The authors are Eric B. Larson, MD, MPH, executive director of Group Health Research Institute and Group Health's vice president for research; Kristine Yaffe, MD, a professor of psychiatry, neurology, and epidemiology and biostatistics, the Roy and Marie Scola endowed chair in psychiatry, and vice chair for clinical and translational research in psychiatry at the University of California, San Francisco and the San Francisco Veterans Affairs (VA) Medical Center; and Kenneth M. Langa, MD, PhD, a professor of medicine at the University of Michigan and VA Healthcare System. Dr. Larson is also an adjunct professor at the University of Washington Schools of Medicine and Public Health.

"Of course, people are tending to live longer, with worldwide populations aging, so there are many new cases of dementia," Dr. Larson said. "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 in those affected may be starting later in the course of life, closer to the time of death.

In 2008, Drs. Langa and Larson reported one of the first studies suggesting a decline in U.S. dementia rates, using information from the U.S. Health and Retirement Study. They found that the decline tracked with education, income, and improvements in health care and lifestyle. Since then, several studies in Europe have confirmed this trend—and the reasons behind it.

"We're very encouraged to see a growing number of studies from around the world that suggest that the risk of dementia may be falling due to rising levels of education and better prevention and treatment of key cardiovascular risk factors such as high blood pressure and cholesterol," Dr. Langa said. He added that it will be very important to continue to follow these trends in the population given the wide-ranging impact of dementia on patients, families, and the health care system.

"This is a fascinating example of personal health changes earlier in life having an impact on personal and public health in late life," Dr. Yaffe said. She and Dr. Larson have reported that regular exercise may help delay dementia. In an earlier publication this year in the New England Journal, Dr. Larson's team reported that people with lower blood sugar levels tend to have less risk of dementia. And Dr. Yaffe and her team have focused on a host of other lifestyle factors that have the potential to reduce risk.

"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," Dr. Yaffe said. "The obesity and diabetes epidemics are not affecting age groups most at risk for dementia—yet." But it's just a matter of time.

"To help more people avoid dementia, we'll need to find better ways of preventing obesity—and avoiding obesity-linked health risks, including diabetes and dementia," Dr. Larson said. Narrowing health disparities will also be crucial, because obesity and diabetes are more common among certain racial and ethnic minorities and others who lack access to education and health care.

"As luck would have it, preventing obesity and diabetes jibes with preventing dementia," Dr. Larson said. "In other words, we must focus on exercise, diet, education, treating hypertension, and quitting smoking."

On December 11, the New England Journal of Medicine will post a podcast of Dr. Larson discussing this perspective piece, and that day he and Dr. Yaffe will also address the U.K. Department of Health's G8 Dementia Summit in London. The Summit aims to develop coordinated global action on dementia.

Literature on the subject:
Dementia Care Research
Scientific Evidence, Current Issues and Future Perspectives
Jochen René Thyrian & Wolfgang Hoffmann (Eds.)