How cold kills

We know from simple observed data that cold is deadly: when temperatures go down, death rates go up. But how does cold kill people?

As temperatures go down, death rates go up. Daniel L. Baker E. and Williamson T. (2018) Residential wintertime comfort in a temperate Australian climate. 10th Windsor Conference: Rethinking Thermal Comfort, April 2018, Network for Comfort and Energy Use in Buildings, 852-864.

In general, deaths are not from hypothermia - it’s not people ‘freezing to death’. (That said, Australia does have an alarmingly high rate of people getting hypothermia inside their own homes.)

Rather, the deaths happen as a consequence of ongoing exposure to ongoing, even fairly mild, cold.

About half of excess winter deaths are due to cardiovascular effects. When people get cold, their blood becomes more concentrated as the proportion of salt and water in the blood is reduced. This makes the blood more likely to clot, which can cause thrombosis, leading to, for example, a heart attack. Cold weather also causes blood vessels to constrict, which increases blood pressure and can contribute to stroke. For healthy young adults, this isn’t generally an issue - but for elderly people, it can be deadly.

Older Australians are more vulnerable to the health risks from cold homes.

Another factor is respiratory disease - causing about one quarter of excess winter deaths. This is partly due to outdoor cold, which means that people spend more time indoors, encouraging infection. But indoor cold plays a role too: inhaling cold air worsens the symptoms of colds, and colder weather leads to an increase in GP consultations for respiratory infections. Cold, damp housing also leads to mould, which causes childhood asthma and lowers resistance to infection.

In Yakutsk, the coldest city in the world, temperatures reach as low as -48ºC. Yet people there don’t suffer from an increase in mortality. In Australia, something is different, with people getting sick and dying more in colder weather. One difference is our homes. Reducing energy waste and requiring healthy homes will help keep Australians safe from the perils of indoor cold.