Just reading about the campaign schedules of Hillary Clinton and Barack Obama over the past few months has made me want to curl up under my duvet with a cup of camomile tea and a sleeping pill - so I hate to think how they must be feeling. I am writing this before the results of the Kentucky and Oregon primaries on Tuesday, so I don't know whether the gruelling journey has come to an end for Clinton. What I do know is that, after more than a year, at least one Democratic candidate is still in this punishing race.

It was by reading an interview with the political consultant Joe Trippi, who managed How ard Dean's 2004 presidential bid, that I got the clearest sense of how exhausted they must be. Trippi described what the candidates have been going through as a "near-death experience", talked about how he slept for only two or three hours a night during Dean's campaign, and how once - falling asleep while standing in line for a sandwich - he hit the ground with such knocked-out, narcoleptic force that he broke a rib. Trippi is now in a position to acknowledge such fatigue; the current candidates, or candidate, cannot. An ability to cope with extreme sleep deprivation is seen as essential to the job that's up for grabs.

In fact, the ability to cope without sleep has been seen as the main mark of a leader for some years now: a signifier of toughness, machismo, strong-mindedness. Winston Churchill was said to sleep five hours a night on average, but he did at least advocate a substantial daily nap on top of that modest allowance. By the 1980s, the mood was more hard-nosed, with Margaret Thatcher claiming that she got by on four hours a night. In this month's Vogue there is a suggestion that Gordon Brown survives on even less. In a profile of Sarah Brown, the writer notes: "Sarah tells friends that the Prime Minister is the perfect father because he's often still working at 4am, and can settle the boys if one of them wakes." Given that apparently he rises at 6.30am, this suggests the Prime Minister could be surviving on as little as two or three hours' sleep a night.

The fetishisation of sleep loss, the association of lack of sleep with abundance of achievement, stretches throughout our culture. It is there in Condoleezza Rice's admission that she gets up at 4.30am each day to exercise; in reports that Madonna gets only four hours of sleep a night; in those "day in the life of" features in which fam ous people boast about their punishing schedules. It sounds as if I'm doubting the veracity of their claims; actually, I'm not. It just seems weird that sleep deprivation, which has such negative repercussions, has become a badge of honour.

We all like to think that we're too savvy to emulate our leaders, but there's no doubt that their behaviour sets a tone. Last year, the International Labour Organisation found that the UK tops the list of wealthy nations that work excessive hours (a situation not helped by our legislators having included an opt-out when they implemented the EU Working Time Directive, with the result that UK employees can still be contracted for more than 48 hours a week). Another study found that two-thirds of the UK population felt they didn't get enough sleep.

The effects of this are legion. One, of course, is an increased tendency to make mistakes. On the campaign trail, both Obama and Clinton have made errors that have been blamed on fatigue - including her claim to have experienced sniper fire in Bosnia and his claim that 10,000 people had died as the result of a tornado in Kansas (the actual death toll was 12). People who fail to get enough sleep after a long day at work are at much higher risk of being involved in a car accident: driving after 18 hours without sleep has been compared to taking to the road after a few drinks. And those who put in regular overtime are 61 per cent more likely to become hurt and ill than their more relaxed contemporaries.

Sleep deprivation has been linked with heart disease, obesity, chron ic infections, hypertension, depression . . . and death. It is patently not a good idea to work excessive hours with no sleep, but we are constantly told that, to be an effective, successful and notable individual, this is what we must do. All the evidence suggests that we will make less intelligent judgements without sleep - just as we would if we went for an extended period without, say, food or air - but the pressure is on to prove that we can function anyway.

Sleep deprivation is not something to be celebrated; rather, it has been used throughout history as a form of torture. Surely, it is time to acknowledge that the best leaders might be those who insist on getting seven or eight hours' sleep a night as often as possible, who advertise that fact, and who - most importantly - make legislation which ensures that workers have the opportunity to do the same. Now, where's that camomile tea? I'm off to bed.