Rising body temperature can cause brain damage and eventual death by effectively cooking cells. This process can start when the body reaches 40.5C. It causes only a few deaths each year in Britain, and those are usually caused by unusual activities, such as running in a wetsuit.
· Deaths from heart attack, stroke and coronary thrombosis can more than double on unexpectedly hot days, especially among the elderly and people with heart or respiratory problems. This combination of factors accounts for 800 deaths a year in Britain. It happens because we lose water through sweat which makes the blood stickier and more likely to clot, as well as increasing blood flow to the skin, which puts further pressure on the circulatory system.
· In hot weather, drink plenty of water. Grumpiness and an inability to think straight are early signs of dehydration. Avoid physical exertion and stay in the shade - continental Europeans have a daily siesta for a reason.