Birthday deaths

No.13901545 ViewReplyOriginalReport
https://en.wikipedia.org/wiki/Birthday_effect
>After correcting for confounding factors such as seasonality in deaths, elective surgery, and people born on February 29, there was a significant increase in deaths in the week before the individual's birthday for men, and in the week after the birthday for women – in both cases, mortality did not peak on the birthday, but close to it. This effect was consistent across age and race cohorts.
Scientifically, why is this?