A new study suggests that heart attacks occur more often when temperatures plummet. According to the report in JAMA Cardiology, based on more than 15 years of medical and weather data, researchers linked an increased incidence of heart attacks to lower air temperatures, lower atmospheric pressure, higher wind velocity and shorter time spent in the sunshine.
Its senior author said that "all heart attacks occurring in an entire country have been followed for 16 years with weather data for the day the heart attack occurred."
Dr. David Erlinge, head of cardiology at Lund University and Skane University Hospital in Sweden, told Reuters Health: "We had data on more than 280,000 heart attacks and 3 million weather data points."
Erlinge and his colleagues pored over records from the SWEDEHEART registry, which enrolls all consecutive patients in Sweden with symptoms suggestive of a heart attack who are admitted to a coronary intensive care unit or a coronary catheterization lab.
The registry contains a wealth of health information on patients, including age, body mass, smoking status, echocardiogram findings, interventions, discharge medications and diagnoses.
For meteorological data, the researchers turned to the SMHI, a Swedish government agency that registers data from 132 weather stations across the nation.
Erlinge and colleagues analyzed the weather and heart attack data from 1998 through 2013 for 274,029 patients, half of whom were aged 71 or older.
While lower air temperature, lower atmospheric air pressure, higher wind velocity and shorter sunshine duration all were associated with statistically meaningful increased risk of heart attack, the most pronounced effect was from temperature.
The researchers found a higher incidence of heart attack on days with air temperatures below freezing. The rates of heart attack declined when temperatures rose to more than 3 to 4 degrees Celsius. So, why would cold temperatures raise the risk of heart attack?
Dr. Nisha Jhalani of the Center for Interventional Vascular Therapy in New York City said: "Colder temperatures increase vasoconstriction in the arteries which causes them to clamp down. In someone with 70 to 80 percent blocked arteries, which might not be causing any symptoms normally, the arteries can be clamped down enough that the blood supply doesn’t match demand.”
There are other factors related to winter that can increase the risk of heart attacks, such as shoveling snow, which raises blood pressure to levels that could disturb vulnerable plaques, Jhalani said. Caffeine has a similar clamping down effect on arteries, albeit a lot smaller.
"So the worst thing you can do is go out in subzero temperatures, shovel snow and then come in and drink coffee to warm up," she said.
