Immune system and sleep.
Interesting page on the BBC website.
Towards the bottom of the page:-
What they discovered is that when the volunteers cut back from 7-1/2 to 6-1/2 hours' sleep a night, genes that are associated with processes like inflammation and immune response became more active. The team also saw increases in the activity of genes associated with the risk of cancer.
The reverse happened when the volunteers added an hour of sleep.
So the clear message from this experiment was that if you are getting less than 7 hours' sleep a night and can alter your sleep habits, even just a little bit, it could make you healthier. "Have a lie-in, it will do you good" - that's the kind of health message that doesn't come along very often.