Most of the Northern Hemisphere is in the throes of the deadliest time of the year. Cold kills, and I don’t mean just extreme cold and crippling blizzards. I mean ordinary winter cold, like that typically experienced, chronically or episodically, by people in every state but Hawaii from late fall through early spring.
While casualties resulting from heat waves receive wide publicity, deaths from bouts of extreme cold rarely do, and those resulting from ordinary winter weather warrant virtually no attention. Yet an international study covering 384 locations in 13 countries, including the United States, found that cold weather is responsible, directly or indirectly, for 20 times more deaths than hot weather.
Over time, milder winter temperatures are likely to result in fewer cold-related deaths, a benefit that could outweigh a smaller rise in heat-caused mortality. In winter in the United States, mortality is generally 10 percent to 15 percent higher than on typical summer days.
The study, published in July 2015 in The Lancet, was based on an analysis of more than 74 million deaths and calculated mortality attributable to heat and cold in Australia, Brazil, Canada, China, Italy, Japan, South Korea, Spain, Sweden, Taiwan, Thailand, Britain and the United States.
The researchers found that extreme temperatures of heat or cold were responsible for less than 1 percent (0.86 percent) of total mortality. “Heat stroke on hot days and hypothermia on cold days only account for small proportions of excess deaths” related to temperature, the research team wrote.
Less extreme temperatures, on the other hand, contributed to many more deaths, with temperature playing a direct or indirect role in 7.71 percent of deaths overall. The vast majority of these “temperature-attributable deaths” (7.29 percent) occurred on days when temperatures were below the “optimum temperature” — the temperature in each country that is associated with the lowest death rate — whereas only 0.42 percent were associated with above optimum temperatures.
Yet most weather-related public health plans focus on heat waves, even though the death rate during cold spells exceeds that during heat waves, and minimal if any attention has been given to the life-threatening risks linked to everyday cold.
One likely explanation is that cold is a stealth killer. Extremes of heat tend to kill quickly, with spikes in deaths striking within days of a hot spell. But cold exacts a more protracted toll, with an increase in cold-related deaths occurring as long as three or four weeks after a cold snap.
Furthermore, unlike what you might expect, the overwhelming majority of cold-weather casualties do not result from vehicular accidents, falls on ice or snow-related activities. Rather, they are attributable to leading killers like heart disease, stroke and respiratory disease, and are especially common among those age 75 and older.
Writing in the Southern Medical Journal in 2004, W.R. Keatinge and G.C. Donaldson of Queen Mary’s School of Medicine and Dentistry at the University of London reported that “cold-related deaths are far more numerous than heat-related deaths” in nearly all countries outside the tropics, and “almost all of them are due to common illnesses that are increased by cold,” including heart attacks, strokes, flu and pneumonia. The authors added that “even in climates as warm as Southern Europe or North Carolina, cold weather causes more deaths than hot weather,” prompting them to suggest that “rising temperatures could reduce overall mortality rates.”
In other words, with respect to minimizing deaths everywhere but in the tropics, milder winters would save more lives and have a much greater impact on mortality than hotter summers.
Surprising though it may seem, people living in countries with relatively mild winters are more likely to succumb to the cold than those who reside where subfreezing temperatures are commonplace. In relatively cold Sweden, for example, cold contributed to an estimated 3.9 percent of deaths, while in warmer Australia it was responsible for 6.5 percent — one death in 15, according to the international study. It is not just a matter of adaptation. A more likely explanation: Swedish homes are better built and equipped to keep out the cold, and residents are more likely to have and wear appropriate winter attire.
An Australian blogger, Adrian Barnett, an associate professor of public health at Queensland University of Technology, wrote that in winter, “temperatures inside a flimsy wooden Queenslander” — the typical home in the region — “are often below 18°C,” or 64.4 degrees Fahrenheit, “whereas Swedish homes will be a comfortable 23°C,” or 73.4 degrees Fahrenheit, “whatever the weather. Many Australian homes are just glorified tents, and we expose ourselves to far colder temperatures than the Scandinavians do.” The same might be said for folks living in the southern United States, compared with those in the much colder Northeast.
How, you may wonder, does cold exact its deadly toll? About half of cold-related deaths result from blood clots that cause heart attacks and strokes, the British researchers reported. Blood becomes more concentrated during exposure to cold because blood flow to the skin is reduced to conserve body heat. This results in an excess of blood in the central parts of the body. To counter the excess volume, salt and water move from the blood into the tissue spaces, leaving behind “increased levels of red cells, white cells, platelets and fibrinogen” — thickened blood that is more likely to clot. Blood pressure, an important risk factor for heart attacks and strokes, also tends to rise with exposure to cold.
During cold weather, people typically spend more time indoors and congregate in smaller spaces. This helps to spread respiratory infections like cold, flu and pneumonia that can take a heavy toll among people with underlying chronic ailments like heart disease, chronic obstructive pulmonary disease, diabetes, asthma and even cancer and dementia.
Of course, the winter months have more than their fair share of accidental deaths. In addition to cardiac deaths among people middle-age and older who, like me, choose to shovel their own stoops and sidewalks, there are some who wind up in the morgue after a slip or skid on icy streets and roads or who crash a car in a blinding snowstorm.
There are also far more fire-related deaths in cold weather, resulting from faulty or overtaxed wiring, improper use of indoor heaters and errant sparks from fireplaces. With windows and doors closed and tightly sealed to keep out the cold, the risk of carbon monoxide death also rises.