Mr Obama, the Democratic candidate, began the race as a sprightly 45-year-old with a jet black crop, whose boyish looks could have seen him thought ten years younger.

However, as he enters the final few days of his campaign, with hundreds of sleepness nights behind him, patches of salt and pepper that have sprouted all over his head mark out Mr Obama, now 47, as a man firmly in middle age.

Mr Obama has seemed resigned to his more mature look. "The grey is coming quick. By the time I`m sworn in, I`ll look the part," he told supporters in Colorado in July.

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Mr Obama`s Chicago barber, who goes only by the name Zariff and usually cuts the candidate`s hair each week at a cost of about £13, told Politico.com that his client`s amount of grey was "normal for his age."

Asked whether the senator had ever considered colouring his hair, Zariff said: "No, most definitely not. It will be quite some time before we go there."

Despite there being no conclusive proof that greying is caused by stress, studies suggest it plays a part. Research carried out by Tyler Cymet, of Sinai Hospital in Baltimore, found patients under stress for two or three years went grey sooner than expected.

While the grey emerged while his battle with John McCain, the Republican presidential candidate, Mr Obama has attributed the change in his appearance to the effort required of him to overcome a previous foe.

At the Al Smith dinner earlier this month, Mr Obama laid the blame with Hillary Clinton, his opponent for the Democratic candidacy in the party`s dramatic primary race. "She is the primary reason I have all this grey in my hair now," he told guests.

Telegraph