Stress, sleep, and the ageing brain: why rest is protective

Do you ever wake in the middle of the night with your mind racing, only to drift off again just before dawn? Or find yourself lying in bed, exhausted but wired, wondering why your brain won’t switch off? This is such an incredibly common experience – especially as we age. As we move through midlife and beyond, many people notice that stress feels heavier and sleep comes less easily – yet both are vital for keeping our brains healthy as we age.

Why sleep matters more than we realise 

Sleep isn’t simply “down time”. It’s an active, restorative process during which the brain clears out waste, consolidates memories and resets its chemical balance. Think of it as a nightly rinse cycle. During deep sleep, the brain’s glymphatic system – a kind of cleansing network – flushes away metabolic debris, including proteins linked to Alzheimer’s disease. When we don’t sleep well, those substances can linger and gradually accumulate.
 

Short-term sleep loss leaves us irritable, forgetful and less focused. But over years, chronically poor sleep can nudge the brain toward faster ageing. The good news is that it’s never too late to support better rest. Even small improvements in sleep quality can make a measurable difference to mood, memory and long-term cognitive function. If good quality restorative sleep is elusive for you, try going to bed and waking up at consistent times. Dim lights after sunset and expose yourself to morning light soon after waking – it helps reset your internal clock. You may also like to consider your relationship with caffeine and alcohol. Both can interfere with the deep stages of sleep that the brain needs most. Aim to stop caffeine after midday, and give your body several alcohol-free nights each week (at least). 

The hidden cost of constant stress 

It’s easy to think of stress as something that lives only in our thoughts, but our bodies are like a living record of our resilience. When stress hormones like adrenaline and cortisol stay high for too long, they can disrupt nearly every system in the body – including the brain. Elevated cortisol has been linked to smaller hippocampal volume (the hippocampus is the brain’s memory hub), slower information processing and a greater risk of cognitive decline. 

What makes modern stress tricky is that it rarely switches off. We’re not running from lions; we’re juggling family, finances, health and the endless to-do list. When we perceive these things as sources of stress, or face everything in our day with a sense of pressure and urgency, the brain interprets that ongoing pressure as a threat, keeping us in a mild but constant state of alert. Over time, that “always on” state leaves us feeling wired but weary – and our sleep pays the price.

How stress and sleep shape each other 

Stress makes it harder to sleep; lack of sleep makes us more reactive to stress. It’s a frustrating loop that many people find themselves caught in. When cortisol rises in the evening – the time it should be winding down – we tend to lie awake replaying the day. The next morning, fatigue makes small challenges feel bigger, which raises stress hormones all over again.
 

Breaking that cycle isn’t about eliminating stress completely (that’s impossible), but learning to regulate it. Gentle, slow-paced breathing before bed, reading something uplifting instead of scrolling a screen, or taking a short walk after dinner can all help to lower evening cortisol levels. Even five minutes of slow, diaphragmatic breathing tells your nervous system, you’re safe now; you can rest.
 

Stress resilience also comes from learning to take a step back from our thoughts – to notice them without immediately believing or reacting to them. When we’re caught in a loop of worry or “what ifs,” the brain can’t tell the difference between a real threat and a perceived one, so it keeps stress hormones elevated. Simply pausing to observe a thought, “Ah, there’s my mind running ahead again”, helps interrupt that pattern. Practices like mindfulness, journalling, or even talking things through with someone you trust can all strengthen this ability. Over time, you start to create more space between what happens and how you respond to it. That space is where calm lives. It’s where your brain and body can finally exhale, allowing rest and repair to take place.