Study: Dementia incidence may be declining

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Sudra Seshadri, M.D.
Sudra Seshadri, M.D.

Despite concern about a potential increase of cases of dementia in an aging population over the next few decades, a new study suggests that the rate of new cases of dementia actually may be decreasing. 

The study, which was published in the New England Journal of Medicine, uses data from the Framingham Heart Study. Participants in that study have been monitored continuously since 1975 for cognitive decline and dementia, so researchers have been able to diagnose Alzheimer's disease and other dementias using a consistent set of criteria over the past three decades.

“Currently, there are no effective treatments to prevent or cure dementia; however, our study offers hope that some of the dementia cases might be preventable — or at least delayed — through primary [keeping the disease process from starting] or secondary [keeping it from progressing to clinically obvious dementia] prevention,” said corresponding author Sudha Seshadri, M.D., a professor of neurology at the Boston University School of Medicine and Framingham Heart Study senior investigator. “Effective prevention could diminish in some measure the projected explosion in the number of persons affected with the disease in the next few decades,” she added.

Researchers looked at the rate of dementia at any given age and tried to explain the reason for the decreasing risk of dementia over almost 40 years by considering risk factors such as education, smoking, blood pressure and medical conditions including diabetes, hypertension or high cholesterol, among many others. Looking at four distinct periods in the late 1970s, late 1980s, 1990s and 2000s, the researchers found a progressive decline in the incidence of dementia at a given age, with an average reduction of 20% per decade since the 1970s, when data first were collected.

The decline was more pronounced with a subtype of dementia caused by vascular diseases, such as stroke. There also was a decreasing impact of heart diseases, which researchers said suggests the importance of effective stroke treatment and prevention of heart disease. Interestingly, the decline in dementia incidence was observed only in persons with at least a high school education.

The heart study has been shown to be a reliable source of data, although the authors conceded that participants overwhelmingly are of European ancestry and that further studies are needed to extend the findings to other populations. Also, the authors said they did not look at the effects of key variables such as changes in diet and exercise.

The authors warned that the results of their study do not indicate that the total number of people with dementia will decrease anytime soon. Because baby boomers are aging and people are living longer, the burden of dementia will continue to grow.

The number of people aged 65 or more years who have Alzheimer's disease is expected to reach 13.8 million in the United States and 135.5 million worldwide by 2050, barring the development of medical breakthroughs to prevent or cure the disease.

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