Link between sleep and immune function, say scientists

You know that groggy, tired feeling at the beginning of a bad cold? It turns out this may be an important part of the healing process.  While scientists have suspected for 40 years that sleep and recovery were connected, they had little evidence.

Now, researchers at the Perelman School of Medicine at the University of Pennsylvania have investigated the relationship between sleep and the immune system using fruit flies.  What they found may help to explain the role that sleep plays in helping us to recover from sickness.

Why fruit flies?

You may wonder, “What do fruit flies have to do with humans?”   Dr. Julie A. Williams, PhD., who conducted the study with Dr. Tzu-Hsing Kuo, PhD, explained that fruit flies share many genetic factors with humans. However, unlike humans, fruit fly genetics provide a much simpler way to examine basic biologic processes.

Sleep – a response to infection?

In the first of two experiments the researchers compared how fruit flies recovered from bacterial infection. One group of flies was sleep-deprived prior to infection while the second group was not.  After  infection, both groups of flies slept longer than normal.

The researchers called this phenomenon the “acute sleep response.” Both fly groups exhibited this response, but the sleep-deprived flies slept longer than the control group.  Unexpectedly, the sleep-deprived flies had a better survival rate. “To our surprise they actually survived longer after the infection than the ones who were not sleep-deprived,” Williams explains.

The experimenters also examined a group of flies that were deprived of sleep after infection. They found this change in timing made little difference, as long as the flies had enough total recovery sleep after infection.

“We deprived flies of sleep after infection with the idea that if we blocked this sleep, things would get worse in terms of survival,” said Williams. “Instead they got better, but not until after they had experienced more sleep.”

Extra sleep before an illness

In the second experiment, the team used a drug to regulate fruit fly sleep patterns before infection.  In a group of flies that slept longer prior to infection, the flies had greater survival rates than flies that slept normally, and they cleared bacteria from their bodies more efficiently.

“Again, increased sleep somehow helps to facilitate the immune response by increasing resistance to infection and survival after infection,” said Dr Williams.

The take-home message

The researchers believe they have found some preliminary evidence that when you’re sick, sleeping as much as possible is beneficial to your recovery.

Whether you sleep more before getting sick or after your illness, increasing the total amount of sleep you receive may give your body the boost it needs to clear an infection.

In conclusion Dr Williams said “these studies provide new evidence of the direct and functional effects of sleep on immune response and of the underlying mechanisms at work….  “when you get sick, you should sleep as much as you can — we now have the data that supports this idea,”  So next time you’re ill, take a lesson from our fruit fly friends and prioritize sleep.

Read more about these findings from Penn Medicine.

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