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 recently in Washington, D.C., 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 had significant improvements in mental speed, 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.

“No currently approved medication can rival these effects,” said Laura Baker, an Alzheimer’s researcher who reported the impact of aerobic conditioning on tau protein.

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.”