The rate of heart attack increases during the holiday season, but not just because of cold weather or the exertions of snow shoveling.

Researchers examined heart attack rates in New Zealand, where Christmas falls during summer and the temperature hovers in the 70s. The study is in the Journal of the American Heart Association.

There were 197,109 cardiac deaths between 1988 and 2013 in New Zealand, with a disproportionate number, 26,257, occurring between Dec. 25 and Jan. 7. During that holiday period, the number of cardiac deaths outside the hospital went up by 4.2 percent compared with the rest of the year.

Heart-related deaths during the holiday season rise by a similar rate in the United States, where it tends to be much colder in most parts of the country.

The authors suggest that changes in diet, alcohol consumption or emotional stress during the holidays could contribute to the effect.

“This is an observational study, and we can’t be precise about causes,” said the lead author, Josh Knight, a research fellow at Melbourne University, though holiday travel may also play a role. “It appears that delaying treatment is a significant risk that can turn a survivable event into a fatality. So if you’re traveling, know where to get treatment, and don’t delay getting it.”