For some, dementia risk is dropping

The risk of getting dementia - for people with at least a high school education - has been declining by 20 percent per decade since the late 1970s, according to a striking new study published Wednesday in the New England Journal of Medicine.

Yet the country still faces a tsunami of new dementia cases. By 2025, just one form of dementia, Alzheimer's disease, will rob 7.1 million people over age 65 of their memories, their ability to function, their very personalities - a 40 percent increase from today. The Alzheimer's Association has predicted that, by 2050, the disease will cost $1.1 trillion.

Both trends appear to be true. The aging of the baby boomers means that dementia cases will surge to an all-time high because of the sheer number of older people who are living longer. But despite the popular perception that getting old often means people go gray and begin to lose their memory, the new data strongly suggest that, over the last few decades, the risk of developing dementia has receded for people with at least a high school education, raising hope that it might be possible to prevent one of the scariest risks of aging.

The population of people studied was "overwhelmingly of European ancestry," making it unclear whether the results apply to other ethnic groups.

"Can we, a couple of decades down the road, bend the arc? . . . Stroke used to be second leading cause of death, and now it's the fifth. Maybe we can do this for dementia, too," said Sudha Seshadri, a professor of neurology at Boston University School of Medicine, who led the study.

What the study can't answer is the obvious next question: Why?

Some of the improvement is linked to better control of blood pressure and cardiovascular health and a decrease in the risk of developing dementia after a stroke. The drop was led by a decrease in dementia caused by blood flow problems; the decline in Alzheimer's disease was not statistically significant, meaning it could be due to chance. Seshadri plans to dig deeper into the data to try and discern what environmental factors or lifestyle changes might explain the changes.

"What I would say is we need to take that message to redouble our efforts, not to become complacent. We are doing something right," Seshadri said. "So if we understand what we are doing right, we can perhaps activate it."

Seshadri and her colleagues examined data from the long-running Framingham Heart Study, which has a storied reputation in medical history. Scientists began collecting data from more than 5,000 residents of Framingham, Mass., in 1948. In the decades since, those data have been a goldmine and researchers have continued to follow the original subjects' offspring.

It is best known for helping scientists make the connection between cardiovascular disease and high cholesterol, blood pressure, and obesity. But in 1975, the panel of tests that the study subjects took was expanded to include a cognitive assessment.

The new study showed that the risk of developing dementia was declining, providing the strongest evidence yet of an unexpected phenomenon that had been sporadically reported in various data sets over the years.