August 11, 2010 / 3:36 PM / 10 years ago

Rates of heart attack swell as temperature drops

NEW YORK (Reuters Health) - As the death toll of Moscow’s blistering heat continues to rise, British researchers said Wednesday that cold weather may exact a price, too.

They found that when temperatures dropped just one degree Celsius (1.8 Fahrenheit) on a given day, there were an additional 200 heart attacks in the UK over the next month.

Neither flu nor air pollution could explain the association, they report in the journal BMJ.

“As it gets colder, think about limiting the time outside,” said doctoral student Krishnan Bhaskaran, of the London School of Hygiene and Tropical Medicine, who worked on the study.

He said elderly people and those with heart disease were at highest risk and should pay extra attention to their clothing if they plan to spend time in wintry weather.

However, those who took aspirin, often used to prevent heart disease and strokes, had a lower risk.

It’s not clear from the data how lower temperatures would trigger heart attacks. Lab studies have suggested that cooling could increase blood clotting and make the blood thicker, or increase blood pressure. But in principle, the explanation could be as prosaic as snow shoveling, the researchers write.

Based on hospital records for more than 84,000 people who had suffered heart attacks, they calculated that every one-degree temperature drop on a given day was linked to a two percent risk increase over the next month.

That’s a small increase, but with about 146,000 heart attacks every year in the UK, just a few degrees of cold would mean several hundred extra cases.

Although earlier studies have shown that extreme heat and cold both have negative impacts on health, hot weather had no effect on heart attacks among Britons. One possible reason is that British temperatures, even on a hot summer day, simply aren’t high enough to make a difference, Bhaskaran said.

Whether the results would hold across the globe is unclear.

“In the U.S., we find that there is an optimal temperature where you have the lowest mortality, somewhere around 70 degrees Fahrenheit,” Dr. Jonathan Patz, a professor at the University of Wisconsin-Madison, who was not involved in the new research, told Reuters Health.

Compared to cold snaps, he said, heat takes a much larger toll on our health. Apart from dehydrating us, it forces the heart to work harder to get the blood to the skin for sweating. That can lead to heart failure in sick people or those who are old and frail.

With climate change, weather conditions will have an increasingly negative impact on our health, Patz said.

Although some places might see milder winters, “that benefit will be far outweighed by the increases in heat waves, droughts and pollution,” he said.

In the end, Bhaskaran said, “we can’t control the weather, but we can control our response to it.”

SOURCE: BMJ, online August 11, 2010.

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