In a worrying prediction, scientists say the risk of developing dementia anytime after age 55 among Americans is 42% – especially for women, blacks and over 75s – more than double the risk reported by older studies.
And, according to findings of their recent study, that dementia risk translates into an estimated half-million cases this year, rising to 1m new cases a year by 2060.
The increasing number of cases is directly tied to the ageing of the US population. Beyond that, a high risk of dementia is linked to genetic factors, as well as high rates of hypertension and diabetes, obesity, unhealthy diets, lack of exercise, and poor mental health.
The study authors attribute the previous underestimates of dementia risk to unreliable documentation of the illness in health records and on death certificates, minimal surveillance of early-stage cases of dementia, and the under-reporting of cases among racial minority groups, who are disproportionately vulnerable.
This latest, large study is a collaboration funded by the National Institutes of Health to NYU Langone Health and includes authors from Johns Hopkins University and other US institutions. It relies on information gathered from the ongoing Atherosclerosis Risk in Communities Neurocognitive Study (ARIC-NCS), which, since 1987, has closely tracked the vascular health and cognitive function of nearly 16 000 participants as they age.
ARIC-NCS is also, the researchers say, the longest-followed cohort of African-Americans for cognition and heart health.
Published in Nature Medicine, the study concludes that from 1987 until 2020, there were 3 252 study participants who were documented as having developed dementia.
This translates to an overall lifetime risk for dementia among middle-aged Americans of 42%, which is an average of the 35% risk in men and the 48% risk in women. The excess risk in women was largely due to their lower death rates.
The new results also showed a higher risk among black adults and in those who carried a variant of the APOE4 gene (between 45% and 60%), which codes for a protein that carries cholesterol and other lipids in the bloodstream. Having a certain version of APOE4 is thought to be the single biggest genetic risk factor in developing late-onset Alzheimer's disease.
“Our study results forecast a dramatic rise in the burden from dementia in the United States over the coming decades, with one in two Americans expected to experience cognitive difficulties after 55," said study senior investigator and epidemiologist Josef Coresh, MD, PhD, who serves as the founding director of the Optimal Ageing Institute at NYU Langone.
Coresh, the Terry and Mel Karmazin Professor in the Department of Population Health and a professor in the Department of Medicine at NYU Grossman School of Medicine, said the expected rise in dementia cases is partly tied to the facts that a progressive decline in brain function is often observed starting in middle age, that women overall live longer on average than men, and that about 58m Americans are now over 65.
Among the study's other key findings was that the lifetime risk of dementia increases to over 50% among those who reach 75.
However, previous findings from this study and others indicate that policies designed to prevent heart disease, such as blood pressure control and diabetes prevention, should also slow cognitive decline and prevent dementia.
“The pending population boom in dementia cases poses significant challenges for health policymakers, in particular, who must refocus their efforts on strategies to minimise the severity of dementia cases, as well as plans to provide more healthcare services for those with dementia,” said Coresh.
Loss of hearing among older adults has also been tied to increased risk of dementia. However, only a third of Americans with hearing loss use hearing aids. To address this, Coresh recommends greater monitoring and testing, and possibly even government assistance programmes to support healthy hearing among the elderly, including making hearing aids more widely available and affordable
He also argues that far more resources are needed to tackle racial inequities in healthcare, noting that while dementia numbers among white individuals are expected to double over the next four decades, rates among black people are expected to triple.
For the latest analysis, researchers used data from the ARIC-NCS study and then modelled their projections of lifetime risk using information from the US Census Bureau.
Study details
Lifetime risk and projected burden of dementia
Michael Fang, Jiaqi Hu, David Knopman et al.
Published in Nature Medicine on 13 January 2025
Abstract
Understanding the lifetime risk of dementia can inform public health planning and improve patient engagement in prevention. Using data from a community-based, prospective cohort study (n = 15,043; 26.9% black race, 55.1% women and 30.8% with at least one apolipoprotein E4 (APOE ε4) allele), we estimated the lifetime risk of dementia (from age 55 years to 95 years), with mortality treated as a competing event. We applied lifetime risk estimates to US Census projections to evaluate the annual number of incident dementia cases from 2020 to 2060. The lifetime risk of dementia after age 55 was 42% (95% confidence interval: 41–43). Rates were substantially higher in women, black adults and APOE ε4 carriers, with lifetime risks ranging from approximately 45% to 60% in these populations. The number of US adults who will develop dementia each year was projected to increase from approximately 514 000 in 2020 to 1m in 2060. The relative growth in new dementia cases was especially pronounced for black adults. These results highlight the urgent need for policies that enhance healthy ageing, with a focus on health equity.
Nature Medicine article – Lifetime risk and projected burden of dementia (Open access)
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