Sleep, Stress and the Brain: Why Quality Rest Matters

By Patrick Holford

What does any animal, perhaps your dog, do after exercising or going for a walk?

Sleep.

Sleep is how the brain recovers. There is now overwhelming evidence that sleep is a ‘brain essential’ and just like Goldilocks, it seems we need just the right amount. Getting too much, or too little, increases our risk for cognitive decline.

The optimal amount of sleep for brain health appears to be a total of seven hours. This does not necessarily need to be in one uninterrupted stretch – a study found that napping after physical activity can reduce the risk of cognitive impairment.

However, those consistently getting less than seven hours of sleep may be doubling their risk of age-related cognitive decline. A UK study of Whitehall civil servants, which began in the 1980s, found that persistent short sleep at ages 50, 60, and 70 was associated with a 30% increased risk of dementia. Sleep loss does not just increase long-term dementia risk – it also reduces empathy, increases negative emotions, and impairs next-day functioning.

Why Sleep Is Essential to Brain Health?

Think of sleep as the brain’s housekeeper. During sleep, circulation of blood and cerebrospinal fluid improves, helping to clear out waste products from brain metabolism. These include harmful oxidants and amyloid protein, the latter linked to Alzheimer’s and brain inflammation – which can begin accumulating after just one night of poor sleep.

One key agent in this nightly brain cleanse is melatonin. As night falls, our brains convert serotonin into melatonin, primarily in the pineal gland – referred to by Descartes as the seat of the soul, and known in yoga as the ‘third eye’ chakra.

Sensitive to light via receptors behind the eyes, the pineal gland is the only endocrine organ in direct contact with the external world. Darkness triggers melatonin production, while exposure to light – including screen use before bed – suppresses it.

Melatonin helps keep us in sync with the circadian cycle. Some frequent flyers even use melatonin supplements to overcome jet lag and adjust their sleep rhythms more easily.

More than just a sleep aid, melatonin acts as a powerful antioxidant – disarming damaging oxidants, restoring mitochondrial energy production, and acting as an anti-inflammatory. It has been used to support recovery in cancer, COVID-19, and cardiovascular conditions. Reduced brain melatonin levels and circadian disruption are also observed in individuals with cognitive decline.

Why Dreaming Matters?

Sleep isn’t just for rest – it’s a deeply active process. About 30 minutes after falling asleep, we enter deep sleep, marked by slower breathing, a reduced heart rate, and lower blood pressure. This phase restores and repairs bodily tissues. About 90 minutes in, we shift into REM (rapid eye movement) sleep – where most dreaming occurs.

REM sleep is critical for brain health. Each night, we cycle between deep, light, and REM sleep three to five times, with REM ideally making up about 25% of total sleep.

REM and deep sleep phases also see increased production of growth hormone, which supports tissue repair. Meanwhile, melatonin helps clear metabolic waste. However, under stress, cortisol levels rise and suppress REM sleep and growth hormone production, reducing the brain’s ability to recover. Sleep-deprived individuals tend to experience more REM when they finally do sleep, suggesting REM plays a key role in emotional processing.

One theory suggests that dreams help us metabolise suppressed emotions – fear, anger, sadness – stored during our busy days. If you have a vivid, emotional dream, it may be worth tracing it back to unresolved feelings from the previous day.

How Chronic Stress Disrupts Sleep and Brain Function?

Chronic or intense stress – such as bereavement, illness, or financial strain – has been shown to increase the risk of cognitive decline and dementia (10). However, good sleep can help process a stressful day.

The perception of control matters, too. Studies show that high job demands combined with low control are strongly linked to an increased risk of depression and cognitive impairment. Examples might include caregiving for a loved one with dementia while navigating health services, or working in a high-stress job without the resources to make meaningful changes.

Your Brain on Cortisol: The Hippocampus Feedback Loop

Two hormones mediate stress: adrenaline (short-acting) and cortisol (longer-acting). Adrenaline prepares you to act quickly – it’s the fight-or-flight hormone. Cortisol helps regulate energy and alertness throughout the day.

In the morning, cortisol naturally rises to get us going. It should fall in the evening to support sleep. But chronic stress disrupts this rhythm. If cortisol stays high at night, sleep is disturbed. If it’s too low in the morning, you may feel foggy and reach for caffeine.

Excess cortisol impairs memory, slows thinking, lowers social functioning, and raises the risk of dementia. What’s happening in the brain is that cortisol overstimulates the hippocampus, which is responsible for memory and emotional regulation. With prolonged stress, this feedback loop fails – the hippocampus shrinks, and cortisol levels remain elevated, accelerating brain ageing.

Short-Term Relief, Long-Term Harm: Sugar and Alcohol as Stress Crutches

Oscar Ichazo described how we reach for compensations under stress. Unfortunately, many – like alcohol and sugar – backfire.

Alcohol temporarily boosts GABA, calming the nervous system and reducing adrenaline. But the effect is short-lived. Drinking too much reduces GABA receptor sensitivity the next day, leaving us more anxious. In the long term, alcohol is neurotoxic and increases dementia risk. It also disrupts sleep architecture, impairing the brain’s ability to repair itself.

Sugar triggers dopamine and activates the brain’s reward circuits, making us crave more. It also spikes the adrenal system, amplifying stress and cortisol levels. Fats and proteins do not have this effect – this is unique to sugar.

So, when we use sugar or alcohol to manage stress, we often wake up feeling more anxious and foggy. This leads us to reach for caffeine and more sugar, which spikes cortisol again, leaving us even more depleted by evening – creating a cycle of stress, poor sleep, and accelerated brain ageing.

Simple Ways to Break the Cycle

The good news? You can reverse this pattern. Start here:

• Prioritise seven hours of quality sleep each night.
• Identify and reduce common stress triggers.
• Be mindful of alcohol and sugar intake.
• Find positive outlets: yoga, walking, journaling, a good book