Certainly in England the link between heading a football and injury leading to death has been proven as the case of Jeff Astle, a former West Bromwich Albion soccer player, shows. In a definitive ruling, based on evidence provided by neurosurgeon Dr. Willie Stewart, the original diagnosis of Alzheimer's has been shown to be wrong and the correct diagnosis of Chronic Traumatic Encephalopathy (CTE) is now recorded as the cause of Astle's death. As his Wikipedia entry shows, he played over 360 times for his club and 5 times for his country.
Former England and West Brom striker Jeff Astle has been confirmed as the first ever British footballer to die as a result of heading a football.
And this article, drawing on data provided by the same authority, expands upon the subject of head injuries in sport.