Right around Christmas and New Year’s, heart attacks spike, but why? Scientists think they have at least ruled out a cause, and believe it has nothing to do with the weather, despite popular opinion. A study published in the Journal of the American Heart Association bases these findings on data from New Zealand, when the holidays fall int he middle of the summer and yet there is still an uptick of 4 percent in cardiac-related deaths, according to a University of Melbourne statement.

Why? One possibility is the heavy amount of travel during the holidays. People visiting a new area might not be familiar with local medical facilities, or they may forego care. Changes in diet or stress levels may factor in as well, or medical facilities may not be as well staffed.

Researchers have found similar jumps in mortality for certain religious groups after important holidays, which indicates that a postponement of care could play a significant role in the spikes.

“The Christmas holiday period is a common time for travel within New Zealand, with people frequently holidaying away from their main medical facilities,” lead author and researcher at the Centre for Health Policy at the University of Melbourne, Josh Knight, said in a statement.

“This could contribute to delays in both seeking treatment, due to a lack of familiarity with nearby medical facilities, and due to geographic isolation from appropriate medical care in emergency situations.”