(Reuters Health) - Older adults who develop hearing loss may more likely to experience dementia and cognitive decline than their counterparts without hearing problems, a research review suggests.

Researchers examined data from 36 previously published studies with a total of 20,264 participants who underwent both cognitive evaluations and hearing tests. People with age-related hearing loss were up to twice as likely to have cognitive impairment and 2.4 times more apt to have dementia, the study found.

“The results provide further evidence that hearing loss may be a risk factor for increased cognitive decline, cognitive impairment and dementia,” said lead study author David Loughrey, a researcher at the School of Medicine at Trinity College in Dublin.

About one in three adults from age 65 to 74 have hearing loss, and almost half of people older than 75 have trouble hearing, according to the National Institutes of Health.

Age-related hearing loss can lead to a wide variety of health problems, as it touches on many aspects of daily life, making it harder for people to keep up with conversations, maintain a normal social life and follow a doctor’s advice about other chronic medical problems.

While some previous studies have linked age-related hearing loss to dementia, results have been mixed, Loughrey said by email. For the current analysis, researchers only included studies that tested hearing with “pure-tone audiometry,” the gold standard for assessing structural hearing problems.

Previous studies have indicated that age-related hearing loss may be a risk factor for dementia. However, results from individual studies have been inconsistent, with some studies reporting a small or non-significant association. This may have been due to differences in methods such as the type of hearing assessment used.

It’s not clear how age-related hearing loss and cognitive decline are related, and the study wasn’t a controlled experiment designed to answer this question.

“A possibility is that hearing loss causes cognitive decline through the increased mental energy required to perceive speech, leaving fewer resources available for other cognitive processes, such as memory,” Loughrey said. “Additionally, research suggests that factors such as loss of mental stimulation, depression or loneliness may be associated with a higher risk of dementia.”

The study found a small but statistically meaningful association between hearing loss and a variety of cognitive abilities including executive function, memory, processing speed and what’s known as visuospatial ability, or detecting where things are in a room or on a page.

Hearing aids may have some protective effect, the new analysis suggested.

So-called vascular risk factors like smoking or having high blood pressure or diabetes might help explain declines in some cognitive skills, but hearing loss was still associated with cognitive decline and dementia even after accounting for vascular risk factors.

Shifts in behavior that can accompany both hearing loss and cognitive impairment may explain the link found in the study said Dr. Francesco Panza, author of an accompanying editorial and neuroscience researcher at the University of Bari Aldo Moro in Italy.

“Behavioral mechanisms may explain these associations, such as the withdrawal of older adults from situations in which they may have difficulty hearing and communicating, which may contribute to the development of social isolation, loneliness, and consequent cognitive decline,” Panza said by email.

“Furthermore, several factors and diseases associated with frailty are also related to cognitive impairment, including nutritional factors, metabolic disorders, inflammatory markers, hormones, diabetes, congestive heart failure, and stroke,” Panza added.

Regardless of the reasons for this connection, the study findings suggest that older adults should get routine hearing checks.

“If someone is experiencing hearing loss or has any concerns, it is advised that they check with a medical professional or an audiologist,” Loughrey said.

SOURCE: bit.ly/2Avb5nP JAMA Otolaryngology Head and Neck Surgery, online December 7, 2017.