Sep 01 2015

Sleep and Health

Getting sufficient sleep is very important to overall health. It is an often overlooked aspect of health. I frequently have patients with multiple complaints who inform me, only when asked, that they have terrible sleep. They did not make the connection between their sleep and their symptoms, however.

Good sleep has been tied to longevity. A review of studies found that getting <6 hours of sleep on average per night was associated with a 12% increased risk of death. The same review found that getting >9 hours of sleep a night was associated with a 30% increased risk of death.

It is difficult to determine cause and effects with these studies. Sleep may simply be a marker for other health variables. People who sleep over 9 hours, for example, may do so because they are unhealthy for other reasons.

Even still, it is plausible that lack of sleep is stressful to the system, especially brain function, and therefore sleep disorders should be identified and treated. Don’t overlook the importance of good sleep.

A recent study sheds additional light on one aspect of sleep – the possible association between lack of sleep and susceptibility to infections. This connection has long been suspected. A 2009 study by Cohen at al found that decreased sleep efficiency was associated with a 5 fold increase in the risk of developing clinical symptoms when exposed to a rhinovirus (a virus that causes the common cold).

Cohen and colleagues have now conducted a follow up study. They looked at 164 healthy volunteers who reported their sleep, but also were monitored for sleep duration. Again they exposed them to rhinovirus. Those with <5 hours sleep had a 4.5 x increased risk of developing the cold. Those who slept 5-6 hours had a 4.2 times risk compared to those who slept more than 7 hours. Those who slept 6-7 hours had no increased risk.

The researchers found that “other sleep variables obtained using diary and actigraphy were not strong predictors of cold susceptibility.” This makes me wonder how many other variables did they look at, and did they adjust the statistics accordingly.

Definitely this research requires some independent replication. A connection between sleep and immune function is plausible, however. Stress increases corticosteroid release which suppresses the immune system. A 2012 study found that lack of sleep was associated with decreased antibody production after hepatitis B vaccination, supporting a causal connection. Cohen was also a co-author on this study.

Conclusion

This series of studies by Cohen’s group suggests that lack of sleep is associated with impaired immune function and increased susceptibility to infections. However, I would consider these results preliminary because they are all coming from one group and the study design was more exploratory than confirmatory (looking at multiple variables, for example).

Before we conclude that this effect is probably real we will need some independent replication.

In the meantime, however, the recommendation that would flow from this research is a good one anyway. Optimizing sleep likely has multiple benefits, even if resistance to infection does not pan out as one of them.

I consider getting enough sleep like getting regular exercise. We can quibble about the evidence for the exact benefits, meanwhile it’s pretty clear that exercise and sleep are good things.

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