DALLAS, Oct. 12 -- Deaths from heart attacks appear to be seasonal, peaking during the winter holiday season of December and January and then falling, researchers report in today's Circulation: Journal of the American Heart Association.
Past studies have shown that deaths from heart attacks are more likely to occur during the early morning waking hours, but fewer studies have related coronary deaths to the months and the seasons.
When University of Southern California researchers looked at deaths from coronary artery disease for a 12-year period in Los Angeles, they found there were 33 percent more deaths in the holiday season of December and January compared to the summer and early fall.
"We were surprised by that," says Robert A. Kloner, M.D., Ph.D., director of research at The Heart Institute, Good Samaritan Hospital, Los Angeles and professor of medicine, University of Southern California, Los Angeles. "We weren't expecting that much of a difference."
Kloner says a few previous studies have shown that deaths from heart disease climbed as the temperature dropped. But in sunny, southern California where the temperature usually only fluctuates from 50 to 80 degrees, the researchers weren't expecting such an increase in the winter.
One explanation may be the holiday season, says Kloner. "The death rates are relatively steady through November then shoot up after Thanksgiving and through Christmas, peaking around the first of the year. This could be due to increased food, alcohol and salt consumption and increased stress during the holidays.
"Individuals may not be able to control the weather, but it may help to cut down on high-fat foods during the holidays," he adds.
Another possible factor could be the increased use of fireplaces and the particles emitted into the air from burning wood. These particles might irritate the lungs, decreasing the amount of oxygen in the bloodstream and then placing stress on the heart, says Kloner. It is clear that temperature doesn't explain everything, he says. "The higher coronary death rate during the winter months appears to be due to a combination of factors."
"Clearly some of these factors are environmental," says Kloner. "The more we understand about the factors that result in death from coronary disease the better we can treat them in the future."
The researchers studied 222,265 death certificates from the Los Angeles County's Department of Health Services Data Collection and Analysis Unit for deaths from coronary artery disease between 1985 through 1996. The average monthly number of deaths resulting from coronary artery disease was then averaged over 12 years. The number of deaths was highest in December with an average 1,808 deaths and January with 1,925 deaths. The lowest occurred in June with 1,402 deaths, July with 1,424 deaths, August with 1,418 deaths and September with 1,371 deaths. The good news, according to Kloner, is that there appeared to be an overall reduction in the deaths over the 12-year period of 16 percent. "This is probably due to better therapies and better lifestyles and risk modification by individuals," he says.
However, when deaths did occur, the researchers discovered they tended to have a rapid rise right after Thanksgiving, continuing through Christmas and peaking around New Year's Day.
Researchers found little correlation between the average daily temperature, because the day-to-day temperature fluctuations were minimal. However, there did appear to be a relationship between cooler temperatures and coronary deaths when calculated on a monthly basis. Researchers say this could be due to an increased workload on the heart during the winter, higher blood pressure and higher fibrinogen, a clotting protein that is associated with an increase in heart attack risk.
But since the temperatures are so mild in Los Angeles, Kloner believes there are other contributing factors as well. One is the increase in respiratory infections during the winter, which could play a role. Other researchers include Kenneth Poole, Ph.D., scientist and statistician, and Rebecca Perritt, MS, statistician, both of the Research Triangle Institute, Research Triangle, NC.