In 2017, The FA and the PFA appointed Dr William Stewart and colleagues at the University of Glasgow and the Hampden Sports Clinic to lead an independent research study into the incidence of degenerative neurocognitive disease in ex-professional footballers. This is one of the most comprehensive studies ever commissioned globally into the long-term health of former professional footballers.

Today, October 21st 2019, the results were published. On average, the former professional footballers in this study lived three and a quarter years longer and were less likely to die of many diseases such as heart disease or lung cancer. However, they were more likely to die of dementia. The research found that the health records of 11% of the former footballers who had passed away stated that they had died from dementia, compared to around 3% for the socio-demographically matched sample.
 
The study showed through statistical analysis on the full data set that the professional footballers in this research were around 3.5 times more likely to die of dementia than the matched population. However, overall, this group of former professional footballers did not on average die earlier of dementia than dementia sufferers in the general population. 

You can find more information on the FA website below.