Australasian Science: Australia's authority on science since 1938

Unexpected Cold a Killer

By Stephen Luntz

Perth and Sydney experience greater increases in cardiovascular death rates over winter than Tasmania does, a new study has found.

Dr Adrian Barnett of the Queensland Institute of Technology is not as surprised as the general public might be. “A lot of very large studies have found that Scandinavia has a much lower increase in winter deaths than Spain, Italy and Greece,” he says.

However, Barnett says that this could be affected by differences in wealth, culture or the quality of the health care system. “Australia’s a good place to study this because we have such a wide range of climates but relatively similar culture and socio-economic circumstances,” Barnett says.

It seems that Tasmanians, and to a lesser extent Melbournians, simply know how to deal with the cold. But people in Perth, Sydney and Brisbane are unprepared, so when the temperature drops below 19°C it can be enough to cause mortality rates to spike.

At such temperatures “we are very far from hyperthermia,” Barnett says, but the problem is that “the body likes to keep a stable temperature. When it gets cold, the veins beneath the skin shrink. This keeps the blood warmer but also raises its pressure. What’s more, if you have a partial blockage in the veins, and they shrink, that becomes more of a problem.”

Cold temperatures can also cause an increase in deaths from respiratory disease, but Barnett says that the factors here are different and he didn’t consider those deaths.

Barnett says he has applied several times for funding to investigate whether the major problem relates to housing design or failure to wear adequate clothing. “The further north you go, the more houses are designed to keep out heat. If you’re in a house on stilts with thin floors it gets cold in winter very easily,” he says. On the other hand, “putting on a hat and gloves” might be enough to prevent a lot of the extra deaths.

So far Barnett’s efforts to discover the relative importance of these factors have not received research funding. He suspects “it’s a bit of both”.

With cardiovascular death rates in July more than one-third higher than January, cold is clearly a major killer but Barnett notes: “Most of the people who die are probably already frail or have a pre-existing condition”. After a particularly severe winter, the following winter tends to cause fewer deaths, while mortality rates are higher in the year after a mild season.

Factors such as humidity appear to be minor contributors to deaths relative to temperature alone.