The odds of getting Alzheimer's disease or other forms of dementia are declining for people who are more educated and avoiding heart disease, a study finds. The results suggest that people may have some control over their risk of dementia as they age.

This isn't the first study to find that the incidence of dementia is waning, but it may be the best so far. Researchers looked at 30 years of records from more than 5,000 people in the famed Framingham Heart Study, which has closely tracked the health of volunteers in Framingham, Mass.

They found that the incidence of dementia declined about 20 percent per decade starting in the 1970s — but only in people who had at least a high school education. The decline in people diagnosed with Alzheimer's wasn't statistically significant, but there were fewer people with Alzheimer's, which could have affected that result.

The study, which was published Wednesday in the New England Journal of Medicine, also looked at risk factors for heart disease and stroke, including smoking, obesity and high blood pressure. They found that the people who had better markers for cardiovascular health, such as normal blood pressure, were also less likely to develop dementia.

"That's telling us that perhaps better management of cardiovascular disease could potentially help in the reduction of dementia," says Claudia Satizabal, an author of the study and an instructor in neurology at the Boston University School of Medicine.

To figure out what this all means, we called Dr. Kenneth Langa, a professor at the University of Michigan who also studies trends in dementia. Here are highlights from the conversation edited for length and clarity.

One of the very confusing things about this is that even though an individual may be less likely to get dementia than they were 40 years ago, the number of people with dementia is going up. Why is that?

It's an interesting and sometimes complicated concept. The number of cases in the population could still be going up in the future because of the larger number of adults.

It's very easy to get your wires crossed when you think of "what's my own individual risk" versus the number of people in the population.

It's certain that we'll have significantly more older people in the United States and around the world, so now the big question is — on an individual level, what's going on with the risk? Does a 70-year-old today have the same risk as one 20 years ago?

And you're finding a trend similar to what the researchers reported this week — a declining risk of dementia in the United States.

We've been looking at data from the Health and Retirement Study, large study funded by the National Institute on Aging and the Social Security Administration. We've been collecting data on older folks in the United States since 1992. We're finding a decline in the prevalence of dementia and cognitive decline very much in line with the Framingham Study report.

You also are finding that a person's level of education is a key driver in dementia risk. Is that because education makes your brain stronger, or that educated people are healthier overall?

That's a big question, and one I'll be focusing on for the rest of my career.

I'll give you my usual researcher on-the-fence answer: I think it's a bit of both. I do think there is a direct biological effect of using your brain and having it interact with the world. You may have heard the term cognitive reserve, which means your brain gets wired up differently if it's challenged.

I'm a believer that there is a causal effect of education on how your brain is challenged. But I definitely would agree that that's not the only pathway.

Education sets you off on a different path in your life; it sends you into different occupations. You may live in different neighborhoods, have less stress, have more money. That gives you access to better health care and social networks.

But still, if I do my 12 years or 14 years or 16 years of school, I don't think that 100 percent determines your risk of dementia.

You've also found that our parents' level of education may affect dementia risk.

It's very intriguing; a mother's education may be more important than a father's education. Again there are lots of complicated pathways you can talk about, but one that we and other researchers are trying to follow up on is whether a more educated mom may interact with a child in ways that are more beneficial to the developing brain of a child.

How your brain is nurtured throughout life is a really fascinating part of this story.

The study published this week didn't look explicitly at exercise, but that does affect cardiovascular health. Could it help prevent dementia?

The evidence both from animals in the cage and epidemiological studies shows that physical activity seems quite important for keeping your blood vessels healthy, and probably some specific growth factors that help the neurons in the brain. The general point that was brought out in the Framingham study is that cardiovascular fitness is very important.

You and other researchers have pointed out that the trend toward more obesity and diabetes in the United States could threaten this more hopeful trend toward lower risk of dementia. When might that happen?

The short answer is I think we don't know. Again, there are so many complicated interacting pathways going on here we can't really be sure what will happen.

Even though the number of people with diabetes has really skyrocketed in the past 20 or 30 years, it also seems to be that having diabetes doesn't have as many bad complications as it did 20 or 30 years ago. There's been a decline in things like heart attacks and amputations due to vascular complications. More aggressive treatment of diabetes and high blood pressure and cholesterol is probably one of the factors that's caused this decline in complications.

We're all terrified of getting Alzheimer's. Given that being heart healthy seems to reduce that risk, why aren't we all exercising like crazy?

It's still complicated, I think. Part of it is that it's a benefit that's going to come to you 20 or 25 years later; it's not easy to motivate people even with something as feared as Alzheimer's disease. I'm an internist. I see middle-aged people with diabetes and hypertension and tell them about these findings. But it can be tough to motivate people.

What else can people do to reduce the risk?

These findings are optimistic; it's not a done deal. But there do seem to be things we can do not only from an individual perspective but from a public policy perspective, for instance, making education as available as possible to people in the United States and other countries.

I tell my patients, "You can do everything right and still get Alzheimer's disease and dementia." It's a question of trying to change your risk to make it as low as possible.

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