executive director of the nonprofit organization the
Vitamin D Council -- thinks vitamin D might be the missing link.

He points to one study, conducted in St. Petersburg and repeated in
Krasnodar, Russia, showing that young men inoculated with live
attenuated influenza virus were eight times more likely to develop
fever and evidence of an immune response just after the winter solstice
then they were during the summer months.

Another showed that children in India with vitamin D levels of less
than 10 nanograms per milliliter were 11 times more likely to have
respiratory infections than those with higher levels of the vitamin.

And a series of studies from the 1930s showed that cod-liver oil, which
is rich in vitamin D, can reduce viral infections by 50 per cent in
adults taking a daily dose over 4 months.

"Within a few minutes of summer sunbathing, our bodies make about
20,000 international units (500 micrograms) of vitamin D," notes
Cannell. "We have evolved a system that makes lots of the vitamin very
quickly. There is no doubt in my mind that this happened for a good
reason." Vitamin D is known to regulate calcium in the blood and
maintain bones, but Cannell thinks its role in immunity is just as
important.

Kilbourne isn't convinced. "My mind is open on this, but persuasive
evidence has just not been presented," he says. His seasonally
flu-ridden mice, he notes, were in the basement away from any sunlight.

"The paper raises more questions than it answers," agrees James Cherry,
a specialist in pediatric infectious disease at the David Geffen School
of Medicine, University of California, Los Angeles. "However, the
hypothesis should be easy to prove or disprove with a controlled blind
study," he adds. Cannell is keen for that study to happen.

"It is premature for doctors to recommend vitamin D as a treatment or
preventative against flu," Cannell says, but he himself is taking no
chances. Cannell takes 125 micrograms of vitamin D a day during winter
-- much more than the U.S. government's recommended dose. He advises
doctors to be on the lookout for vitamin D deficiency and treat it
aggressively.

*************

TC

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