The risk of having a heart attack peaks at 10pm on Christmas Eve, scientists have found, suggesting that stress, sadness and over-indulgence during the festive season can be deadly.
Swedish researchers trawled through the details of 283,000 heart attacks reported in the country between 1998 and 2013 to find out what days were the most lethal.
On an average day 50 heart attacks were recorded, but on Christmas Eve the number jumped to 69, a 37 per cent increase, with incidents clustering at about 10pm, after a day of coping with relatives and eating or drinking too much.
Sweden has its main Christmas celebration on Christmas Eve, suggesting that in other countries the danger zone is more likely to be at 10pm on Christmas Day.
The risk of suffering a heart attack also rises by 22 per cent on Boxing Day. Winston Churchill is said to have suffered a heart attack on December 26 in 1941 while opening a window at the White House following a speech to Congress.
However, New Year's Eve had no associated risk, possibly because symptoms of a heart attack were masked by alcohol, the researchers say.
Instead the risk was 20 per cent higher on New Year's Day, which researchers speculate could be brought on by the after-effects of too much alcohol and food, exposure to cold temperatures at night or sleep deprivation.
Dr David Erlinge, from the department of cardiology at Lund University, said: "The main findings in our study were that traditional holidays were associated with the risk of heart attack. The peak is very pronounced exactly on Christmas Eve and the following two days, so, I think it is something specific for the way we celebrate.
"We do not know for sure, but emotional distress with acute experience of anger, anxiety, sadness, grief and stress increases the risk of a heart attack. Excessive food intake, alcohol, and long distance travelling may also increase the risk.
"Interestingly, the pattern of increased risk in the morning which dominates the rest of the year was reversed at Christmas, with an increased risk in the evening, indicating that the stress and eating during the day triggered the heart attacks.
"People should avoid unnecessary stress, take care of elderly relatives with risk of heart problems and avoid excessive eating and drinking."
The risk was also found to be higher on Monday mornings - particularly at 8am - but fell slightly during the Easter holiday and on days of major sporting events such as the Football World Cup.
The rise may also be linked to the flu season, which also raises the risk of heart attacks, particularly for over-65s with cardiovascular problems.
The research was published in the BMJ.