Why does the West have more deaths from cold exposure?
Drawing a line for the West to include the states Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming, the US Centers for Disease Control and Prevention (CDC) data indicate that, for nonmetropolitan areas:
- The West has 20.5 deaths per million population
- Other regions of the US have 4.5 to 7.8 deaths per million.
The data for the analysis come from the US National Vital Statistics System, and compared with those rural figures, "cold deaths" are lower in metropolitan areas across the US, ranging from 2.9 to 5.0 per million population.
The deaths recorded as having causes related to exposure to the cold, for the years 2002-13, are age-adjusted figures - they take account of any weighting towards higher numbers of deaths that might have been explained by greater numbers of older people in a region.
The list below of nonmetropolitan death rates versus metropolitan (per million people) shows that rates are higher in nonmetropolitan areas across the US and that there is a rural disparity in the West:
- 4.8 vs. 2.8 in the South
- 7.2 vs. 3.8 in the North-East
- 7.3 vs. 4.8 in the Mid-West
- 18.0 vs. 3.4 in the West.
A report from The BMJ analyzes the data and is accompanied by an infographic that reveals the data by region and state with each mouse click.
As this diagram from The BMJ shows, rural areas of the West produce the biggest bar of CDC data on deaths due to the cold.
Image credit: Will Stahl-Timmins/The BMJ
Selecting the data for the most recent periods also suggests the rural cold phenomenon in the West has been rising - the figure for the years 2002-05 was 15.3 deaths due to cold in every 1,000,000 population, rising to 19.2 in the middle period, and remaining at 19.3 for 2010-13.
The BMJ says in a press release that it is "unclear why the people living in the rural West were at higher risk," but cites research on weather-related deaths that indicates an increased risk due to the cold for people who live at high elevations or in places with:
- Temperature shifts that happen rapidly
- Night-time temperatures that shift by a large amount.
Using the infographic to click on the West pops out the individual states - and its coastal states fare best on cold-related death rates.
The three Pacific-facing states of California, Oregon and Washington show, for rural deaths, the clearly lowest rates across the whole study period, with low figures for metropolitan areas, too.
Alaska, Arizona and New Mexico, meanwhile, fare worst overall - they show the clear highest rates of death due to the cold in the West, both in the rural figure alone and in the figure combining metropolitan areas. Montana also showed high figures, peaking in the middle period.
Arizona shows the biggest differential between rural and metropolitan areas for cold-related deaths.
How does exposure to the cold cause death?
The CDC data come from records of death in which the cause attributed was exposure to excessive cold - whether as an underlying or contributing cause.
The specific causes of death included come from the International Classification of Diseases (ICD). They were:
- Deaths attributed to exposure to excessive natural cold (ICD code X31), whether underlying or contributing cause of death
- Hypothermia (T68), contributing cause
- Effect of reduced temperature, unspecified (T69.9), contributing cause
- Or any combination of the above.
The 2014 CDC report on weather-related deaths that might offer an explanation for the West's phenomenon in terms of living at higher altitudes and seeing bigger or more rapid temperature changes also lists a number of factors affecting the population in general.
Exposure to extreme natural cold can itself lead to hypothermia, which may result in death, but it can also pick out more vulnerable people. The report lists:
- Those with pre-existing chronic conditions (including cardiovascular and respiratory diseases)
- People with conditions that impair their bodies' ability to regulatory temperature (thermoregulatory function)
- Those taking various medications are more susceptible to cold effects.
The report also notes evidence that cold weather particularly affects certain groups of people in the same way that extremely hot weather does. As well as vulnerable older people, these at-risk groups include:
"Alcoholics, persons taking recreational drugs (especially alcohol), homeless persons, those with inadequate winter clothing or home heating, those who go on wilderness excursions, and those who participate in winter sports also are at increased risk of cold-related mortality."