Sleep and the Common Cold

January 27, 2009

Sleep and the Common Cold Competency 

# 7  Sleep                            Reference: Archives Internal Medicine Jan 2009 p 62-67 

 Can you imagine being willing to have your risk for a cold being tested in relationship to how much sleep you get?  That’s what Dr. Cohen and partners were successful in getting  153 healthy men and women to do.  For 14 days they measured exactly how long they slept, and then had the cold virus, rhinovirus, squirted up their noses.  

What they found is fascinating.  Turns out that getting less than 7 hours of sleep turns into 3 times greater risk of getting a cold.  And sleep efficiency below 95% had a 5.5 times increased chance of getting a cold versus someone who was 98% efficient. What’s sleep efficiency?  Very simple, it’s the fraction created by dividing the amount of time you estimate you are sleeping divided by the time in bed.  Volunteers were asked each day to report how long it took them to fall asleep, and how often they woke up and had a hard time falling back to sleep.  Those minutes were subtracted from the total.  A running average overall 14 days was added up to get the fractions. 

 We have known for a while that less sleep results in lower measures of antibody response to both hepatitis A and to influenza vaccination.  We also know that sleep deprivation results in reduced natural killer cell activity and increased levels of inflammatory hormones.  So something magical happens to your immune system while you sleep.  We naturally have about 90-minute cycles of sleep in which we run through different stages of sleep, so 7 hours comes to about 5 cycles.  

As we get older, our sleep becomes more fragile and lighter, and our awareness of our bladders becomes more acute.  This study used younger folks (average in the thirties and maximum early 50s) so its implications for folks in their 60s and 70s is uncertain. This is the first good research to prospectively show the risk.  Apparently, sleep efficiency, what percentage of time you stay asleep, is even more important than the total amount.  Time to talk about how to train you to sleep.  That’s next week. 

 WWW.  What will work for me?  Well, hearing that less than 7 hours is as high a risk for heart disease as high blood pressure and that I get fatter and more diabetic has me in froth.  So, I’ve made changes.  Seven hours in the sack.  Minimum.  Awake or not.  Interestingly enough, when I know the rule and I look at the clock radio and it’s 430 and I feel wide awake, I tell myself,  “It’s against the rules to get up”.  And sure enough, I’m falling back asleep.  Not getting as much work done.  Oh well... Feels like I’m back in boarding school.

This column written by Dr. John E Whitcomb, MD, Brookfield Longevity, Brookfield, WI (262-784-5300)