To fend off dementia, run -- or dance, bike, power-walk or step

Scientists testing experimental drugs to prevent or reverse Alzheimer’s disease have for years endured a drumbeat of inconclusive and disappointing trial results. But dementia researchers meeting in Washington, D.C., this week got some unexpectedly good news on the benefits of a therapy that is readily available, inexpensive to deliver and free of unwanted side effects.

It’s aerobic exercise. And in a head-to-head with available medications for Alzheimer’s disease, it appears it would kick butt.

In older adults with mild cognitive impairment -- a condition that frequently precedes an Alzheimer’s diagnosis -- one study found that a program of regular intensive aerobic exercise reduced the quantity of tau protein found in cerebrospinal fluid -- a rough measure of its presence in the brain. Along with amyloid plaques, tau proteins accumulate in the brain to form tangles that gum up thinking and kill off brain cells in those with Alzheimer’s disease.

Compared with a program of stretching offered to a control group, the aerobic conditioning increased blood flow to regions of the brain involved in memory and reasoning, and brought about corresponding improvements in attention, planning and organizing -- skills that collectively contribute to “executive function.”

A second study found that in older adults with cognitive impairment linked to “mini-strokes” and other forms of cerebrovascular disease, a regimen of aerobic exercise improved memory, selective attention and the brain’s ability to function efficiently.

In a third study, people with mild to moderate Alzheimer’s disease who showed up for two-to-three tough aerobic conditioning classes per week for 16 weeks, experienced significant improvements in mental speed and attention, as measured by a standardized test of cognitive function.

Even among subjects who attended less frequently or exercised at lesser intensities, the aerobic conditioning classes drove down rates of anxiety, irritability and depression, difficult neuropsychiatric symptoms that are common in those with Alzheimer’s disease, and distressing to both patients and their caregivers.

“No currently approved medication can rival these effects,” said Laura Baker, an Alzheimer’s researcher at Wake Forest Baptist Medical Center in North Carolina who reported the impact of aerobic conditioning on tau protein on Thursday. Earlier research by Baker and her colleagues has established that a program of moderate- to high-intensity aerobic exercise also drives down the volume of amyloid plaque in the cerebrospinal fluid of older adults with mild cognitive impairment.

The latest findings, Baker added, “strongly suggest a potent lifestyle intervention such aerobic exercise can impact Alzheimer’s-related changes in the brain.”

In all the studies, subjects were asked to participate in three-to-four sessions of aerobic conditioning -- ranging from 45 minutes to an hour -- a week. The aim was to get participants working at between 70% and 80% of their aerobic capacity.

The new findings come against the backdrop of rising hope that earlier detection and combination therapies may succeed in preventing, delaying or even reversing Alzheimer’s disease. At the 2015 meeting of the Alzheimer Assn. this week, scientists have reported on several promising ways to predict a person’s likelihood of developing mild cognitive impairment and Alzheimer’s disease at least five years before behavioral symptoms become evident.

In the near term, such early-warning tests could help identify potential participants in research studies. But many researchers also believe that earlier detection will improve the prospects that medications, including those that help clear abnormal proteins from the brain, will work to stave off memory loss and brain atrophy.

“Alzheimer’s is a very complex condition that has been extremely hard to address with the ‘one-target, one-treatment’ approach that has been successful in other diseases,” said Maria Carrillo, chief science officer of the Alzheimer’s Assn. “Fortunately, we’re beginning to see some very exciting early results ... of a new treatment approach that targets common components of all the Alzheimer’s proteins.”

The results, she added, may not only help patients with Alzheimer’s disease, but those with other neurodegenerative diseases, such as Parkinson’s and Lewy Body dementia.

Follow me on Twitter @LATMelissaHealy and “like” Los Angeles Times Science & Health on Facebook.