Dementia

The number of people living with dementia is rising everywhere. The risk at any given age has fallen in high-income cohorts studied over the last three decades. In the United States, England, the Netherlands and Sweden the fall was something like a tenth to a quarter per decade, plausibly from better education, blood pressure control and less smoking. Whether that fall continues, has stopped, or reverses with obesity and diabetes is the open question. The evidence no longer agrees: the newest cohorts show a flattening in some countries and continued decline in others.

Earlier detection makes the count harder to read. Diagnosis rates rose sharply in England after 2010, when doctors were encouraged to record it. Blood tests for the proteins of Alzheimer's disease are now accurate enough to enter clinical use. They will find cases years earlier, and so raise recorded incidence without changing the underlying risk. The cohort studies that measure incidence directly are small and slow.

Treatment has arrived, and its effect is modest. The first antibodies that clear amyloid slow decline by a few months over eighteen months in early disease. The cost, and the risk of side effects, has led some health systems to license them but decline to fund them. Prevention rests on the risk factors. The latest estimates attribute a substantial minority of cases to modifiable exposures, hearing loss and hypertension prominent among them. The first trials of treating those exposures have shown effects on cognition, not yet on dementia.

Dementia is now the leading recorded cause of death in England and Wales, and is rising in most countries' statistics. A large part of that rise is certification. Doctors record it more, coding rules changed, and people die with it more than of it. The prevalence trend is certain. The incidence trend is contested. The two are routinely reported as though they were the same thing.

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