Key takeaways

•       Habitual sleep duration under 7 hours is robustly associated with worse outcomes across metabolic, cardiovascular, immune, cognitive, and mental health domains.

•       Short sleep disrupts appetite-regulating hormones, reducing insulin sensitivity and increasing risk of type 2 diabetes and obesity.

•       Cardiovascular risk is elevated by chronically short or fragmented sleep, via sustained blood pressure elevation and increased systemic inflammation.

•       Sleep plays an active role in immune defence and vaccine response; short sleepers are more susceptible to infection.

•       The brain’s glymphatic waste-clearance system operates primarily during sleep; chronic sleep insufficiency may impair clearance of proteins associated with Alzheimer’s disease.

•       Chronic insomnia is bidirectionally linked with depression and anxiety; CBT-I is the NICE-recommended first-line treatment.

•       Effects are systemic and cumulative. Sleep is most usefully treated as a health behaviour on a par with diet and exercise, not as a passive default state.