People with mild cognitive impairment (MCI) should regularly do physical exercise in order to help improve memory and prevent further decline, according to new guidelines from the American Academy of Neurology, which were endorsed by the Alzheimer’s Association. MCI involves cognitive problems more severe than those seen with normal aging, but milder than with dementia, and affects 10 to 20 percent of people over 65.

The guidelines, published in the journal Neurology in January 2018, pointed to six-month studies finding that twice-weekly workouts—aerobic or strength training—may help improve memory in people with MCI. (They also state that health care providers “may recommend” cognitive training for MCI, though the evidence of benefit is much weaker.) There are no effective drugs or dietary supplements to treat MCI.

What about people without cognitive impairment?

While many observational studies have suggested that exercise can help prevent cognitive decline and dementia in such people, a systematic review of clinical trials on the subject (focusing on aerobic or strength training, tai chi, or multicomponent physical activity) concluded that the evidence is insufficientto draw conclusions. Done for the federal Agency for Healthcare Research and Quality, the review was published in the Annals of Internal Medicine in January 2018.

Regarding the positive but not conclusive results of some of the trials, the reviewers said, “We believe that those findings provide a signal that physical activity offers cognitive benefit but that the studies conducted were not long enough or sufficiently powered to show the true long-term effect of a physically active lifestyle…To be effective, regular physical activity may need to begin earlier in life and be sustained as a lifestyle. Short-term interventions begun after decades of high-risk behavior likely areinsufficient to reduce dementia incidence.”

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Still, since physical activity may slow cognitive decline indirectly by reducing other cognitive risk factors (notably cardiovascular disease, diabetes, and obesity), the reviewers concluded that it