By examining the changes between each successive cohort, he calculates that dementia rates have been declining by 2.5-3% for each calendar-year cohort.
Making memories Big questions remain about why dementia rates are falling and whether they will continue to drop.
Yet even relatively small annual changes in the rate of dementia, when compounded over 30 years, can lead to much happier outcomes.
That is not easy, in large part because dementia is a condition with multiple causes that typically develops slowly over decades before clearly manifesting itself.
“It really changed the way we think about dementia,” says Miia Kivipelto of the Karolinska Institute in Stockholm, who led some of these studies.
WHEN ERIC STALLARD, an actuary and academic, began looking into the incidence of dementia among elderly Americans, he was so stunned by his findings that he held off publishing his first paper on the subject for two and a half years while he double-checked his work. “I wanted to be absolutely certain,” he recalls, since the numbers defied all expectation. Instead of confirming the received wisdom that America faced an intensifying plague of the condition, they showed that the proportion of old people succumbing to it was in fact shrinking fast. “I was shocked by the declines,” he says. Instead of confirming the received wisdom that America faced an intensifying plague of the condition, they showed that the proportion of old people succumbing to it was in fact shrinking fast. (Unsplash) Mr Stallard has been working for a decade to corroborate this revelation. His findings have, if anything, become even more striking. Last year he and some colleagues published research in the Journal of the American Medical Association showing that, whereas 40 years ago three in every ten Americans aged 85-89 had dementia, by 2024 just one in ten had it (see chart 1). What is more, America is not the only beneficiary of this trend. Between 1988 and 2015 the share of older people being diagnosed with dementia fell by 13% a decade across six countries in North America and Europe, according to a study of almost 50,000 people by Frank Wolters of the Erasmus Medical Centre in Rotterdam, and colleagues. Some smaller studies have also found big declines. Data from the Framingham Heart Study, which has tracked three generations in an American town, show an average drop in new dementia cases of 20% per decade over almost 40 years between the late 1970s and early 2010s. Those who were entering their dotage when Daft Punk’s “Get Lucky” was topping the charts (2013) were 44% less likely to have dementia than those who were doing so when Sting was urging Roxanne to switch off her red light (1978).
Chart 1
Whereas most earlier studies had simply pooled elderly people and then applied a statistical adjustment for age, Mr Stallard looked at narrow bands of ages to compare different cohorts of people over 50 years. By examining the changes between each successive cohort, he calculates that dementia rates have been declining by 2.5-3% for each calendar-year cohort. “In my view it was the Copernican revolution in the field,” he says, turning assumptions about dementia’s spread upside down. Similar cohort studies in various European countries and Japan have found comparable trends there, too. Making memories Big questions remain about why dementia rates are falling and whether they will continue to drop. The growing number of old people in most countries and increasing longevity mean that overall case numbers are still rising, even if a smaller share of the elderly are afflicted. And the good news is largely confined to rich countries, at least for now. But the fear that an epidemic of dementia will soon be running out of control, blighting ever more lives and placing an impossible burden on health systems, is mercifully overblown. The single biggest risk factor for dementia is age. Prevalence doubles roughly every five years after 70. In America in 2016, for instance, just 4% of people aged 70-74 had dementia, but the rate jumped to 9% for those who were 75-79 and again to 18% for 80- to 84-year olds. More than a quarter of those over 85 had the condition. This near-exponential pattern, combined with the rising life expectancy, has long fuelled alarming predictions. In a study published last year in the journal Nature Medicine Josef Coresh, Michael Fang and their co-authors projected that the number of new cases in America would double from around 500,000 a year in 2020 to 1m a year by 2060. A study published in 2022 calculated that the global population of people with dementia will almost triple from around 57m people in 2019 to 153m people in 2050. Mind-bending Such numbers, in turn, feed frightening estimates of the likely future cost of dementia. The direct cost of care (including informally in the home) probably came to around $1.3trn worldwide in 2019 (or roughly 0.8% of global GDP). The burden becomes even greater if one accounts for indirect costs such as patients’ diminished quality of life. These added up to around $781bn last year in America alone (or about 2.5% of GDP), according to a model funded by America’s National Institutes of Health. A paper by Arindam Nandi of the Population Council, David Bloom at Harvard University and others uses an even broader measure that tries to put a price on patients’ suffering (by estimating a willingness to pay to prevent it). It put the global cost of dementia at $2.8trn in 2019 increasing to $4.7trn by 2030, $8.5trn in 2040 and $16.9trn by 2050. Yet such terrifying projections are almost certainly wrong, at least with respect to rich, Western countries. Almost all are based on models in which there is little, if any, reduction in the age-adjusted rate of dementia over the coming decades. Since there will be growing numbers of old people in most Western countries in the coming years, and since those old people will live longer, such assumptions lead to gigantic increases in the projected number of dementia cases. Yet even relatively small annual changes in the rate of dementia, when compounded over 30 years, can lead to much happier outcomes. To show this Chiara Celine Brück and her co-authors at the Erasmus Medical Centre built a detailed computer simulation of 10m Dutch people and then looked at how dementia would progress under two different scenarios. In the first they assumed there would be no change in the underlying risk of dementia over time (other than from ageing) and found, as other mainstream projections have, that the number of Dutch people with dementia would more than double by 2050. In another, they used the research of their co-author, Mr Wolters, who found that the incidence of dementia had been falling by 13% a decade after adjusting for age, and simulated what would happen if the trend continued. They found that, although the number of dementia cases would still increase because of the growing ranks of elderly people, instead of more than doubling by 2050, it would grow by just 43% from the level of 2020. To be more confident about such projections, researchers must determine why so many more people have been keeping their wits and so be able to make a more reasoned judgment about whether the trend will continue. That is not easy, in large part because dementia is a condition with multiple causes that typically develops slowly over decades before clearly manifesting itself. Scientists have long known that dementia has a genetic component. Roughly 25% of the population carries a single copy of a gene known as ApoE4, which is associated with a risk of getting Alzheimer’s (much the most common of the dozens of diseases that can cause dementia) that is 2-3 times greater than the norm. For the 2-3% of the population with two copies of this gene, the risk is 10-15 times greater. Yet many people without these genes get dementia and many who have them do not. The search for other causes of the condition was given a boost in the 1970s in North Karelia, a remote and hard-living region of Finland which had one of the world’s highest rates of heart attacks. To reduce this scourge, health authorities discouraged smoking, monitored blood pressure and encouraged healthy eating. The public-health campaign eventually cut deaths from heart attacks by 84%. An unexpected benefit, says Tiia Ngandu, a researcher at the Finnish Institute for Health and Welfare, was the opportunity for researchers to examine some 40 years of detailed health records for a large population. Memory laws The result was a groundbreaking series of observational studies showing that high blood pressure, high cholesterol, obesity and poor fitness in mid-life all increased the risks of dementia 20 years later. “It really changed the way we think about dementia,” says Miia Kivipelto of the Karolinska Institute in Stockholm, who led some of these studies. “We saw that it was not only a late-life disease that can’t be prevented, but more of a process that starts in mid-life with the possibilities to at least slow the progression.”
Chart 2
