There is good news for anyone who's been a little forgetful lately and wonders if it might be a sign of something worse: The rate of dementia and Alzheimer's disease seems to be declining. People are less likely to get them today than they were 30 years ago.

Better control of the risk factors for heart disease, such as high blood pressure and cholesterol, and more schooling are the major reasons for the decline, according to an article in the New England Journal of Medicine. Heart disease is a strong risk factor for Alzheimer's disease. What's good for the heart is also good for the mind.

As it progresses, dementia affects nearly every aspect of mental life. No wonder people fear it. And memory loss is usually the first symptom noticed.

A U.S. study that lasted nearly 20 years found the incidence of dementia in people 65 and older was 5.7% in 1982 and 2.9% in 1998, a drop of nearly 50%. Other studies, from Stockholm and England, also showed this trend, though more modestly.

Dementia is a loss of mental ability severe enough to interfere with normal activities of daily living and lasting more than six months. As it progresses, it affects nearly every aspect of mental life. No wonder people fear it. And memory loss is usually the first symptom noticed.

There were also better numbers for cognitive impairment, a much milder condition than dementia. It also declined among those 70 and older — from 12.2% in 1993 to 8.7% in 2002. Some view cognitive impairment as an early step on the road to dementia, though this is controversial.

Taken together, the studies suggest that the risk of dementia is declining. On-going research should give a more detailed picture of the situation in the years to come. But a tendency to forget your wallet or keys every now and then does not mean that you have dementia. And that seems to be even truer today than it was 30 years ago.

There is a lot you can do to keep yourself sharp. One of the best ways to is to keep mentally active. Anything — from video games, to doing a crossword puzzle, to learning how to play a musical instrument — is probably better than simply fretting over whether you're getting Alzheimer's.

New Insights into the Dementia Epidemic” appears in The New England Journal of Medicine and is freely available.