The days are getting shorter and the nights are getting cooler. Fall begins this Friday. That means that any day now, we’ll start seeing news stories about "flu season" and getting vaccinated. But why is there a flu season in the winter? The influenza virus is around all year, and there are people catching it throughout the year — just not very many. So why are so many more of us susceptible when the days get short? Well, it’s because the days get short:
Now a group of researchers has come up with a novel answer to the conundrum. The "seasonal stimulus" behind the annual winter flu epidemics is a lack of vitamin D due to shorter days and lack of sunlight.
And they have even suggested that by taking a mega-dose of the vitamin at the first sign of the illness, its worst symptoms might be alleviated – which could prove to be a potential life-saver in the event of the threatened avian flu pandemic.
…The traditional explanation for the winter flu epidemics is that we tend to crowd indoors in the winter months, which aids the spread of the virus. Fifty years ago, when millions of manual labourers earned their living working outdoors, that may have been true.
But in the modern world, where most people work in offices and factories, travel on buses and trains, and share the same indoor spaces in summer and winter, the explanation rings hollow. Some of the people most vulnerable to flu – elderly people living in nursing homes – are there all year round yet are at greatest risk from the virus in winter, much like everybody else.
A glass of milk contains about 100 units of vitamin D, and the RDA (recommended daily allowance) is 400 units. But twenty minutes in the summer sun can produce up to 20,000 units in your body, and levels like that were the norm for humans until very, very recently:
Throughout evolutionary history, humans obtained tens of thousands of units every day from the sun. Even after migrating to temperate latitudes, where skin colour rapidly lightened to allow for more rapid vitamin D production, humans worked outdoors. Only in recent decades as we have increasingly lived and worked indoors, travelled in cars and lathered on sunblock have levels of vitamin D sunk chronically low, according to Dr Cannell.
It may not replace the flu shot, but I strongly recommend a hefty daily dose — say, 2,000 units or more — of vitamin D during the fall and winter months. It’s not just to ward off the flu and bolster your immune system — vitamin D plays many other important roles. The U.S. government’s RDA is enough to prevent rickets, but woefully inadequate for optimum health. That, by the way, is true of many vitamin RDAs — they’ll keep you from having clinical signs of deficiency, but that’s far below the optimum levels for health.