It's a subject that science is almost unanimous on. To function at their best, live long and prosper, humans need a good amount of sleep every night. Seven hours, ideally.

So it's a matter of curiosity that many of the world's leaders – the men and women charged with helping us all to live long and prosper – have spoken of their extreme sleeping habits. Few, it seems, respect that hallowed seven hour mark.

During a wide-ranging interview with Fox News's Bill O'Reilly this week, Donald Trump revealed that he is sleeping four to five hours a night in his new life as the US top dog. "I'm working long hours, long hours, right up til 12 o'clock, 1 in the morning." What time does he get up? "Five. I eat, I read the papers, I see what's going on on TV."