Several recent studies have shown dementia cases have been declining among those born later in the last century, according to an analysis released Wednesday.
In an article published in the New England Journal of Medicine, a group of researchers from the Group Health Research Institute, the University of Michigan, the University of Washington and the University of California, San Francisco, found recent research has shown that rates of dementia have declined particularly for those most at risk of developing dementia and Alzheimer's disease.
"Of course, people are tending to live longer, with worldwide populations aging, so there are many new cases of dementia," said Eric Larson, executive director of the Group Health Research Institute, in a statement. "But some seem to be developing it at later ages - and we're optimistic about this lengthening of the time that people can live without dementia."
Dementia is an umbrella term that encompasses a number of mental illnesses associated with a decline in mental ability, enough to interfere with everyday life, such as memory loss. According to the Alzheimer's Association, Alzheimer's disease accounts for 60 to 80 percent of all dementia cases, with more than 5 million Americans currently living with the disease.
In 2008, Larson and Kenneth Langa, a professor at the University of Michigan, found the decline coincided with higher levels of education and income, as well as improvements in health care and lifestyle, such as working to prevent high levels of cholesterol and blood pressure.
Larson and Langa looked at data from the national Health and Retirement study for adults over the age of 70 from 1993 to 1995 and 2002 to 2004. They found that in 1993, approximately 12 percent of the participants had a cognitive impairment consistent with dementia, compared with 8.7 percent in 2002.
Since then, several European studies have also found similar results.
A study published in July from a British group of researchers, for example, found that the number of older adults with dementia in the United Kingdom had declined significantly in the past 20 years. According to the study, there are 214,000 fewer cases of dementia than predicted - about a 24 percent reduction.
Another study released by Dutch researcher Elisabeth Schrijvers in 2012 observed adults between the ages of 60 and 90. A group of adults who began observation in 2000, as opposed to those observed beginning in 1990, was less healthy but showed a lower frequency of dementia cases.
"This is a fascinating example of personal health changes earlier in life having an impact on personal and public health late in life," said Kristine Yaffe, a professor at the University of California, San Francisco, in a statement. "Still, we need to be aware that recent increases in obesity and diabetes threaten to reverse these gains, because of the impact these conditions can have on the aging brain.
Although obesity and diabetes epidemics are not currently affecting the age groups most at risk for developing dementia, compared with other groups of the American population, Yaffe said, it's only a matter of time.
The researchers said it's important to find ways to better prevent these health risks that can increase a person's chances of developing dementia.
"As luck would have it, preventing obesity and diabetes jibes with preventing dementia," Larson said. "In other words, we must focus on exercise, diet, education, treating hypertension, and quitting smoking."