KEY MESSAGES

• The sleep-wake cycle is controlled by specialised cells in the suprachiasmatic nucleus of the hypothalamus called circadian pacemakers, or body clocks.
• The master body clock in the hypothalamus is synchronised with peripheral body clocks in the organs, tissues, and cells to regulate physiological functions according to light-dark cycle of the circadian rhythm.
• Blood pressure (BP) variation over 24 hours follows a pattern, with a peak in the early morning and a decrease at night. This variation is the result of an endogenous circadian rhythm, which exerts its peak at around 9 pm, and of behavioural effects that are superimposed on the circadian pattern.
• Sleep disruption and circadian misalignment lead to immediate or long-term negative effects on health, including hypertension and cardiovascular diseases.