Cold exposure, not influenza, major cause of excess winter mortality

By Karla Gale

LONDON (Reuters Health) – The notion that becoming chilled can make you sick is no old wives' tale, investigators in the UK report. They found that compared with influenza cold stress is actually responsible for much more of the excess mortality rate observed during winter months.

"In Europe, we've found a linear increase in mortality as the temperature declines from 18 degrees Celsius," Dr. William R. Keatinge told Reuters Health. "Excess deaths during cold weather in Britain are around 50,000 every year–so this is a big cause of premature death."

Drs. Keatinge and G. C. Donaldson, of Queen Mary and Westfield College in London, recorded the number of deaths attributed to all causes and to influenza that occurred between 1970 and 1999 in southeast England. They also documented the daily mean temperature at Heathrow Airport. They describe their data analysis in the January 12th issue of the British Medical Journal.

Annual death rates related to influenza averaged only 2.4% of the 1265 annual excess winter deaths per million, the researchers calculated.

"In Europe, our findings have been very paradoxical," Dr. Keatinge said. "For those who live in eastern Siberia, where climate is the coldest, there is no excess mortality in winter. Those residents are better equipped to deal with the cold, wearing appropriate clothing when outdoors and avoiding excess exposure."

"In places like London and Athens, people tend not to take precautions against the cold," he continued. "People don't like to be 'pushed around' by the weather," he said. For example, people will wait for buses for long periods, while being totally exposed to the wind.

Dr. Keatinge noted that when there is moderate wind, even at temperatures as high as 5 degrees Celsius, a person's blood will undergo major changes in composition over 20 minutes to half an hour.

"Blood will become thicker and stickier," he said, increasing the chances of clotting, subsequent myocardial infarction, or respiratory infection.

The problem is age-related, with very little threat for those under age 50 to 55 years, he noted. After that, however, "the excess winter death rate goes up sharply, because these individuals are likely to have atheroma, and when the blood gets sticky they are at risk of clot formation."

Dr. Keatinge recommends that physicians advise their older patients to bundle up well when going out into the cold, to avoid prolonged exposure, and to find protection from the wind.

BMJ 2002;324:89-90.

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