THE QUESTION Might becoming more physically fit, beginning in middle age, help prevent Alzheimer’s or another type of dementia in old age?

THIS STUDY analyzed data on 19,458 people who were generally healthy at midlife (average age, 50) and took an exercise treadmill test to assess their fitness level. From then until they were in their 70s and 80s, 1,659 of them received diagnoses of a form of dementia. People who were the most fit when middle-aged were the least likely to have developed dementia later in life — 36 percent less likely than those with the lowest fitness scores.

WHO MAY BE AFFECTED? Adults. People who exercise regularly have been shown to reap health benefits that include a longer life and an emotional boost as well as some protection against diabetes, certain cancers and heart problems. Not all adults develop dementia in old age, but those who do often have memory issues and trouble thinking in ways that inhibit such day-to-day activities as eating and getting dressed. More serious cases can affect a person’s emotions and personality.

CAVEATS Most people in the study were white, generally healthy and had access to preventive health care; whether the results would be the same for others is unclear. Other lifestyle factors, such as healthful eating, may have affected the outcome.

The study did not determine specific exercise or fitness details that would be most advantageous for preventing dementia.

FIND THIS STUDY Feb. 5 issue of Annals of Internal Medicine.

LEARN MORE ABOUT dementia at www.

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment’s effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.