When we fall ill, we are always advised to sleep, get a good night’s rest, and stay at home – if possible, stay in bed. This might not be all too difficult: after all, we often feel weak when we are ill; and we often do want to sleep when we have infections, such as typhoid fever or the flu.

What is the reason for this ever-reliable exhortation of “Sleep and rest?” And why do we feel sleepy when we are sick? Is there a link between sleep and the immune system?

Before you can establish a connection between rest and recuperation, you have to know how the immune system works. When your body picks up a pathogen, such as a virus or a bacterium, your body sends out cells to recognize it. Once these cells find out what the invader is your body launches a defense response to kill the infection. This would entail you having to endure a fever, body pains, sometimes even vomiting or loose bowel movement as your immune system puts up a fight. If you get well, your immune system can create memory cells, which will protect you from future infections.

One such molecule that promotes destruction of invaders is called interleukin-1, or IL-1. IL-1 encourages special blood cells called B lymphocytes to produce antibodies, which lead to viral destruction. IL-1 also allows T lymphocytes, another type of immune system cell, to attack bacteria.