I’m always on the lookout for clues as to why I get sick more frequently than most folks and why, when I do get sick, my colds last so much longer. I came across this study which adds additional weight to my theory that one cause is that for reasons I cannot really do much about, my sleep sucks.

Poorer sleep efficiency and shorter sleep duration in the weeks preceding exposure to a rhinovirus were associated with lower resistance to illness…

There was a graded association with average sleep duration: participants with less than 7 hours of sleep were 2.94 times (95% confidence interval [CI], 1.18-7.30) more likely to develop a cold than those with 8 hours or more of sleep. The association with sleep efficiency was also graded: participants with less than 92% efficiency were 5.50 times (95% CI, 2.08-14.48) more likely to develop a cold than those with 98% or more efficiency

 

What’s especially interesting here is the sleep efficiency bit. I track my sleep using my Apple Watch and an application called AutoSleep. It is fairly reliable and I have at least a year’s worth of sleep data collected now. It’s interesting to see how lower sleep efficiency relates to lower heart rate variability when I dig into the Health app. This quote, especially, was striking:

even a minimal habitual sleep disturbance (sleep losses of 2%-8%, 10-38 minutes for an 8-hour sleeper) is associated with 3.9 times the risk of developing a cold.

AutoSleep data on the iPhone

What’s a bit confusing for me though is how many nights in a given period can sleep efficiency fall below 92% before that 3.9x risk occurs. Surely one night or two nights over a 2 week period (the length of the study) can’t cause this 3.9x risk. 

Still, taken as a whole/moving average over a 2 week period, it does seem like one of the AutoSleep numbers I should be looking at it sleep efficiency. 

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