How old is too old to be president?

By Ben Tinker, CNN

Updated 1554 GMT (2354 HKT) October 13, 2015

A<a href="http://www.ncbi.nlm.nih.gov/pubmed/16462555" target="_blank"> study </a>by Duke psychiatrists found John Adams would have been diagnosed with a bipolar disorder.
Photos: U.S. presidents: Ailing in office
John Adams 1797-1801 – A study by Duke psychiatrists found John Adams would have been diagnosed with a bipolar disorder.
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William Henry Harrison battled with dyspepsia and indigestion. Before he had been in office a month, he caught a cold that developed into pneumonia. On April 4, 1841, he became the first president to die while in office.<br />
Photos: U.S. presidents: Ailing in office
William Henry Harrison, March-April 1841 – William Henry Harrison battled with dyspepsia and indigestion. Before he had been in office a month, he caught a cold that developed into pneumonia. On April 4, 1841, he became the first president to die while in office.
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<a href="http://www.cnn.com/2015/06/18/us/gallery/tbt-abraham-lincoln-portraits/">Abraham Lincoln</a> is widely thought to have suffered from depression.
Photos: U.S. presidents: Ailing in office
Abraham Lincoln, 1860-1865 – Abraham Lincoln is widely thought to have suffered from depression.
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The<a href="http://www.ncbi.nlm.nih.gov/pubmed/16462555" target="_blank"> study </a>by Duke psychiatrists found Ulysses S. Grant would have been diagnosed as an alcoholic with social phobias. <br />
Photos: U.S. presidents: Ailing in office
Ulysses S. Grant, 1869-1877 – The study by Duke psychiatrists found Ulysses S. Grant would have been diagnosed as an alcoholic with social phobias.
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<a href="http://www.cnn.com/2007/LIVING/wayoflife/09/28/forgotten.presidents/index.html?eref=yahoo">Chester Arthur </a>was diagnosed with Bright's disease, a fatal kidney condition, after a year in office. He did not seek a second term and died less than two years after leaving office.
Photos: U.S. presidents: Ailing in office
Chester Arthur, 1881-1885 –