By Tim Radford
Australian and Chinese scientists have identified a new hazard in the summer heat waves – more undernourished and hungry people are driven into hospitals.
They combed the records of Brazil’s hospitals, matched them against temperature readings and found that for every 1°C increase in temperature, there was a 2.5% increase in hospital admissions for undernutrition.
Undernutrition is defined as “inadequate intake of energy and nutrients to meet an individual’s needs to maintain good health.” That is: with extremes of heat come the ravages of hunger. The researchers also found that the very young and the very old were the most vulnerable.
Undernutrition is a global public health concern, especially in the low- and middle-income nations. In 2016, around 420 million adults of 20 years and more, and 192 million children and adolescents between 5 and 19, were underweight.
Of children under 5 years of age, 150 million were stunted, and 52 million were wasted. Around 45% of deaths of children under 5 were associated with undernutrition.
“The malnourished are more often from the poorest communities: they cannot stay indoors with the air-conditioning switched on”
And now the climate emergency, which brings with it ever greater extremes of heat, could make a global problem even worse.
Quite how dangerous heat and dangerous hunger are linked is uncertain, but the researchers report in the Public Library of Science journal PLOS Medicine that they have confirmed that the link is a real one.
Yuming Guo of Monash University in Australia and colleagues gathered data from the 5,570 cities in Brazil’s unified health system from January 2000 to December 2015. However, they included data only from the 1,814 cities – with more than 78% of Brazil’s population, in five regions – that could produce 16 complete years of records.
They had already established that hospital admissions rose with the thermometer. This time they established that one in six of the hospitalisations for undernutrition – that is, 37,129 cases – could be attributed to heat exposure. This proportion had risen from 14% in 2000 to 17.5% in 2015, during which time average temperatures rose by 1.1°C.
Spreading heat extremes
The links between heat and health have been repeatedly confirmed. Heat extremes, driven by global average temperature rises, in turn powered by profligate fossil fuel use, are on the increase: by the end of the century, they will be more intense, more frequent and more prolonged. And by the end of the century, three-fourths of the world could be at potentially lethal risk from the baking days and sweltering nights.
Researchers have repeatedly established that extremes of heat can affect harvest yields, and that high growing season temperatures, driven by ever higher levels of atmospheric carbon dioxide, can reduce protein and vital nutrient levels in crops, to amplify global hunger and malnourishment. One research group even catalogued 27 ways in which heat extremes could kill.
These are long-term consequences. What the latest study does is put a measure to the short-term effect of heat upon illness linked to undernourishment. How the connection works is – the scientists concede – “not well understood.”
They suggest that high temperatures could reduce appetites, provoke more alcohol consumption, or reduce motivation to shop and cook, which would make any existing under-nutrition even worse. They also think that the sweltering heat could worsen already-impaired digestion and increase the frequencies of gastroenteritis.
Less healthy targeted
And, of course, those already undernourished are less healthy and less able to naturally regulate their own body temperatures. Finally, the malnourished are more often from the poorest communities: they cannot stay indoors with the air-conditioning switched on.
There could be many factors. But one thing is clear: heatwaves most harm those already less healthy because of undernutrition. By 2050, climate change could reduce global food supplies by more than 3% and cause around 30,000 underweight-related deaths.
But, the researchers warn, this now looks like an under-estimate, because it does not take into account the short-term and direct effects of temperature rise on future undernutrition-related morbidity and mortality.
“This direct, short-term effect will be increasingly important with global warning,” the scientists warn.