During his lifetime, author and broadcaster Michael Mosley was a tireless health educator. His tragic death while on holiday in Greece has been a reminder of one more important lesson. Heatwaves can be lethal.
Mosley, 67, is believed to have collapsed after becoming lost while out walking in the heat of the day on the island of Symi. Temperatures had reached 37⁰C and may have been up to 10֯C hotter on the higher rugged and rocky ground that he was walking over.
As the Northern Hemisphere summer sees temperatures soar, other tourists have died from the heat. In Saudi Arabia, more than 1300 people were reported to have died on the annual hajj pilgrimage to Mecca, walking in over 50⁰C temperatures. It is estimated that, every year, more than 150,000 deaths around the globe are associated with extreme heat.
While the human body does have a cooling system, it can only cope with so much. The cardiovascular system is put under particular strain. Elevated temperatures trigger vasodilation, widening blood vessels to dissipate heat, which means the heart has to work harder to maintain blood flow.
Also, we sweat as part of our bodies’ cooling strategy but that can lead to dehydration which causes the blood to thicken, putting even more strain on the heart and increasing the chance of clotting. Excessive sweating alters the balance of electrolytes in body fluids, which can affect nerve and muscle function. In extreme cases, this can result in seizures, breathing difficulties or heart muscle spasms, which can be fatal.
Prolonged physical activity on a hot day is obviously risky but even resting in the heat puts extra stress on the heart, according to a recent study by scientists at the University of Sydney and the Montreal Heart Institute.
In a laboratory experiment, they exposed 61 participants to heat until their core temperature had risen by 1.5⁰C. Researchers monitored participants’ hearts and found everyone’s heart had to work harder. Seven older adults who suffered from coronary heart disease had heat-induced myocardial ischemia (lack of blood flow to the heart).
Anyone with a chronic condition is at greater risk of hospitalisation during extremely hot weather. As well as cardiovascular disease, these conditions include diabetes, asthma/COPD and chronic kidney disease. The more diseases a person has, the more chance they will need medical care on hot days, with the risk of a heart attack significantly higher during heatwaves.
Every organ in the body is affected by extreme heat, including the brain. During a heatwave in 2016, a Harvard researcher Jose Guillermo Cedeño Laurent had a group of healthy young students perform maths and self-control tests. Those who were sleeping in dorms with no air-conditioning performed significantly worse each morning than the luckier students whose rooms were cool. Other studies in laboratory settings have produced similar results with even relatively small increases in heat leading to a drop in cognitive performance.
Confusion is one of the signs of heat exhaustion. Dizziness, muscle cramps, fever, fatigue, nausea and vomiting are also key symptoms. It is vital to get to a cool place and rehydrate to avoid progression to the even more serious heatstroke which can cause brain damage, organ failure and can quickly prove fatal without emergency treatment.
Some people are particularly vulnerable to hot temperatures including the elderly, small children, pregnant women and people on common medications used to treat high blood pressure, allergies and mental health conditions.
But anyone heading to a hot destination should be mindful of the challenges heat can bring, especially when temperatures stay high for days at a time, says Dr Cheryl Brunton, Medical Officer of Health at Te Whatu Ora. She advises staying inside during the hottest part of the day, drinking plenty of water, avoiding caffeine, alcohol and extreme physical exertion.
“It’s important that people exposed to hot weather for long periods of time carry water with them and sip at least half a litre an hour,” adds Brunton.
