Gary Lineker says he will be undergoing extra checks for dementia this summer after being left fearful of the long-lasting effects of heading a football.Lineker, 60, revealed on talkSPORT that he and Match of the Day colleagues Alan Shearer and Ian Wright are all worried about the chances of developing the disease after years of scoring headers.Research has shown that ex-pros are 3.5 times more likely to die of dementia then the general population, which has led to calls for heading to be banned in the game.The brain disorder has already caused the deaths of four England 1966 World Cup heroes - Nobby Stiles, Jack Charlton, Martin Peters and Ray Wilson.Bobby Charlton was also diagnosed with dementia last year, while former Manchester United.