Sleep and cognition

Why sleep matters for the brain

The brain consolidates memories, clears metabolic waste, and regulates emotion during sleep. The glymphatic system, which removes amyloid and other waste products, is most active during deep sleep. Untreated sleep disorders accelerate cognitive decline and probably contribute to dementia risk.

Sleep changes with age

Several changes are normal:

• Reduced total sleep time (7 hours rather than 8);
• Less deep sleep;
• More frequent night-time waking;
• Earlier wake time and earlier evening tiredness.

What is not normal: severe insomnia, daytime sleepiness, witnessed apnoeas, snoring with apnoeas, and acting out dreams.

Obstructive Sleep Apnoea

Obstructive Sleep Apnoea is common in older adults and frequently missed. Untreated OSA roughly doubles dementia risk. Suggestive features:

• Loud snoring;
• Witnessed apnoeas (pauses in breathing);
• Excessive daytime sleepiness;
• Morning headache;
• Reduced concentration;
• Low mood;
• Treatment-resistant Hypertension.

If suspected, ask your GP for referral to a sleep service. A home or laboratory sleep study confirms the diagnosis. Treatment with Continuous Positive Airway Pressure (CPAP) is effective and substantially improves daytime cognition. Mandibular advancement devices and positional therapy are alternatives in milder cases.

Chronic insomnia

Persistent difficulty falling asleep, staying asleep or early waking, with daytime consequences. UK NICE recommends:

• Sleep hygiene and behavioural advice as first line;
• Cognitive Behavioural Therapy for Insomnia (CBT-I) as the most effective long-term treatment;
• Short-term medication only where other approaches have failed.

Sleep hygiene

• Wake at the same time daily;
• Morning bright light exposure;
• Limit daytime naps (under 30 minutes, not after 3 pm);
• Daytime physical activity;
• No caffeine after midday;
• Alcohol moderation;
• Dinner two to three hours before bed;
• Cool, dark, quiet bedroom;
• Bed for sleep and intimacy only;
• Wind down with dim lights in the hour before bed.

Cognitive Behavioural Therapy for Insomnia

CBT-I is the gold standard treatment for chronic insomnia. It includes:

• Stimulus control (only go to bed when sleepy, get up if not asleep within 20 minutes);
• Sleep restriction (limit time in bed to match actual sleep, then gradually extend);
• Cognitive techniques for worry and rumination;
• Relaxation training.

Available through NHS Talking Therapies (England, formerly IAPT), apps such as Sleepio (some areas via NHS), and private CBT-I therapists.

Medication for sleep

Most sleep medications worsen cognition and increase falls in older adults:

• Benzodiazepines (Diazepam, Temazepam): avoid routinely;
• Z-drugs (Zopiclone, Zolpidem): avoid routinely;
• Sedating antihistamines (Promethazine): worsen cognition through anticholinergic burden;
• Melatonin: licensed in the UK for primary insomnia in adults 55 and over (2 mg prolonged release); well tolerated;
• Low-dose Trazodone or Mirtazapine: sometimes used where mood symptoms coexist.

Medication is a short-term option while CBT-I or other approaches take effect.

Sleep in dementia

See sleep disturbance for the specific sleep problems of dementia: insomnia, day-night reversal, sundowning, and REM Sleep Behaviour Disorder.