A landmark five-year epidemiological study from the University of Pretoria used death data from Statistics SA and information from the SA Weather Service to investigate the association between daily ambient temperature and daily all cause non-accidental mortality in the three major cities. File Picture: Mohd Rasfan/AFP
Johannesburg - South Africans 65 or older living in Cape Town, Durban and Joburg faced a “significant increase in mortality” from increased daily ambient apparent temperature - a combination of humidity and temperature.

This is among the findings of a landmark five-year epidemiological study from the University of Pretoria (UP), which used death data from Statistics SA and information from the SA Weather Service, to investigate the association between daily ambient temperature and daily all cause non-accidental mortality in the three major cities. It’s the first study of its kind in Africa.

“Due to climate change, an increase of 3°C to 4°C in ambient temperature is projected along the South African coast and 6°C to 7°C inland during the next 80 years,” writes the paper’s author, Janine Wichmann, associate professor of environmental health at the school of health systems and public health.

“It’s this likelihood of higher temperatures under climate change in South Africa that highlights the need to elucidate how the population responds to ambient temperature.”

The results suggest that the general population has an increased risk of mortality with increasing daily ambient apparent temperature above city specific thresholds. For the study, the city specific daily ambient apparent temperature thresholds were set at 18.6 degrees for Cape Town, 24.8 degrees for Durban and 18.7 degrees for Joburg.

Cape Town has a Mediterranean climate; Durban has a humid subtropical climate, which borders on a tropical wet and dry climate; while Joburg has a subtropical highland climate.

Wichmann found an overall significant increase of 0.9% in mortality per one degree increase in daily ambient apparent temperature observed for all age groups combined in the three cities.

The elderly were more at risk. “For the plus-65 year age group, a significant increase of 2.1% in mortality was observed

“Physiological responses to variable ambient temperatures decline with ageing, such as reduced ability to maintain core temperature, reduced sweat gland output, reduced skin blood flow, smaller increase in cardiac output

“The elderly are also more likely to take medication that may interfere with an already weak thermoregulation Additionally mental disorders, such as dementia, also alter risk perception and protective behaviours. Social factors, such as living alone, living in nursing homes or being confined to bed also add to the increased risk.”

The study, Heat effects of ambient apparent temperature on all-cause mortality in Cape Town, Durban and Joburg for 2006-2010, found the risk for all age groups combined and the elderly are similar to those reported in studies from developed and developing countries.

Increased blood viscosity from dehydration, elevated cholesterol levels and a higher sweating threshold in the elderly may trigger heat-related mortality in susceptible individuals.

Few studies of this nature have been conducted in developing countries and “even fewer in Africa,” Wichmann points out.

“Detailed exposure assessments need to be conducted in cities in urban and rural areas for man years. Mortality data also needs to include the neighbourhood where the person lived, so one can assume the temperature observed in the neighbourhood is what the person was exposed to mostly prior to death, unless it’s clearly stated the person died in another town, city or province.”

Saturday Star