(CNN)A slower walk as you age has always been a warning sign of increasing frailty that could lead to falls and other disabilities, experts say. Emerging research in small groups of elderly subjects has also found that a slower gait from year to year may be an early sign of cognitive decline. That may be due to shrinking in the right hippocampus, which is the part of the brain associated with memory, according to studies.

But not all signs of cognitive decline predict later dementia -- only 10% to 20% of people age 65 or older with mild cognitive impairment or MCI develop dementia over the next year, according to the National Institute on Aging. "In many cases, the symptoms of MCI may stay the same or even improve," the institute states.

Now, a large, new study of nearly 17,000 adults over age 65 finds people who walk about 5% slower or more each year while also exhibiting signs of slower mental processing were most likely to develop dementia. The study was published Tuesday in the journal JAMA Network Open.

"These results highlight the importance of gait in dementia risk assessment," wrote corresponding author Taya Collyer, a research fellow at Peninsula Clinical School at Monash University in Victoria, Australia.

'Dual decliners' at highest risk

The new study followed a group of Americans over 65 and Australians over 70 for seven years. Every other year, people in the study were asked to take cognitive tests that measured overall cognitive decline, memory, processing speed and verbal fluency.

Twice every other year, subjects were also asked to walk 3 meters, or about 10 feet. The two results were then averaged to determine the person's typical gait.

At the end of the study, researchers found the highest risk of dementia was for "dual decliners," or people who not only walked more sluggishly but also showed some signs of cognitive decline, said Dr. Joe Verghese, a professor of geriatrics and neurology at the Albert Einstein College of Medicine in Bronx, New York, who was not involved in the study.

"Furthermore, dual decliners had a higher risk of dementia than those with either gait or cognitive decline alone," Verghese wrote in an accompanying editorial published Tuesday in the JAMA journal.

A dual association between walking speed and memory decline is predictive of later dementia, a 2020 meta-analysis of nearly 9,000 American adults found.

Yet despite those findings, "gait dysfunction has not been considered an early clinical feature in patients with Alzheimer's disease," Verghese wrote.

Exercise may help

There are things we can do as we age to reverse the brain shrinkage that comes along with typical aging. Studies have found that aerobic exercise increases the size of the hippocampus, increasing some aspects of memory.

Buried deep in the brain's temporal lobe, the hippocampus is an oddly shaped organ that is responsible for learning, consolidating memories and spatial navigation, such as the ability to remember directions, locations and orientations.

Aerobic exercise training increased the volume of the right anterior hippocampus by 2%, thus reversing age-related loss in the organ by one to two years in a 2011 randomized clinical trial. In comparison, people who only did stretching exercises had an approximate decline of about 1.43% over the same time period.

Aerobic exercise means with "air," and is a type of workout where heart rate and breathing increase, but not so much that you cannot continue to function. Types of aerobic exercise can include brisk walking, swimming, running, biking, dancing and kickboxing, as well as all the cardio machines at your local gym, such as a treadmill, elliptical trainer, rower or stair climber.

https://www.cnn.com/2022/05/31/health/walk-speed-dementia-wellness/index.html