Fight Aging!

The risk of suffering dementia has fallen in recent years. The researchers involved in the paper here are reporting on epidemiological data, so the underlying reasons for this decline remain to be established conclusively. If I had to guess, it would be the increasing focus on control of blood pressure and other preventative cardiovascular treatment in medical practice. Dementia is driven in large part by the age-related failures of the vascular system. Stiffening of blood vessels leads to hypertension, which in turn damages sensitive tissues either through nothing more than greater pressure, or through greater rates of structural failure in small blood vessels, killing tissue one tiny volume at a time. There are other, less immediately physical mechanisms by which higher blood pressure degrades the normal operation of the brain as well, such as disruption of immune cell behavior. So it is entirely plausible to think that the approaches that have successfully reduced the risk of cardiovascular disease over the past few decades are also having an impact on dementia. Interestingly, the data in the paper suggests that the more recent improvements are not due to that cause, but you always have to weigh the details of any one paper against the bigger picture that emerges from all recent work on the topic.

Dementia, a decline in memory and other cognitive functions that leads to a loss of independent function, is a common and feared geriatric syndrome that affects an estimated 4 to 5 million older adults in the United States and has a large social and economic impact on patients, families, and government programs. Although the number of older adults with dementia in the United States and around the world is expected to grow up to 3-fold by 2050 owing to the large increase in the size of the elderly population, recent studies suggest that the age-specific risk of dementia may have actually declined in some high-income countries over the past 25 years, perhaps owing to increasing levels of education and better control of key cardiovascular risk factors, such as hypertension, diabetes, and hypercholesterolemia. For instance, the incidence of dementia among older participants in the Framingham Heart Study declined by about 20% per decade between 1977 and 2008, and the decline in risk was seen only among those with at least a high school education. If confirmed in representative populations, a decline in age-specific risk for dementia would have important implications for public health and public policy. For instance, a recent population-based study of dementia in England found a 24% decline in the expected number of cases of dementia between 1991 and 2011 (a 6.5% prevalence among older adults in 2011, compared with 8.3% in 1991), which translates to more than 200,000 fewer cases of dementia.

There have been changes over the past 2 to 3 decades in both the prevalence and treatment of cardiovascular risk factors that also influence the risk for dementia. For instance, 23% of US adults were obese in 1990 compared with 35% in 2012; among adults 65 years or older, the prevalence of diabetes increased from 9% to 21%. However, intensity of treatment for diabetes, hypertension, and high cholesterol level has increased with more patients achieving treatment goals, and a significant decline in the vascular complications of diabetes such as heart attack, stroke, and lower-extremity amputations, suggesting that there could be a "spill-over" benefit of a decline in the vascular-related risk for dementia. Rising levels of education among US adults over the past 25 years may also have contributed to decreased dementia risk. The proportion of adults 65 years or older with a high school diploma increased from 55% in 1990 to 80% in 2010, while the proportion with a college degree increased from 12% to 23%. More years of formal education is associated with a reduced risk of dementia, likely through multiple causal pathways, including a direct effect on brain development and function (i.e., the building of "cognitive reserve"), health behaviors, as well as the general health advantages of having more wealth and opportunities.

In a large nationally representative survey of older Americans we found that, among those 65 years or older, the prevalence of dementia decreased from 11.6% to 8.8% between 2000 and 2012, representing an absolute decrease of 2.8 percentage points, and a relative decrease of about 24%. Educational attainment increased significantly, with those 65 years or older in 2012 having nearly 1 additional year of education compared with the 2000 cohort. After controlling for the socioeconomic factors of education, wealth, and race/ethnicity, controlling for changes in the prevalence of cardiovascular risk factors did not explain much of the additional difference in dementia risk across the two cohorts. Our findings are consistent with those of a number of recent studies that also found declines in dementia incidence or prevalence in high-income countries around the world and also suggest that the trend toward a declining prevalence of cognitive impairment or dementia in the United States that we found between 1993 and 2002 using earlier data has continued through 2012, even with significant increases in the prevalence of cardiovascular risk factors that may increase dementia risk.

Link: http://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2587084