Senator John McCain, when up against George W Bush to be the Republican nominee for the 2000 presidential election, revealed medical records that included details of the trauma resulting from his experiences in the Vietnam war. When it came to demonstrating a similar openness over the extensive surgery he underwent for a malignant melanoma on his face he was much less forthcoming. A press conference for medical journalists held in Arizona in May this year was in fact a video conference with his medical specialists elsewhere, and the distinguished medical journalist of the New York Times, Lawrence Altman, was not even able to ask a question.

Millions of voters, however, never even registered that he had had a melanoma. What concerned them was Senator McCain’s age. At 72 he would have been the oldest person to have been elected president for the first time.

Having just written In Sickness and In Power, a study of illness among prime ministers and presidents over the past century, I have come to three interrelated conclusions: many heads of government do not …