Why more heart-related deaths happen around the holidays

June 7, 2012: Actress and screenwriter Carrie Fisher waves after speaking in tribute at the TV Land cable channel taping of the AFI Life Achievement Award honoring actress Shirley MacLaine. (Reuters)

Deaths from heart-related causes tend to spike around the holidays, and the cold weather may not really be to blame, a recent study suggests.

To rule out the potential influence of freezing temperatures, researchers examined data on more than 738,000 deaths from 1988 to 2013 in New Zealand, where Christmas comes during the summer. Overall, about 197,000 of these fatalities were heart-related.

Outside of the hospital, there were 4.2 percent more heart-related deaths during the last week of December and the first week of January - the period encompassing Christmas and New Year's Eve - than would be expected if the holidays didn't affect death rates, the study found.

The mortality rate works out to about an extra four deaths per year attributable to the holidays. The average age at the time of death was also slightly younger during the holiday season - 76.2 - compared with 77.1 during other times of year.

"This strongly suggests that the Christmas effect isn't caused by temperature or anything related to the winter season," said lead study author Dr. John Knight of the University of Melbourne in Australia.

"When temperature is removed as a likely cause that leaves a reasonably small pool of established social, health and health-system-related risk factors," Knight added by email.

Previous research has documented a spike in deaths from natural causes during the holiday season in the United States, where Christmas tends to fall during the coldest time of year and death rates are already seasonally high due to influenza, researchers note in the Journal of the American Heart Association.

For the current study, researchers analyzed death trends in New Zealand, where cardiac death rates tend to be lowest during the summertime in general.

The study is observational, and doesn't prove the holidays or the weather directly cause an uptick in fatalities or heart-related deaths, the authors note.

Researchers also didn't track daily temperatures in New Zealand, which has an island climate without extreme swings in hot and cold weather that have been associated with heart-related deaths in other studies.

It's possible, though, that heart-related deaths during the holiday season might spike due to seasonal stress, changes in diet and alcohol consumption or lower staffing at hospitals, the authors speculate.

At least some of the increase in cardiac deaths around the holidays might also occur because people put off needed care during this time of year or avoid seeking treatment for acute illness because they're traveling away from home, the researchers also point out.

Some terminally ill patients also may manage to hold off dying until just after they get through one last Christmas with friends or loved ones, the authors conclude.

In particular, other research has documented a link between excessive drinking and a greater likelihood that people will develop or need treatment for heart problems, said Dr. Tim Stockwell, a researcher at the University of Victoria in British Columbia who wasn't involved in the study.

"Many other factors have been speculated about as contributing to the phenomenon of more cardiac deaths at holiday periods, e.g. more respiratory infections because of cold weather at Christmas time, less accessibility to health care, increased stress," Stockwell said by email.

"This new study is able to rule out the cold weather hypothesis as the sole cause since the study looked at the Christmas holiday in New Zealand which falls in the summer," Stockwell added. "There was some support for the theory that there is less access to healthcare during the holiday due to the effect being more pronounced for deaths occurring outside of hospital, and increased emotional stress, dietary changes and additional stress are also consistent with the observed results."