Rates of dementia in each age group show signs of falling.
Figures from the World Health Organization (WHO) suggest that, globally, 47.5 million people have dementia. The figure is expected to rise to 75.6 million by 2030 and to almost triple to 135.5 million by 2050.
Currently, some 5.1 million Americans are living with Alzheimer's disease and other dementias, and the rate is projected to grow as more people live to the age of 65 years and over.
Experts predict that 7.1 million American seniors will have Alzheimer's by 2025, 40% more than in 2015.
By 2050, the number could triple to 13.8 million unless medical breakthroughs succeed in preventing or curing the disease.
The Framingham Heart Study (FHS) was set up in 1948 to investigate the causes of heart disease and stroke. It is now a joint project of the National Heart, Lung, and Blood Institute (NHLBI) and Boston University, MA.
In 1975, FHS researchers began monitoring participants for cognitive decline and dementia, using information from FHS examinations, external clinical records, family interviews and results of examinations by neurologists and neuropsychologists.
Researchers looked at the rate of dementia at specific ages in four time periods: the late 1970s, late 1980s, 1990s and 2000s.
Fall in cases of cardiovascular-related dementia
The findings reveal a gradual drop in the incidence of dementia at any given age, especially in cases of dementia linked to cardiovascular disease (CVD), such as stroke. Rates fell by 20% each decade, particularly benefitting people with high school education and above.
In the late 1970s and early 1980s, the rate was 3.6 per 100 persons, falling to 2.8 per 100 persons during late 1980s to early 1990s, 2.2 per 100 during the late 1990s to early 2000s and 2.0 per 100 from the late 2000s to early 2010s. This represents a drop of 22%, 38% and 44%, compared with the first period.
The results indicate a role for stroke treatment and heart disease prevention in controlling the prevalence of dementia.
Corresponding author Dr. Sudha Seshadri, professor of neurology at Boston University School of Medicine (BUSM) and FHS senior investigator, says that while there is currently no effective way to treat, prevent or cure dementia, it might be possible to reduce the impact in some cases.
This could be through primary interventions to avert the onset of the disease or secondary interventions to slow its development.
Dr. Seshadri comments on the implications of the research in the following video:
Carole Dufouil, research director of INSERM in Bordeaux, France, comments that primary and secondary prevention and enhanced management of CVD and stroke, and their risk factors, might offer new opportunities to reduce the burden of dementia in future.
Cautious optimism: the burden is still growing
The authors warn that the total number of patients with dementia will still continue to grow, as the "baby boomers" are aging and people are living longer.
In the video, Dr. Seshadri cautions that we will still see a rising burden of dementia over the next 2-3 decades, highlighting the importance of understanding what is being done correctly and incorrectly in order to tackle the burden.
Limitations to the study include the fact that most participants are of European ancestry, suggesting a need for further studies into other populations.
The team hopes that the findings will encourage donor agencies and scientists to continue exploring the factors underlying this positive trend.
Medical News Today recently reported that people who have suffered a traumatic brain injury may have similar amyloid plaques in their brain to those found in patients with Alzheimer's.