Over the past 30 years, the incidence of dementia has declined an average of 13% every decade in people of European ancestry living in the U.S. or Europe.

Using this trend, researchers at Harvard T.H. Chan School of Public Health estimate that 15 million fewer people could develop dementia by 2040 in high-income countries than if the incidence of the disease remained steady.

"As the populations of the U.S. and Europe age and life expectancy increases, the prevalence of dementia and Alzheimer's disease has dramatically increased, due to the larger pool of people in the ages of highest risk," said Lori Chibnik, assistant professor in the Department of Epidemiology at Harvard Chan School.

"However, our analysis shows that the incidence, or rate of new cases, has been declining, translating into fewer new dementia and Alzheimer's disease cases than what we would have expected."

The results of this study were published in Neurology journal, and noted that 47 million people worldwide live with dementia. Due to the rapidly aging population, the number of people living with the disease is expected to triple over the next 30 years, as is the expected socioeconomic burden associated with dementia.

Previous analyses suggested a decline in incidence over the last 40 years, but most studied smaller populations.

In the current study, Chibnik and her co-authors aggregated data from seven studies that included more than 49,000 individuals with up to 27 years of follow-up.

In addition to showing a total decline in incidence, the researchers also saw consistent trends across different populations from North America and Europe.

In both men and women, incidence decreased, although men had a greater reduction (24%) than women (8%).

The reasons for the decreased incidence are not clear, although several medical interventions that influence blood pressure, cholesterol, and inflammation may have contributed.

The researchers note due to the ethnic background of the participants included in the study, the results may only apply to a minority of the world population, and they recommend that future analyses include more diverse populations.

"The steady decline in incidence over three decades suggests that preventive efforts involving lifestyle education and health interventions such as blood pressure control and antithrombotic medication can offset at least part of the growing burden of dementia from global gains in life expectancy," said Chibnik.

"Providing this evidence of a decline is the first step toward elucidating the factors at play behind that decline and eventually effective interventions to promote brain health." We'll be sure to keep you updated on more positive news from Chibnik and the team.

Source: Harvard T.H. Chan School of Public Health; Featured image: Maria Magdalens, CC license

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