Image copyright Getty Images Image caption Could too much passive TV watching affect the memory?

Watching television for more than three-and-a-half hours a day could leave adults with a deteriorating memory, a study suggests.

Tests on 3,500 adults over 50 found that verbal memory decline was twice as bad in couch potatoes, compared to lesser TV watchers, over six years.

Our memory naturally gets worse as part of the ageing process.

But this happened faster the more TV was watched, University College London research found.

The researchers cannot be sure that TV was the cause of more rapid memory decline, but they say it could be that watching it for long periods stopped people from doing other more stimulating activities such as reading, and exercising.

The study, in Scientific Reports, found that those who watched television for more than three-and-a-half hours a day experienced, on average, an 8% to 10% decrease in verbal memory.

For those watching less than that per day, it was around 4% to 5%.

There was no evidence of TV having an impact on language fluency.

Dr Daisy Fancourt, from the UCL Institute of Epidemiology and Health Care, said that while watching television may have educational and relaxation benefits, "overall this suggests that adults over the age of 50 should try and ensure television viewing is balanced with other contrasting activities".

Study participants, from England, were tested on how well they could remember a list of 10 common words and asked to list as many words in a particular category in one minute.

They were asked how much TV they watched each day and monitored from 2008-09 to 2014-15.

Image copyright Getty Images

The research took into account other potential explanations for memory decline including lifestyle factors, and other behaviours, such as time spent sitting, and exercising.

Although the study did not ask people what they were watching on TV, some types of television could have a greater effect on cognitive decline, it said.

"Older people tend to like watching more soap operas, which can be stressful because they identify closely with the characters," says Prof Andrew Steptoe, from UCL.

"This may create cognitive stress which could contribute to memory decline."

Don't panic

Prof Dame Til Wykes, professor of clinical psychology and rehabilitation from King's College London, said being a passive TV observer may be a potential explanation for the study findings.

"There is still a lot we don't know, such as whether memory reductions are affected by what we watch, whether we watch alone or whether you interact with the TV like those on Gogglebox. We also don't know whether changing behaviour would improve memory.

"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."

Dr Bob Patton, lecturer in clinical psychology, University of Surrey, said older adults (and their carers) should be mindful of too much time spent watching TV.

"While TV may not rot the brain as traditional wisdom may suggest, even moderate watching is associated with some very real changes among viewers aged over 50."