Citations? It is easy enough to say something on the order of 14% higher risk of dying on one's birthday than on other days. Where is the evidence? Where can I start researching this? Of course, error can bias this--error such as fitting the agenda.
And we are referring to those who are already 60 and up, not children eating a damn cupcake. For those who are 60 and up, birthdays are stressful events that remind them that they are getting older. They are reminded that they don't have that much more time left--and especially when they are 70, 80, or 90. Unlike when you turn 30 or 40, they just don't have the ability to stand that momentary stress. Thus, it is not surprising a few actually die from it. But, most survive. And most of them do quite fine, only to die later of cancer or pneumonia.
As for children, when do they get sick on their birthdays? A few do, but generally children are less likely to be sick on their birthdays, or Christmas, than on other days. Maybe they need this "stress"? Besides, children enjoy the "stress" coming from a disruption in their routine. Whether it be a birthday, having an abusive parent in the hospital or laid up with a real bad cold, Christmas, or any other positive event, these times are actually good for children (and young adults). Older adults (and I mean those who are old enough to have other health issues and are frail) are less able to take the stress. Of course, they are going to be more likely to die on a birthday (theirs or their children's) or Christmas than on other random days. But, they are even more likely to die soon after a spouse dies, if they get in the hospital even if the issue putting them there is not itself life threatening, or suffer major losses in some area.
Besides this, what is the point of a longer life if it is sterile? Is it worth taking a slight risk of dying having fun? I think most people would rather live a few months less and actually enjoy the time than extend their lives that extra few months and live miserable. And most of those witlesses that would have died on their birthday usually end up dying a few months later while getting ready for field circus, at a Grand Boasting Session or REJECT Astaroth Party or soon after, or if they are pious-sneering and fall a few hours short. Nothing gained--you might just as well have the damn birthday party and enjoy it.