At least playing it does:

A study commissioned by the National Football League reports that Alzheimer’s disease or similar memory-related diseases appear to have been diagnosed in the league’s former players vastly more often than in the national population—including a rate of 19 times the normal rate for men ages 30 through 49. The N.F.L. has long denied the existence of reliable data about cognitive decline among its players. These numbers would become the league’s first public affirmation of any connection...

We need more data about watching football, of course, but the anecdotal evidence isn't good.