William Shakespeare did it. So did Casablanca actress Ingrid Bergman. The Feminine Mystique author Betty Friedan, too. All were influential figures, and all also died on their birthdays. There’s some statistical evidence to indicate that there’s a better-than-average chance of someone expiring on their date of birth compared to any other day of the year. It’s called the “birthday effect.”

A study published in the Annals of Epidemiology in August 2012 looked at all causes of mortality against the decedent’s date of birth. At first, the data was intended to examine the theory of death postponement, in which an ailing individual might somehow delay the inevitable so they could enjoy another birthday.

Instead, researchers found the opposite. In looking at the mortality data of nearly 2.4 million Swiss people aged 1 year old and up from 1969 to 2008, they discovered there was a 13.8 percent increase in the potential for death on someone’s birthday. For people 60 and over, the increase jumped to 18 percent.

One obvious conclusion is that the deceased may have died by suicide, which is believed to occur more frequently during holidays, birthdays, and other milestones. And while that was part of the equation, the main cause was long-gestating cardiovascular issues such as heart attacks, illnesses like cancer, and even accidents like falls. In fact, men were 44 percent more likely to die via plummeting on their birthday.

“We concluded that birthdays end lethally more frequently than might be expected,” the paper summarized.

So what could be the cause? That’s a trickier question. One theory is that people experience more physical activity on their birthday, either from dancing, sexual congress, or generalized partying. Putting stress on the cardiovascular system could ignite dormant issues and hasten a cardiac-related event.

Another party staple, drinking, could be a reason people tend to have an uptick in falls or other accidents. And there’s a human error component. It’s possible that for a portion of those succumbing to the “birthday effect,” their death dates were mistakenly recorded to match their date of birth. If that happened even a fraction of a percentage of the time, it would be enough to explain the discrepancies.

But what of the original intent of the Swiss study, which was to see if death could be willed into delay? There’s precedent for that. In 1978, a new Australian tax law abolished inheritance taxes for anyone expiring after July 1, 1979 [PDF]. The statistics of death in the country for that last (taxable) week of living and the (tax-free) week following were significant. Roughly 50 deaths that would be considered average for June were tallied in July, as though estate holders clung on long enough to help their heirs avoid tax rate of up to 27.9 percent.

And in 2000, The New York Times observed that the number of deaths in New York City was 50.8 percent higher the first week of 2000 compared to the first week in 1999. One explanation: people on the verge of passing in late 1999 managed to summon their strength and hold on long enough to witness the new millennium.

What conclusions you draw from all this are up to you. While it’s possible your candles could be snuffed out on your birthday due to external circumstances, you may still possess the innate ability to keep them burning through sheer willpower. Just maybe avoid heights and the dance floor.

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