Newly published research in the prestigious journal "The Lancet" examines the factors contributing to the development of dementia. The researchers split the contributing factors into modifiable and non-modifiable causes. Of the modifiable causes (which accounted for 35% overall), hearing loss was the greatest contributor as a risk factor for future dementia.
It is not the hearing loss per se which leads to an increased risk of developing dementia, but instead, it is the indirect effects such as social isolation which is thought to advance cognitive decline and hence an increased likelihood of progression to dementia.
The new research was picked up on by the BBC:
www.bbc.com/news/health-40655566
The actual research paper can be found via this DOI (requires subscription):
dx.doi.org/10.1016/S0140-6736(17)31363-6
Note: the article does not focus on hearing loss explicitly - it is but one of many topics covered; the research concerns dementia and underlying factors.