Plunging into cold water during hot weather can cause heart attacks even in young, fit and healthy individuals, according to new research.
Scientists are warning that entering cold water suddenly, without taking time to acclimatise, may cause abnormal heart rhythms that can be fatal. The research comes after several people died after going into water during the recent heatwave, although the cause of death in these cases is not yet known.
Professor Mike Tipton, who runs the Extreme Environments Laboratory at the University of Portsmouth, said entering cold water should be done with caution. "As the recent sad spate of immersion deaths confirm, we have entered the most dangerous time of the year for water-related deaths," he said.
"As air temperatures rise dramatically, people start to go into water that remains dangerously cold. The body's responses to immersion in cold water are profound, uncontrollable and can result in drowning and heart problems within seconds."
In the study, published in the Journal of Physiology, Professor Tipton and Professor Mike Shattock, of King's College London, explain how rapid submersion in cold water, combined with holding your breath, automatically activates two powerful responses in the body which may interact and cause conflict for the heart.
The body's cold shock response speeds up the heart rate and causes hyperventilation which can conflict with its diving response, which does the opposite and acts to conserve oxygen. This can lead to "autonomic conflict", causing the heart to go into abnormal rhythms and, on occasions, causing sudden death.