People who experience hearing loss could be at greater risk of memory and thinking problems later in life than those without auditory issues, research suggests.

The study focused on people who were at risk of Alzheimer’s disease, revealing that those who were diagnosed with hearing loss had a higher risk of “mild cognitive impairment” four years later.

“It’s really not mild,” said Clive Ballard, professor of age-related disease at the University of Exeter. “They are in the lowest 5 percent of cognitive performance and about 50 percent of those individuals will go on to develop dementia.”

Presented at the Alzheimer’s Association International Conference in London, researchers from the US looked at the memory and thinking skills of 783 cognitively healthy participants in late middle age, more than two-thirds of whom had at least one parent who had been diagnosed with Alzheimer’s disease.

The team carried out a range of cognitive tests on the participants over a four-year period, aimed at probing memory and mental processing, revealing that those who had hearing loss at the start of the study were more than twice as likely to be found to have mild cognitive impairment four years later than those with no auditory problems, once a variety of other risk factors were taken into account.

Taylor Fields, a PhD student at the University of Wisconsin who led the research, said that the findings suggest hearing loss could be an early warning sign that an individual might be at greater risk of future cognitive impairment – but added more research was necessary to unpick the link.

“There is something here and it should be looked into,” she said.

It is not the first study to suggest a link between hearing loss and cognitive troubles – previous research has found that the more severe hearing loss is, the greater the risk of dementia.

But it is not yet clear whether hearing loss is the result of changes linked to dementia, or whether hearing loss itself could contribute to cognitive decline. As a result, it is unclear whether treating hearing loss could mitigate against increased risk.

“Potentially it is something you can do something about, which I think makes it really important to understand better,” said Ballard.

In a separate study, researchers from Wisconsin found a link between thinking and memory difficulties, and changes to the fluency of speech. In 219 late-middle aged participants were assessed at the beginning and end of a two year period. The team found that those with early signs of mild cognitive impairment at the start of the study showed a steeper decline in fluency over the two years than those without.

A further series of studies presented at the conference focused on the link between diet and prowess at memory and thinking tasks. While all differed in the range of participants and the type of diet applied, overall the results suggest that eating healthily was linked to a lower risk of cognitive difficulties, and even a lower risk of dementia.

In one study, carried out by researchers in the US with almost 6,000 participants, scientists found that after taking into account a host of factors including smoking, physical activity, health and socioeconomic status, those who stuck best to a Mediterranean or similar diet over the course of a year were about 35 percent less likely to have low scores on cognitive tests than those who did not stick to the regime.

While the study does not show that eating badly triggers cognitive problems, and further work is needed to monitor the impact of the diet over time, Claire McEvoy – co-author of the research from the University of California San Francisco – noted that benefits of healthy eating seem to exist on a sliding scale.

“Even moderate adherence to these high-quality dietary patterns showed a protective association with cognitive function,” she said.