Scientists ask why some people can't get out of bed.
Some people can function perfectly well on just a few hours of sleep, while others need a good 10 hours or more each day to remain chipper. Famously, Donald Trump claims that he only needs 3–4 hours in bed each night.
This isn't news, of course; these differences are well-documented. However, until recently, very little was known about why such variation exists.
A recent study set out to understand why some individuals appear to be able to burn the candle at both ends while others need to spend half of their lives under the sheets.
What is sleep for, anyway?
Overall, sleep is still a relatively mysterious beast. Despite spending around one third of our lives in slumber, its exact roles are still being unpicked.
A lack of sleep also seems to impair the immune system, so it might be involved there, too. We really don't know the full ins and outs of sleep, though.
When you consider that, when in the wild, animals must lie unconscious in the dark, surrounded by potential predators, you realize just how important sleep must be. But there is a counter-argument that lying still and quiet might be a better way to avoid becoming someone else's snack than moving around all night.
Either way, the fact that so much of our lives is dedicated to sleep means it must be pretty darned important.
The latest research to peer into the puzzle of sleep comes from the National Heart, Lung, and Blood Institute (NHLBI). Their findings are published this week in the journal PLOS Genetics.
In this study, the team wanted to get a handle on the mechanisms that underpin why some people need more sleep than others. The scientists hoped that the findings might offer some clues into two conditions at either end of the scale: insomnia, or not being able to get enough sleep, and narcolepsy, which is a condition characterized by intrusive "sleep attacks."
Scientists know that circadian rhythms, or daily cycles of sleep and wakefulness, are involved in our individual sleep patterns. These cycles are under genetic control, so it seems reasonable that genes are playing a part in sleep duration, too.
The current study aimed to pin down the elusive genes that might have a hand in this variation. The researchers — led by Susan Harbison, Ph.D., an investigator in the Laboratory of Systems Genetics at NHLBI — used a fruit fly model. Yes, it may seem bizarre, but fruit flies have their own version of sleep.
In fact, all animals that have been studied to date experience something at least a little bit like sleep, which is further evidence of sleep's importance.
They selectively bred 13 generations of fruit flies to produce either long-sleepers (18 hours per day) or short sleepers (3 hours per day), the Donald Trumps of the fly kingdom. And so, without adding, subtracting, or meddling with the fly's genetic code, they were able to produce strains with wildly different sleeping habits.
"What is particularly interesting about this study is that we created long- and short-sleeping flies using the genetic material present in nature, as opposed to the engineered mutations or transgenic flies that many researchers in this field are using."
Susan Harbison, Ph.D.
"Until now," she adds, "whether sleep at such extreme long or short duration could exist in natural populations was unknown."
They then compared the genomes of the two strains, looking for genes that varied between them.
A total of 126 differences across 80 genes were uncovered. These genes were involved in a wide range of vital developmental and cell signaling pathways, and some are known to be involved in brain development, memory, and learning.
According to the study authors, the fact that so many genes appear to be involved "suggests that sleep duration in natural populations can be influenced by a wide variety of biological processes, which may be why the purpose of sleep has been so elusive."
The good news is that neither the long- nor short-sleepers saw a reduction in lifespan — which is particularly good to know.
Although this is only a small part of a very large puzzle, it is a particularly interesting part. Additional research using human populations is likely to offer up more insight into the strange phenomenon we call sleep.