Don’t lose sleep over your sleep, it’s genetically determined

What would you do if you had an extra 24 days of extra free time every year? Many of us dream of having more time in our busy lives, but it seems dreaming may also be the thing that’s preventing it. While most of us need seven to nine hours of sleep a night, some people, known as “short sleepers”, only need four to five hours to feel refreshed, and thanks to new genetic research we now know why.

Throughout history, influential figures have carried out their roles on very little sleep. Thomas Edison was known for calling sleep a waste of time and, apparently, Margaret

Thatcher ran the UK for a decade on only four hours of sleep a night. Even though Napoleon was rumoured to have taken daily afternoon naps, when asked about how much sleep people needed he is quoted as saying, “Six for a man, seven for a woman, eight for a fool.”

Dr Michelle Dickinson, creator of Nanogirl, is a nanotechnologist who is passionate about getting Kiwis hooked on science and engineering. Tweet her your science questions @medickinson

Being sleep deprived is bad for your health and, in addition to immediate problems with memory and mood changes, it has been linked to long-term issues including weight gain and a weakened immune system.

Previously “short sleepers” had been lumped into one category, which didn’t include the reasons why people don’t sleep for long enough. Insomniacs, for example, can have difficulty sleeping due to anxiety or stress and often complain that they need more sleep but can’t get it without help from medications. People with sleep apnoea can often wake themselves in the night with breathing and snoring issues and require assistance from physical devices like CPAP machines.

There is, however, another group of people who claim to wake naturally after only a few hours of sleep and, unlike the other groups, feel refreshed, energised and not in need of a nap.

Now, thanks to families who have allowed scientists to study their genome, this special short-sleeping group have been found to have a mutation in their genes that means they actually do physically need less sleep than the rest of us, giving them way more free time in the day — and it doesn’t seem to negatively affect their health.

The paper published this week in the journal Science Translational Medicine identified a mutation in the NPSR1 gene from two people from a family of short sleepers. This gene codes for a receptor that binds to neuropeptide S, which is associated with modulating sleep in the brain.

The researchers bred mice with the same NPSR1 mutation and found they too slept less, were more active and performed evenly on memory tests with normal mice.

In tests, the NPSR1 mutation meant that the humans needed two to four hours less sleep and the mice 71 minutes less sleep a night than average, resulting in an extra 24 days free time a year for the short-sleeping humans than the rest of us.

This research builds on another study published in PNAS last year that found a DEC2 mutation in human short sleepers. They also modified mice and found that when mutated, this gene, which controls levels of orexin — a hormone involved in regulating the circadian rhythm — can result in less sleep being needed with no measurable side effects.

So it seems that the amount of sleep that you need is genetically determined in the same way that your height or hair colour is. Some of us are born to need very little sleep while others require way more. Figuring out what kind of sleeper we naturally are could help us to reduce our expectations around what a “normal” amount of sleep actually is to help our bodies get a Goldilocks just-right amount for our needs.