Over 50s who spent more than three-and-a-half hours daily in front of the box were found to experience poorer verbal memory, according to a study published in the journal Scientific Reports.
The findings indicate people should try to balance their viewing habits with other activities, the researchers said.
“There has been interest for over a decade in the effect of television viewing behaviours on cognition but much of this literature has concentrated on children,” co-author Dr Daisy Fancourt said.
“Much less attention has been paid to the effects of television viewing at the other end of the lifespan, despite it being hypothesised for over 25 years that watching excessive television could contribute to the development of dementia.” – Dr Daisy Fancourt
The researchers analysed data from 3,662 adults aged 50 and over between 2008-09 and 2014-15.
Those who watched TV for more than three-and-a-half hours per day experienced, on average, an 8% to 10% decrease in verbal memory across this six-year period. Adults who watched less than this amount experienced an average decline in the memory of words and language of around 4% to 5%.
Dr Fancourt said: “Whilst watching television may also have benefits such as educational benefits from watching documentaries and relaxation benefits as a way of reducing stress, overall this suggests that adults over the age of 50 should try to ensure television viewing is balanced with other contrasting activities.”
The authors suggest watching TV is a passive activity that could reduce the amount of time spent on stimulating activities such as reading.
Even interactive screen-based activities such as gaming can have cognitive benefits, such as improving problem solving, they said.
Chris Allen, senior cardiac nurse at the British Heart Foundation, which part-funded the study, said: “While this study looks at a large number of people and accounts for long-term illnesses and exercise levels, it’s important to remember that cognitive decline is not the same as dementia.
“We all like to curl up in front of the TV and watch our favourite shows.
“But if you’re concerned that the amount of television you’re watching could be having a negative impact on your health, we would advise limiting the amount of TV you watch each day and working in some heart healthy hobbies to your routine.”
Commenting on the findings, Professor Dame Til Wykes, from King’s College London, said: “What this scientifically sound study tells us is that being a couch potato is bad for the over-50s because it is associated with poorer verbal memory but not language fluency.
“This association was found after accounting for lots of other potential explanations including how much time you spend on the internet.”
She added: “Although this result will cause us to think carefully about screen time, a lot more research is needed before we panic and closely measure TV time like a step counter.”