WHO: dementia rose from 19th to 5th among causes of death worldwide over 23 years, while the measured risk of developing it in people over 60 fell by 44% over three decades

WHO: dementia rose from 19th to 5th among causes of death worldwide over 23 years, while the measured risk of developing it in people over 60 fell by 44% over three decades

On 2 October, the World Health Organization published new estimates of causes of death for 2000 to 2023: dementia had risen from 19th to 5th place. That finding was immediately cited as a sign of a sharp deterioration in brain health worldwide. The same day, physician and researcher Wenchang Yue examined the finding using evidence from three long-term studies. A disease’s position in the global ranking of causes of death and an individual’s risk of developing it are two different measures that can move in opposite directions.

According to WHO data, deaths from dementia worldwide tripled between 2000 and 2023, moving the disease from nineteenth to fifth among causes of death. In these statistics, all causes of death share a total of 100%. Ischaemic heart disease remains the leading cause of death worldwide, accounting for 9,5 million deaths in 2023, but its age-adjusted mortality rate has been falling for decades. When heart attacks and infections kill fewer people, other causes, including dementia, account for a larger share of deaths.

Dementia risk depends on age more strongly than the risk of almost any other disease. Seven cohort studies in Europe and North America followed almost 50 thousand people and found 4 new cases per thousand people each year among those aged 65 to 69, compared with 65 per thousand among those aged 85 to 89, almost 16 times as many.

Consider someone who would have died of a heart attack at 62 in 1990 but today receives a stent and lives to 86.

“Cardiology allowed him to reach an age at which dementia incidence is high, without making his brain more vulnerable. That success looks like a dementia epidemic in mortality statistics,” Yue writes.

Improved reporting accounts for part of the threefold increase: in the past, a person with dementia who died was often recorded as having died of pneumonia. A team at Rush University followed 2566 people over 65. Following an Alzheimer’s disease diagnosis, the risk of death among those aged 75 to 84 was more than four times as high. Extrapolating to the US population yielded an estimate of around 503 400 deaths from the disease among Americans over 75 in 2010, although death certificates recorded fewer than 84 thousand that year. Yue explicitly acknowledges that the contributions of improved reporting and an actual increase in cases to the threefold rise cannot be separated. Death registration systems themselves changed over those twenty years, and he says that no one, including WHO, can give an exact breakdown.

Studies that measured the risk of developing dementia found a decline. The Framingham study has followed residents of a Massachusetts town since 1975. Among 5205 participants over 60, the five-year risk of dementia fell from 3,6% in the late 1970s to 2,0% in the late 2000s, a decline of 44% over three decades. A pooled analysis of the same seven European and North American cohorts confirmed the trend: incidence fell by 13% per decade. More recent US data also support this trend: the proportion of people aged 72 and older with probable dementia fell from 11,9% in 2011 to 8,2% in 2021, even as obesity and diabetes became more common in the population. A 70-year-old today has a lower risk of developing dementia within five years than a 70-year-old in 1980. More people now reach 70 and live long enough to receive a diagnosis.

The decline in risk has been demonstrated in white, affluent cohorts in Europe and North America, whereas the increase in cases reported by WHO is global. Falling risk in Rotterdam tells us little about Lagos, where education, blood pressure control and air quality have followed different trajectories.