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High BP + Cold Weather Ups Heart Attack Risk

Risk Doubles When Temperature Drops Below 25 Degrees
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WebMD Health News

Aug. 31, 2004 (Munich, Germany) -- High blood pressure is a well-known risk factor for heart disease and stroke, but new research suggests that the risk attributed to high blood pressure goes up as the temperature goes down.

Researchers in France report that for those with high blood pressure -- meaning a pressure higher than 140/90 -- the risk of heart attack doubles when the temperature drops to less than 25 degrees Fahrenheit or 4 degrees Celsius.

The researchers, Yves Cotton, MD, and Marianne Zeller, MD, of the University of Dijon, analyzed data from more than 700 people who were admitted to the hospital with heart attacks during a two-year period. Roughly half of the heart attack patients were being treated for high blood pressure at the time of the heart attack or had a history of high blood pressure.

When the researchers cross-referenced the timing of the attacks with weather records during the same two-year period, they discovered that not only were heart attacks more common during cold spells, but that sudden weather changes from the day before to the day of the heart attack -- such as drops of 5 or more degrees in a single day -- also the spiked increases in heart attacks in people with high blood pressure.

These sudden weather changes were associated with a more than 60% increase in risk in people with high blood pressure, according to the researchers.

Narrower Vessels, Thicker Blood

Asked about the high blood pressure-cold weather link, Rose Marie Robertson, MD, chief science officer at the American Heart Association (AHA), tells WebMD, "Cold weather makes the blood vessels constrict, and when vessels constrict, pressure goes up. So if a person already has high blood pressure, this extra constriction could trigger an event."

David Faxon, MD, a former AHA president and a professor of cardiology at the University of Chicago, agrees that the weather link makes sense. He notes that a medical test called "cold pressor" measures changes in blood pressure after a person's arm is plunged into ice cold water for 45 seconds. "So I agree that there is some logic here," he says.

Cottin and Zeller, who presented their findings at the 2004 European Society of Cardiology meeting, say that cold also makes blood more viscous -- thicker and stickier -- which may cause clots to form. Those clots, they say, can block blood flow to the arteries in the heart and cause heart attacks. Additionally, they say that cholesterol also goes up during cold weather and the number of respiratory infections also increases, which "might contribute to respiratory difficulties that also may contribute to heart attack risk."

But Robertson says that the real point of the study is not "that people with high blood pressure should avoid cold weather. Rather, the message is pretty clear: If you have high blood pressure, it needs to be treated and controlled." With proper management, blood pressure can be maintained at safe levels, which would mean that a walk in snowy weather would not put one's heart at risk.

Robertson adds that optimal blood pressure is 120/80.

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