Cardiovascular Mortality Increases Over Christmas Holidays

A new study concludes that the “Christmas holiday effect,” reflected in more heart-related deaths during the Christmas holidays (December 25 to January 7), is unrelated to cold weather.

Researchers at the University of Auckland (UA; New Zealand), the University of Melbourne (UNIMELB; Parkville, Australia), and other institutions in the Southern hemisphere conducted a study to separate the effect of seasonality on the “Christmas holiday effect,” reported in a study from the United States, by conducting a matching analysis in New Zealand, where the Christmas holiday period falls within the summer season.

To do so the researchers collected New Zealand mortality data for a 25‐year period (1988–2013), and analyzed it based on the same methodology used in the North American study. The researchers first used locally weighted smoothing to calculate an expected number of deaths for each day of the year; the expected value was compared with the actual number of deaths. Mean age at death was estimated and used to assess the life‐years lost due to excess mortality. In all, there were 738,409 deaths during the 15-year period, including 197,109 reported as cardiac deaths.

The analysis found a 4.2% spike in heart-related deaths occurring over the Christmas period, with the average age of the people who died being slightly lower - 76.2 years compared with 77.1 years at other times of the year. The researchers suggested various possible explanations for the mortality holiday effect, including emotional stress associated with the holidays, changes in diet and alcohol consumption, less staff at medical facilities, and changes in the physical environment, such as visiting relatives. The study was published on December 22, 2016, in JAMA.

“Another explanation could be what the researchers refer to as ‘displacement of death’, during which terminally ill people, for whatever reason, hold off death for a day that is important to them,” said lead author epidemiologist Josh Knight, MSc, of the UA School of Population Health. “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.”

The “Christmas holiday effect” is established in the United States, with spikes in deaths from natural causes at both Christmas and New Year's Day. In the United States, however, the Christmas holiday period coincides with the coldest period of the year, when mortality rates are already seasonally high because of low temperatures and influenza. Previous studies that used statistical techniques to help disentangle the holiday effect from the winter effect found that deaths from natural causes were almost 5% higher than would be expected if the holidays did not affect mortality.

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