Sleep protects immunity, but how? Scientists have finally figured it out

Posted Wednesday, September 30, 2015---10:17 a.m.

(NBC NEWS)---Mom always said a good night's sleep helps fight off colds, and science recently confirmed it. But just how sleep protects us against illness has never been clear. An opinion paper in the journal "Trends in Neuroscience" may have finally solved the mystery. It's all about our body's memory, the scientists say. Healthy sleep, they believe, allows our immune systems to remember pathogens and fight them off at a later time.

"Why do we have to sleep?" asks Jan Born, a neuroscientist at the University of Tubingen and the paper's senior author. "We need it to form persisting memories in the psychological domain and also the immune domain."

Experts know that the brain encodes memories when people are in deep or slow- wave sleep. During this part of normal sleep, the brain stores information. Healthy sleep over time is key to retaining the information.

Born speculates that the same kind of memory encoding also occurs in the immune system.

While examining existing research, Born noticed that immune responses improved when people got a healthy amount of sleep. He cites a 2011 study, in which he participated, that looked at how sleep affects vaccines. To conduct the study, the researchers gave hepatitis A vaccinations to 27 participants and then kept half of them awake the following night. Those who did not get proper sleep after the vaccination had fewer antibodies in their system up to a year later, thus leaving them less able to protect themselves.

Born explains that sleep is what transfers information from the short-term memory to the long-term memory. "Why do you need two stages? Because both systems, the immune system and the brain, do not have unlimited capacity," Born says.

Sleep helps the immune system filter out the unneeded information and remember what Born calls the "gist information," details that allow the immune system to recognize a pathogen similar to one it has already faced, and then counter it with the effective immune response.

When people fail to get proper rest, the immune system can't store that gist information and it struggles to fight off pathogens.

The new theory is a reminder that good sleep is essential, says Dr. Nathaniel Watson, president of the American Academy of Sleep Medicine and co-director of the University of Washington Medicine Sleep Center.

"This is just further evidence of the importance of sleep to our overall health and wellbeing," said Watson, who was not involved in the research.

"We spend one-third of our lives sleeping," says Watson. "We need to pay attention to it and prioritize it in our lives."

Copyright 2015: NBC News