This popular myth has its roots in a series of flawed papers published in the late 1980s and early 1990s.
Left-handed people, on average, die younger than right-handed people.
A follow-back study on a large sample of death certificates
Medical Archives, Page 21
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Why do left-handed people think they are special? - Quora
Science Archives, Page 13
WHY DO LEFT-HANDED PEOPLE DIE YOUNGER?
Right Handed People Live longer than Left-Handed People ?, by Ankitkumar Pansuriya
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DNA methylation in peripheral tissues and left-handedness
Why is it thought that left-handers live less long? Chris McManus
What makes right-handed people live longer than left-handed people