How just two nights of bad sleep makes you feel five years older

Just two nights of bad sleep in a row can make you feel nearly five years older, a study has found.

Researchers also discovered that consistently sleeping badly over a prolonged period makes you feel a decade older than you would if you consistently sleep well.

Scientists from the Karolinska Institute in Sweden carried out two studies involving 615 people aged between 18 and 70.

One study found that two consecutive nights of poor sleep – defined as four hours or less – made a person feel 4.4 years older than they would if they had nine hours’ sleep.

The other showed that every night of poor sleep over a 30-day period made a person feel 2.8 months older.

Meanwhile, both studies found that the difference between sleeping well most of the time – with a Karolinska Sleepiness Scale (KSS) score of one – and badly (a KSS score of nine) amounted to a 10-year difference in “subjective age”, or the aged that you feel.

Feeling extremely alert made people feel four years younger than their biological age, while extreme sleepiness made them feel six years older.

“This means that going from feeling alert to sleepy added a striking 10 years to how old one felt,” said Dr Leonie Balter, of the Karolinska Institute. “I expected insufficient sleep to be associated with subjective age, but it was surprising that it had such large effects.

“Sleepiness is an important state that signals our need for rest and reduces our energy levels. Feelings of reduced energy and motivation may not only cause someone to feel older but it is also essential for engaging in activities important for health, as it enables being physically and socially active.”

In her study, Dr Balter (inset) did not look at biological mechanisms underpinning the relationship between lack of sleep and how old you feel but plans to do so in future. Previous studies have looked at the effects of poor sleep on mental and physical health, but this was the first to examine how old it makes people feel and to put a number on it. Dr Balter’s findings are published in the journal Proceedings of the Royal Society B.