A systematic review of the scientific literature has found preliminary evidence that hearing aids could help keep the human brain young and fit as a person ages.

When researchers in Singapore reviewed eight long-term studies on adults who are hard of hearing, they found participants who wore hearing aids were 19 percent less likely to show signs of cognitive decline compared to those who did not.

A follow-up meta-analysis of 11 papers on hearing loss revealed that after using hearing aids, participants scored 3 percent better on short-term cognitive tests.

The findings suggest there might be impressive brain benefits to hearing aids, but the authors note that further investigation will require rigorous randomized trials.

This isn't the first time hearing loss has been associated with cognitive decline. In fact, a loss of hearing is one of the top modifiable risk factors for dementia, along with smoking, physical inactivity, and obesity.

In 2016, Harvard University researchers found that when hearing loss patients used hearing aids, they scored better and faster on memory and attention tests.

The findings led scientists to wonder if hearing aids were somehow helping to slow cognitive decline. But a systematic review in 2021 found mixed results for that hypothesis. Some studies included in the analysis showed no effect of hearing aids on cognitive decline, while others showed some.

The results of the new meta-analysis are clearer, suggesting that sound is likely to be good for the brain.

Why that is remains unclear, but many theories could be tested by future research.

Hearing aids make sounds loud and crisp for those who are hard of hearing, and perhaps that effect is restoring or restrengthening lost neural connections.

Like prescription glasses, these devices must be individually tuned to a person's specific type of hearing loss, and there's a chance this can reshape certain parts of the brain.

A lot of human interactions are based on sound. And speech, language comprehension, and memory are all closely linked in the brain.

Dementia is also strongly associated with damage to brain regions that help control language. Hearing aids might therefore work to keep those areas of our noggins active, exercising them almost like a muscle.

A second theory suggests that people who are hard of hearing use more cognitive power to listen, leaving little energy for them to focus on or remember what they are actually listening to. In this case, hearing aids could reduce someone's overall cognitive burden, allowing them to focus and remember better.

Yet another theory suggests that hearing loss makes social interactions harder, leading to loneliness, which seems to be a risk factor for dementia as well.

Today, dementia is a leading cause of death and disability worldwide, and researchers predict cases to triple by 2050.

Hearing loss is associated with a 9 percent increase in risk. So if hearing aids can somewhat combat cognitive decline, their impact could be immense.

It's definitely worth more research.

The study was published in JAMA Neurology.