Death rate climbs with summer heat

The long, hot days of July and August should come with a public health warning, say researchers who have identified a startling increase in death rates during hot snaps such as the sweltering summer of 1976. Even a moderate rise in temperature, above 19C (66F), can produce a substantial effect.

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The long, hot days of July and August should come with a public health warning, say researchers who have identified a startling increase in death rates during hot snaps such as the sweltering summer of 1976. Even a moderate rise in temperature, above 19C (66F), can produce a substantial effect.

Researchers from the London School of Hygiene and Tropical Medicine compared temperature readings in central London with death rates for 20 years from 1976 to 1996.

The biggest increase was in the 15-day heatwave in July and August 1976, when the extra deaths were twice those during any other hot spell.

The researchers found that, on average, when temperatures topped 21.5C the death rate increased 3.3 per cent for every degree rise. But in 1976 the average increase in the death rate was 4.7 per cent for every degree. Hot days in May or June appeared to have a greater impact than hot days later, though the highest average temperatures were in July and August.

Researchers believe people need time to acclimatise to the heat so by July and August they are less vulnerable.

The report, in the Journal of Epidemiology and Community Health, says it may also be the "harvesting phenomenon", where clusters of susceptible people die sooner than would be expected, followed by a drop-off in the death rate later as the pool of people at risk diminishes.

The effects of temperature rises are immediate, with the death toll dropping three days later. Elderly people and those with respiratory disease are the most vulnerable.

But, the authors add, cold weather claims more lives than hot.