As people get older, their sleep cycle start to shift, which means older people tend to go to sleep at much earlier times. Here's the crazy part: a little blood-related trickery can make young people sleep just like the elderly.
Our sleep cycles are governed by the circadian genes in our cells. These genes are expressed at different strengths during the day, with the peak periods corresponding to when we're awake. These circadian genes work in a 24-hour cycle, but the precise times at which the genes peak and dip shifts earlier as people grow older. That's why older people tend to get up and go to bed much earlier than their younger peers.
But these things aren't absolutes, and researchers at the University of Zurich have discovered how surprisingly easy it is to manipulate people's circadian clocks. If you take a young person's skin cells and grow them in the blood serum of an older person, the circadian genes themselves will essentially age. It appears there's a hormone or some other unknown agent in the blood that can have remarkable influence over people's circadian clocks.
Researcher Steven A. Brown explains:
"A gene that had a peak expression at a particular time in cells from younger individuals might have this peak two hours earlier in the presence of serum from older individuals. Human behavior shifts because activities normally done at one time of day are now done earlier or late. Cellular 'behavior' shifts in the same way: Something that the cell normally does at one time of day is done instead at another."
Once we isolate this serum, it's possible it could become a drug for resetting people's sleep schedules - a boon for people suffering insomnia or sleep cycles that are out-of-whack.
While the blood serum clearly can have a powerful effect on when people sleep, Brown says it's not the only factor for why older people go to sleep earlier than younger people. Other factors might include the fact that older people tend to spend less time outside and thus are exposed to less direct sunlight. Indeed, these environmental factors might be somehow tied to what's going on in our blood, but Brown admits that we simply don't understand enough yet about how this all works.