No matter how exhausted we are from a long week of work, early-morning exercise classes and late-night TV bingeing, many still find it impossible to sleep in when given the chance. Here’s the weird reason why, and how to fix it.

For many adults juggling a full-time job, gym memberships, needy pets and even needier children, finding the time to fit our responsibilities into a single day usually requires setting an early morning alarm. 

But when the weekend rolls around (and the kids have yet to stir), there’s no greater feeling than knowing you have nothing to do, and nowhere to be (Pilates and coffee catch-ups aside).

So why, without rhyme or reason (and of course, an alarm), do our eyes blink open on a Sunday morning before the sun has even risen?

Gone are the days of sleeping in until noon, woken up only by the sound of our parents’ insistent banging on the door. While there aren’t too many things people miss about their teenage years, the ability to sleep undisturbed well into the late morning is certainly one of them. 

Despite staying up later into the night as we age (thanks to a combination of responsibilities, captivating Netflix crime documentaries and free will), our internal alarm clocks seem to be going off earlier and earlier as the years go on.  

The common phenomenon, experts say, is a result of a combination of different factors. 

Our inability to sleep in beyond a reasonable hour is a natural side effect of ageing, according to Dr Sairam Parthasarathy, the director of the Center for Sleep and Circadian Sciences at the University of Arizona Health Sciences.

As well as rising earlier in the morning, people tend to opt for an earlier bedtime as they age. Like every body function, the nerves responsible for cueing the brain ahead of major milestones through the day (such as meal times and bedtime), undergo natural degeneration as we age. 

As a result, our sense of time can shift, as the body seeks rest earlier than it might once have. Of course, an earlier bedtime leads to an earlier wake-up time, too, says Dr Parthasarathy.

“The wiring of the brain is likely not sensing ... and responding to the inputs as well as it should because it’s an aging brain,” explains the sleep expert to Huffpost. Inputs that usually help anchor the brain’s sense of time include physical activity, sunlight, meals, social cues and sunset. 

The brain’s dwindling ability to process and respond to these cues as we get older not only shifts our rest time forward but can also lead to disruptions in our ability to sleep through the night. 

It’s part of the reason newborns can blissfully sleep through the sound of a vacuum, but a gust of wind can be enough to wake us from our slumber. 

Of course, the brain’s natural degeneration isn’t the only factor at play when it comes to our declining ability to sleep in all morning. If you’re someone guided by habit and routine, ignoring your weekday 6 AM alarm every Sunday might just be too confusing for your body. 

Additionally, health markers such as your hormone levels, bladder function and any chronic illnesses could also be contributing to your early wakeup time. 

The quality of our sleep also changes significantly as we age, specifically with how we progress through each phase of sleep, between light, deep and REM. Older adults typically experience more light sleep than deep sleep, meaning they are more prone to waking up as a result of disturbances. 

How to prolong your wake-up time

Despite the countless times we’ve been told to steer clear of screens, bright lights and anything that might stimulate our brains too much before bed, experts say the key to fixing our sleep-in issue lies in embracing these very habits. 

In order to stretch out our wake-up time, we first need to prolong our bedtime, encouraging the brain to hold its melatonin production. 

Dr Parthasarathy recommends making the most of the last hours of natural sunlight and even exposing ourselves to artificial and bright lights before bed. Bright lights will help convince the brain that the sun has yet to set, in turn helping the body to stay up past your usual bedtime. 

You heard the expert; save your doom scrolling and reel exchanges for later this evening.