In the book, "The Fitzgeralds and the Kennedys", written by the historian Doris Kearns Goodwin,  John F Kennedy was diagnosed with Addison's Disease, in a London Clinic after becoming ill while in England in the late 40's.  This was kept quiet and was never questioned until years later, during the height of the 1960 presidential primary campaign, when it was revealed by Lyndon Johnson's workers. I have read other stories that said  John Kennedy suffered by Addison's Disease