Let's rush towards Christmas (and 70) with more depressing news!

I was only vaguely aware of estimates of dementia according to age, but this Nature article puts some more certainty to it:

Nearly one in ten people over the age of 70 have Alzheimer’s disease dementia, shows a first-of-its-kind study that paired blood-based markers and clinical assessments to study the disease in Norway¹.

That prevalence is in line with previous estimates for some other white populations². But there were also unexpected differences, including higher disease rates than anticipated in individuals older than 85...

The study, published today in Nature, shows that blood-based tools can improve epidemiological estimates of neurodegenerative disease.

But exactly how to use these tests remains controversial, warns Jason Karlawish, a geriatrician and co-director of the Penn Memory Center in Philadelphia, Pennsylvania. Blood-based markers can be helpful for physicians treating people with dementia and for answering research questions, but they aren’t ready to be rolled out widely as health screening tools.

“It is the kind of test that, in the wrong hands, could cause a lot of harm,” says Karlawish, who was not involved in the study.

 Of course, things get worse the older you get:

Around 10% of participants over the age of 70 had dementia and AD pathology, showing both cognitive impairment and high pTau217, they report. Another 10% had mild cognitive impairments and high pTau217. And 10% had high pTau217 but no signs of cognitive impairment, which the authors refer to as preclinical AD.

These findings are broadly in line with expectations, but there were surprises, too.

Some 25% of people aged 85–89 had dementia and AD pathology, up from previous estimates of around 7% for men and 13% for women in this age group in Western Europeans3. And the incidence of preclinical AD in younger individuals was 8% in those aged 70–74, down from a previous estimate of around 22%.

Anders Gustavsson, a member of the team that compiled the earlier estimates, welcomes the latest data. “I’m not surprised that this study gets somewhat different numbers,” says Gustavsson, who is an adviser to the health-economics consultancy Quantify Research in Stockholm.

The discrepancies probably reflect selection bias, says study co-author Anita Lenora Sunde, a physician and dementia researcher at Stavanger University Hospital in Norway. Previous estimates were made by recruiting participants for brain scans, and people with dementia might not have wanted to or been able to participate. 

The article eventually gets cut off at a paywall, just as it notes that the study indicates (as many others seem to) that higher education may have a protective effect.   Good!