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.
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. 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.
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Most weather-related public health plans focus on heat waves, even though the death rate during cold spells exceeds that during heat waves.
One likely explanation is that cold is a stealth killer. Extremes of heat tend to kill quickly. 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, the overwhelming majority of cold-weather casualties are attributable to leading killers like heart disease, stroke and respiratory disease, and are especially common among those age 75 and older.
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.