Hazy Shade of Winter Flu
As kids, we were taught that going outside in the winter without a hat and gloves was an open invitation to colds and flu. "You'll catch a cold!" was my mother's mantra from November through March, as my siblings and I roamed our drafty old farmhouse with bare feet, or ran outside without a coat.
Then I went to college and medical school and learned how colds and flu are caused by viruses, not bare feet and heads. I tried to explain this to my mother, but she was never convinced. "Then why is winter the cold and flu season?" she'd ask. I'd sigh and roll my eyes - but I didn't really have a rebuttal.
Now it seems Mom was on to something. New research says there is a real link between colds and flu and wintertime. But it's not the temperature that gets you: it's the lack of sunlight and the resultant lack of vitamin D.
I know, I know - I just wrote to you about the importance of vitamin D, and how it can help you prevent cancer, arthritis, even multiple sclerosis. But when I read about this new research, I just couldn't wait to share it with you.
Seems back in the early 80s, a British physician named R. Edgar Hope-Simpson published data showing a correlation between flu epidemics in the northern hemisphere and the winter solstice - the shortest day of the year. Hope-Simpson reported that flu cases tended to spike right around the winter solstice - and theorized there was some sort of "seasonal stimulus" that triggered them.
Hope-Simpson didn't get a lot of traction for his "seasonal stimulus" theory at the time. But now, more than 20 years later, a team of researchers at Harvard, Boston University and NIH have resurrected Hope-Simpson's work. And they've taken it one step further: they propose that the "seasonal stimulus" is low levels of vitamin D.
The new paper draws its conclusions not just from Hope-Simpson's work, but from more than 70 years of research that struggled to explain why cold and flu are more prevalent in the winter. Temperature alone had long ago been ruled out, after experiments that put virus-exposed subjects in cold water baths or refrigerated rooms failed to show a correlation. And the old theories about winter-time indoor overcrowding don't hold true in today's world. But interestingly, much of the old data did support the sunshine connection - for instance, studies that showed that cold and flu season in tropical areas coincided with the rainy season.
The authors suggest that healthy levels of vitamin D in the blood trigger the production of an immune system compound called cathelicidin. Studies have shown that cathelicidin attacks viruses, fungi, and bacteria, though it hasn't yet been tested directly against the influenza virus.
I've long been vocal on the importance of vitamin D. It's critical to healthy bones, and as I recently told you, has also been shown to protect you from many types of cancer, arthritis and MS. This study may open a whole new school of thought on vitamin D's relationship to immune function.
If you're concerned that you're not getting enough vitamin D (and you should be), the best strategy is to know your vitamin D status. Ask your doctor to order a 25 hydroxy vitamin D blood level test. It's a simple blood test that provides the most accurate assessment of vitamin D in your body. The results should be at least 30 nanograms per milliliter, but I like to see levels above 40 nanograms per milliliter.
Even armed with test results, most people find that a supplement is a wise insurance policy. Experts recommend 15 minutes in the sun each day, exposing your bare face and arms, but that can be difficult in winter months. For just about everyone not living in a warm sunny climate, I recommend taking 1,000 IUs of vitamin D year round plus an extra 1,000 IUs from November through April (2,000 IU daily total). Worried about toxicity? Experts now estimate toxic levels are upwards of 10,000 IUs a day, so my recommendation is obviously well within the safe range. If you're taking a supplement and getting sunshine, too, don't worry -- your body has protective feedback mechanisms that prevent the production of too much vitamin D.
