An analysis in New Zealand found that 4.2 percent more people died from cardiac-related causes outside of the hospital during the Christmas period than would be expected based on seasonal trends.

Previous research showed a similar association in the U.S. However, the researchers noted that New Zealand is in the Southern Hemisphere, meaning temperatures are higher there during the Christmas period, which they defined as Dec. 25 through Jan. 7.

Lead researcher Josh Knight, BSc, of the University of Melbourne in Victoria, Australia, and colleagues published their results online Dec. 22 in the Journal of the American Heart Association.

“This result in the Southern Hemisphere, with seasonality opposite that in previous reports, helps reaffirm that there is no apparent correlation between any observed Christmas holiday effect and the impact of temperature or seasonality,” they wrote.

The researchers obtained mortality data from the New Zealand Ministry of Health between 1988 and 2013 and categorized deaths as cardiac or non-cardiac. They defined non-Christmas periods as all dates that did not fall between Dec. 25 and Jan. 7.

During the 26-year period, there were 738,409 deaths, including 197,109 cardiac deaths. The mean age of cardiac mortality was 76.2 years old during the Christmas period and 77.1 years old during other times of the year.

The mean age of cardiac death was approximately six months less during the Christmas period compared with the two weeks before Christmas.

For the 2012-2013 Christmas season, which was the most recent period, the researchers estimated there were approximately four additional cardiac-related, out of hospital deaths due to the Christmas holiday effect.

Although the study was not powered to assess causality, the researchers offered a few potential explanations for their findings. They noted that people in New Zealand often travel during the Christmas holiday period, which could contribute to delays in seeking treatment. They also mentioned that there were lower than expected deaths before and after Christmas, so people could possibly modify their date of death based on dates of significance.

“The ability of individuals to modify their date of death based on dates of significance has been both confirmed and refuted in other studies, however it remains a possible explanation for this holiday effect,” Knight said in a news release.

The researchers cited a few limitations of the study, including that they could not link daily temperature to mortality events. They also mentioned that the method they used to estimate the event rates could have led to an underestimation of the Christmas holiday effect.

“By virtue of studying data from a Southern Hemisphere location, we have been able to clarify the likely causes contributing to the Christmas holiday effect; however, we are not able to make a definitive statement about the cause of the effect,” the researchers wrote. “There is the possibility of a displacement effect, in which mortality is being concentrated during the holiday period rather than directly causing additional mortality; however, the use of a different method of estimating the expected deaths will be required to fully explore this issue.”