A new study of over 21,000 Americans age 65 and older has shown that the prevalence of dementia declined significantly between 2000 and 2012. This sounds like good news—and it is—but you need to dig a bit deeper into the study to see what’s really going on.
All the participants in this research are enrolled in a huge study of older adults in the United States called the Health and Retirement Study (HRS). Beginning in 1992, researchers at the University of Michigan have done a biennial survey of a nationally representative group drawing from all regions of the country. As the years have gone by, new groups have been added to the study. You can imagine how much information has been collected since 1992 and the kind of computing power needed to analyze it!
People enrolled in the HRS participate in a telephone interview until they die, quit the study, or are unable to continue (although in the latter case, a care partner may be asked to provide information about the individual). For the study of dementia prevalence, researchers compared the responses of people in the 2000 survey to the responses from 2012. They used the Telephone Interview for Cognitive Status, which categorizes people as normal, having cognitive impairment but no dementia, and having dementia. Obviously this is not the same as having a specific diagnosis of Alzheimer’s or some other form of dementia but it provides a general view of the cognitive status of older people in the US.
In 2000, 11.6% of the participants were classified as having dementia, but in 2012, that number had decreased to 8.8%. This might not seem like a huge drop, but it is statistically significant and certainly better news than if the percentage had risen in those twelve years.
What accounts for the change? The authors examined all their data and concluded that having more years of education and higher net worth were the two key factors. This is important given the fact that between 2000 and 2012 there was also a significant increase in cardiovascular risk factors like hypertension, diabetes, and obesity. However, surprisingly, the researchers found that being obese or overweight in later life (the average age in this study was 75) is actually associated with a decreased risk of dementia! Obesity in midlife increases dementia risk.
Obviously, there’s a lot more to learn about dementia prevalence. Given the fact that the number of people over 65 will double by 2050, there are still going to be a lot of people with dementia even if the percentage of the population with dementia continues to decrease. Also, the finding that more education and greater net worth protect against dementia has implications for the high number of aging Americans with lower educational attainment and more financial insecurity.
Langa, K. M., Larson, E. B., Crimmins, E. M., Faul, J. D., Levine, D. A., Kabeto, M. U., & Weir, D. R. (2016). A comparison of the prevalence of dementia in the United States in 2000 and 2012. JAMA Internal Medicine. Published online November 21, 2016. doi:10.1001/jamainternmed.2016.6807.