Why your weekend sleep-in might actually be leaving you exhausted

It’s Saturday morning and there’s no need to get out of bed. What could be nicer, then, than sticking a metaphorical finger up at the alarm clock, scrunching the duvet around you and drifting back to sleep until 11am.

But you won’t be alone in finding that these extra hours of sleep can have a surprising, counterintuitive effect. Rather than leaving you clearheaded and sharp, “oversleeping” can make a person feel groggy and lethargic for the rest of the day — and beyond.

It turns out there’s a proper scientific reason behind this muzzy head. Because, while the majority of studies have focused on the very real — and generally more distressing — consequences of too little sleep, or insomnia, there is an increasing body of research about the health downsides of sleeping too much.

In 2018, neuroscientists at Western University in Ontario studied 10,000 participants who recorded their own typical sleeping patterns. They then took a cognitive test, which comprised short-term memory tasks, verbal reasoning and spatial planning exercises.

The subjects reported the optimal amount of sleep for reasoning, verbal and “overall ability” was between 7.16 and 7.38 hours.

Perhaps unsurprisingly, the researchers found that regularly getting fewer than seven hours of sleep negatively affected the performance of the participants in the test.

Having a bit of extra sleep — around an hour — was seen to be beneficial.

“However, we also found sleeping more than 2.76 hours more than usual was associated with decreasing performance,” said Adrian Owen, the lead researcher. “This impaired cognition seen in long sleepers is actually driven by too much sleep; for example, longer sleep is associated with longer and more intense ‘sleep inertia’.”

Dr Sophie Bostock is a behavioural psychologist and sleep scientist. It’s this “sleep inertia” that gives us the Sunday-afternoon brain fog, she said.

“Our body clock is based on a set of genetically hard-wired instructions

If you haven’t had enough time awake on a Sunday, you won’t have enough of what we call ‘sleep pressure’ or the drive to fall asleep.

Dr Sophie Bostock

with a 24-hour rhythm,” says Bostock. “We are biologically programmed to do the same things at the same time: to start moving, eating and interacting socially. When our clocks get confused and are thrown out of sync, scientists call this ‘circadian disruption’. We still can operate, but are slightly sub-par.”

According to Bostock, this disruption can also spill over into the following day.

“If you haven’t had enough time awake on a Sunday, you won’t have enough of what we call ‘sleep pressure’ or the drive to fall asleep.

“A late start might leave you feeling ‘wired’ and you won’t fall asleep as easily.” It can also lead to a woozy Monday morning.

In addition, studies report that if you consistently need extra sleep, it might indicate other problems. A large French project from 2016 defined “long sleep” as more than 10 hours (it defined “short sleep” as fewer than five).

“In the general population, sleeping too much was associated with psychiatric diseases and higher BMI (body mass index) — though not other chronic medical diseases,” the study found.

Interestingly, the paper deduced that “long sleepers” were often female and from two age groups — between 15 to 25 years, or over 65, without university degrees.

However, the authors said people tended to sleep for a long time because they had health problems, and not the other way around. The study also pointed out that staying in bed too long could lead to depression, failing health, increased morbidity risk and decreased physical fitness.

A 2019 paper published in Harvard Health concluded that a minimum of seven hours is recommended for good health. Those who slept between seven and nine hours were typically at lower risk of becoming sick in the future.

However, Bostock agreed that your own sleep sweet spot might fall outside this calculation.

“Sleep duration can depend on various factors, including your genetic make-up, age and lifestyle,” she said.