We can’t be sure that dementia rates are falling in the US

Dementia rates in the US have fallen by 2.8 per cent since the year 2000, according to a study published by the journal JAMA Internal Medicine. The number of Americans diagnosed with dementia fell from 11.6 per cent in 2000 to 8.8 per cent in 2012, the study claimed (but see our analysis below).

Dr Kenneth Langa and his team analysed data from 21,000 adults over the age of 65 in a nationally representative cohort.

The factors contributing to the decline remain unclear. However, the authors noted that the average number of years spent in education increased by one year between those examined in the year 2000 and those in 2012. A higher level of education is believed to be associated with a lower risk of dementia.

Other possible explanations for the decline include improvements in treatment for diabetes, hypertension and high cholesterol, conditions that contribute to plaque building up in the brain, which is a symptom of Alzheimer’s.

The study’s authors, from the University of Michigan, described the results as ‘staggering’. They wrote: ‘Continued monitoring of trends in dementia incidence and prevalence will be important for better gauging the full future societal impact of dementia as the number of older adults increases in the decades ahead, as well as clarifying potential protective and risk factors for cognitive decline.’

Instant analysis
The fall in dementia rates found in this study is far less noteworthy than has been reported. The change in actual numbers, as opposed to a percentage, is small. In 2000 the number of over-65s with dementia was 1,287 out of 10,000; in 2012 it was 1,173 out of 10,000.

What’s more, the cognitive function scoring used to judge whether or not participants had dementia offers almost similar numbers between 2000 and 2012 in all three groups — ‘normal’, those with cognitive impairment, and those with dementia.

The authors explained the data in terms of reduced cardiovascular factors and higher education levels. But, significantly, before 2006 only 20 per cent of the interviews were face to face, and the remainder by proxy (ie, the information was given by someone else) or self-reported. This may lead to bias, possibly explaining discrepancies in the data. Self-reporting of cardiovascular disease may be affected here, especially among those with dementia. The thresholds for cardiovascular disease and dementia (how well they are picked up) will also have changed between 2000 and 2012.

As much as I hate to say it, dementia is largely outside our personal control. By all means, keep your brain turning over, make sure you look after your cardiovascular health, exercise often and watch your diet. But sadly this will affect only some types of dementia.
RM
Research score: 1/5