Two major new studies have turned the popular perception of dementia on its head. For years, we’ve heard that Alzheimer’s disease and other forms of dementia are on the rise—a prediction that strikes fear in the hearts of both the public and policymakers. But these new reports conclude that dementia rates may be falling, and suggest that some forms of the disease may be preventable.

The studies do not say that dementia will be less of a problem in the future than it is today. Indeed, as 77 million Baby Boomers reach their 80s, millions more people will suffer from these cognitive diseases. But if the reports are correct, the likelihood of developing these illnesses in old age is far lower than many thought.

The two studies were published in the British medical journal Lancet in July. The first was based on two major national investigations of people 65 and older in England and Wales. Between 1989 and 1994, researchers interviewed nearly 8,000 older people and found that 8.3 percent had dementia. Between 2008 and 2011, the researchers interviewed another group of nearly 8,000 people 65 and older. This time, they found than only 6.5 percent had dementia, a stunning 23 percent decline.

In general, the incidence of dementia is very low until people reach age 80, after which it spikes. The British study confirmed that trend, but with sharply lower rates of dementia (especially after after age 80) among those in the more recent group.

For instance, of those aged 85-89, more than one of every four people in the first group had dementia. But the rate fell to one out of every six in the second. Among those 90 and older, nearly four in ten from the first group were struck by dementia, but only three in ten in the more recent survey.

The second study looked at two cohorts of 90-somethings in Denmark. The first was born in 1905, the second in 1915. The results were similar to the British study. At age 95, the 1915 group scored higher in cognitive tests and needed less help with activities of daily living than the 1905 group at age 93, even though their physical abilities were otherwise similar.

These investigations confirm the results of several recent smaller studies and are something of an antidote to the long string of bad news about dementia. For instance, a recent RAND study published in April found that if current dementia rates continue, the overall cost of care will more than double by 2014.

What does this mean? Most important, it suggests that some forms of dementia, especially those related to stoke and other vascular diseases, may be largely preventable. There is no reason to believe that the prevalence of Alzheimer’s disease has declined. But with education, better monitoring of blood pressure, and better diet and exercise, we can reduce the prevalence of certain other dementias, especially for those in their 80s. The Europeans already have.

If this trend is also occurring in the U.S., it may also lessen the projected costs of long-term supports and services here. That, in turn, may ultimately slow the rise in long-term care insurance premiums and ease projected budgetary pressures on Medicaid and other public programs. Today, half of all long-term care insurance claims are for people with dementia.

Questions remain. The studies were, of course, done in Europe, not in the U.S. More work will need to be done to determine if these are trends are occurring in the U.S. as well.

To be honest, I usually ignore dementia studies. Most report supposed new cures or prevention—and they are always overly optimistic and unsupported by the data. Worse, many are cynical, self-serving promotions by those looking to cash in on what is probably an aging public’s greatest fear of old age.

But these Lancet studies are different. They represent serious and important research. They should make us reconsider how we think about the future.