Calgary chinook study shows no link between weather, stroke

Researchers in Calgary compared weather data to hospital records for stroke patients and found no link, challenging earlier reports.

A new Canadian study challenges earlier reports of a link between stroke and weather. It found no link between chinook winds and strokes.

Calgary was the ideal place to test the link. In the winter, geological and atmospheric factors in the city often cause chinooks rapid and extreme weather variations.

Chinooks can quickly raise the temperature in Calgary from -20 C to +10 in a matter of hours.

A team of researchers led by neurologist Dr. Michael Hill of the University of Calgary compared Environment Canada's hourly weather data from 1996 through 2000 to hospital discharge records for stroke patients in the city.

The researchers compared mean daily temperature, relative humidity, barometric pressure, and wind speed on chinook days to non-chinook days.

After tracking 182 chinook days and more than 3,000 strokes, they didn't see a pattern for any type of stroke.

"We found no association between weather changes and stroke occurrence," the researchers concluded in their study, which appears in the July issue of Stroke: Journal of the American Heart Association.

"A cause-and-effect relationship between weather and stroke occurrence is dubious because of a lack of consistency across studies."

Hill said earlier reports may not have considered variables such as culture, and a potential bias may have prevented negative studies from being published.

Outlook unclear

Stroke researcher Dr. Myles Conner of the University of Witwatersrand in Johannesburg, South Africa wrote an editorial that accompanies the study.

Conner said if there is a relationship between weather and stroke, it remains foggy.

Conner argues that because the study looked back over records, the researchers may have missed cases that were misdiagnosed, or people who were killed by their strokes and never made it to hospital.

Hill doubts these cases would sway the statistics, but he does believe the earlier studies may have been on to a link. He thinks an influenza-stroke connection could be at work, and he and his colleagues plan to cross-reference that data next.