Barack Obama often jokes in his campaign speeches about a genealogical survey last year that found he is a distant cousin of Dick Cheney.

Now there is more bad news for Obama: a study published yesterday found he is related to George Bush as well.

Researchers at the New England Historic Genealogical Society, founded in 1845, said Obama, the son of a white woman from Kansas and a black man from Kenya, can call six US presidents his cousins: both Bushes, Gerald Ford, Lyndon Johnson, Harry Truman and James Madison. The society, a non-profit organisation, found he is also related to Churchill.

It said it investigated the blood lines of the three presidential hopefuls. One of the oddest connections is that Obama is related to Brad Pitt and Hillary Clinton to Pitt's partner, Angelina Jolie.

Clinton, who is of French-Canadian descent on her mother's side, is a distant cousin of Madonna, Céline Dion and Alanis Morissette. Other distant cousins include writer Jack Kerouac and Camilla, Duchess of Cornwall.

Obama and Bush are 10th cousins, once removed, linked by Samuel Hinkley of Cape Cod, who died in 1662. Pitt and Obama are ninth cousins, linked by Edwin Hickman, who died in Virginia in 1769. Clinton and Jolie are ninth cousins, twice removed, both related to Jean Cusson who died in Quebec in 1718.

While family trees such as these throw up interesting links, genetically they are meaningless. While children carry half the genes of their father, cousins as far removed as Obama and Bush would have no more genetic link than someone they bumped into at random in the street.

The Republican candidate, John McCain, had claimed to be related to the Scottish king Robert the Bruce but, as the Guardian disclosed last week, British genealogists debunked that. The New England genealogists found no royal strain either but established yet another Bush connection: McCain is a sixth cousin of the first lady, Laura Bush.