Heart rate increases by about 10 beats per minute with every degree of increased body temperature. Normally, sleep is when the body recovers; heart rate slows, blood pressure drops and the parasympathetic nervous system – the ‘rest and digest’ mode – takes over. The new study found that when nighttime bedroom temperatures exceeded 75 degrees, older adults’ nervous systems remained stuck in a higher-alert state. Heart rate increased and heart rate variability, a key marker of recovery, dropped. The combination of increased heart rate, sympathetic nervous system takeover and reduced heart rate variability, a marker of poor recovery, deprives the cardiovascular system of its overnight rest period.

Source: Daily Mail February 23, 2026 18:48 UTC