The mystery of why the number of over-65s diagnosed with dementia fell 30% in 15 years

Call it the enigma of declining dementia. People are living longer – and the risk of dementia increases with age – but more and more studies are confirming an apparent paradox: the incidence of Alzheimer’s and other similar disorders is plummeting in wealthy countries. A new study has now found that the proportion of older people with dementia has fallen by 30% in just 15 years in the United States. The reasons for this are not clear, but the researchers point mainly to higher educational levels. Previous studies have suggested that illiterate people have three times greater a risk of suffering from dementia.

The researchers analyzed a study group of more than 21,000 people aged 65 or over, which they consider representative of the US population. The results reveal that the proportion of participants suffering from dementia fell from 12.2% in 2000 to 8.5% in 2016, despite the fact that there is no effective treatment available for the disease. The three authors of the paper, led by economist Péter Hudomiet, who in a statement described the findings as “good news,” are affiliated with the RAND Corporation, a leading US think tank.

Furthermore, the phenomenon is repeated in other high-income countries. A decade ago, Dutch epidemiologist Monique Breteler and her team detected a surprising drop in the incidence of dementia in the Netherlands between 1990 and 2005. Scientists associated this finding with a sharp increase in the use of antithrombotic medications, administered in the prevention of cardiovascular diseases, and anti-cholesterol drugs. A couple of years ago, a commission organized by the medical journal The Lancet calculated that altering a dozen risk factors can prevent or delay dementias in 40% of cases. These variables are: lack of education, hypertension, hearing impairments, smoking, obesity, depression, physical inactivity, diabetes, social isolation, excessive alcohol consumption, blows to the head and air pollution.

The new study, published Monday in the scientific journal PNAS, points directly to the effect of education on the analyzed group. The number of women with higher education qualifications rose from 12% in 2000 to 23% in 2016, while among men that percentage increased from 21% to almost 34%. Exercising the brain has been linked with the prevention of dementia.

The proportion of older people with dementia is very similar in Europe and the United States. A consortium of scientists, led by researchers at Harvard University, a couple of years ago estimated that the incidence of dementia in several European countries – France, the United Kingdom, Iceland, Sweden and the Netherlands – fell by 13% decade-on-decade between 1988 and 2015, a similar rate to that observed in the United States. The new study detected an even greater decline: 30% over the course of some 15 years.

Hudomiet underlines two primary factors that appear to explain the drop in the incidence rate of dementias in wealthier nations. “The population is becoming more educated and treatments for cardiovascular risk factors, such as hypertension, have improved,” he says. The study analyzed the possible effects of four of these risk factors: hypertension, diabetes, heart problems and stroke. Hudomiet says that health measures in the prevention of these problems have not improved greatly in the United States since the turn of the century and as such he believes their influence has been “relatively small.”

Alzheimer’s and other dementias, however, remain of great concern. Due to an aging population, and despite a reduction in the percentage of patients, the overall number is increasing.

No effective treatment for Alzheimer’s

German psychiatrist and neuropathologist Alois Alzheimer described the first case of the disease that bears his name in 1906, when he examined a 50-year-old woman with memory problems who suffered episodes of aggression and confusion. More than a century later, the scientific community still does not fully understand the exact causes of dementia. There is also no treatment with proven efficacy, despite the claims made by some companies. The latest potentially promising treatment is lecanemab, which earned US pharmaceutical firm Biogen over $10 billion on the stock market in one day last September when its stock jumped 40%, despite the drug not yet having demonstrated its effectiveness.

The first Alzheimer’s drug to earn FDA approval in the United States, aducanumab, which was also developed by Biogen, has not brought the announced revolution. Approved in 2021, aducanumab is a monoclonal antibody, based on a molecule obtained from a lucid elderly man. The treatment targets amyloid beta proteins, which accumulate between brain cells and appear to be associated with Alzheimer’s. However, the drug’s authorization under the FDA’s accelerated approval pathway proved controversial in the US and the European Medicines Agency has refused to approve aducanumab as it has found no evidence of its efficacy.