In this season when we are meant to be thankful, but when so many of us have had so many reasons to be otherwise- we have received a timely, welcome bit of universally good news. Rates of dementia in the United States appear to be declining.
This news reaches us courtesy of a study published recently in JAMA Internal Medicine. The investigators used standard, validated measures of cognitive function and dementia in two groups of more than 10,000 people in the U.S. with an average age of roughly 75 in the year 2000, and again in 2012. The overall rate of dementia declined over that span from 11.6% to 8.8%.
Taking this news at face value, it is extremely encouraging. There have been rather dire projections that with the population in the U.S. and other developed countries aging, rates of dementia would rise in tandem. Alzheimer’s and related conditions are devastating, obviously, so the human cost of such a rise- imposed on victims of the condition and their caregivers alike- is the principal concern. But these projections also pertain to the financial devastation wrought by a tidal wave of dementia-related healthcare costs crashing into a system already drowning in the costs of chronic disease.
Expecting dementia rates to rise and seeing them fall is simply good news. But inevitably, the whole story is not quite so simple.
For one thing, projections about a rise in dementia rates do relate directly to aging of the population, while this study matched its cohorts for average age. In fact, the mean age of the 2012 cohort was slightly less than the earlier group, although from a statistical perspective that were nearly equivalent. Still, the 2012 cohort certainly was not older- and it is the increase in numbers of ever-older people that was predicted to drive an increase in dementia rates. So, what if we compared a cohort of 10,000 people now with a mean age of 80, to a cohort from a decade ago with a mean age of 75?
The new study does not answer this question. The more recent study cohort did have more people over age 85 than the earlier cohort, even though the average age of the group was trivially lower, not higher. The study methods did include adjustment for age, and the decline in dementia over time remained significant. So, the good news here appears to be fairly robust- but not robust enough to preclude the feared increase in the prevalence of dementia as the mean age of the population ascends.
The basic finding of this study begs the obvious question: why? The only obvious explanation the study itself contributes is education. The more recent study cohort had significantly more educational attainment than their predecessors from a decade ago. Because this is an observational study, and not an intervention designed to establish cause and effect, it can only tell us that more years of education appear to be associated with less risk of dementia in older age.
This association is certainly plausible. Much prior research suggests that the brain, like the body, is subject to the “use it or lose it” adage. Education is brain exercise, and plausibly defends against what we might call “cognitive atrophy.” That much more so if more education in turn leads to more intellectually demanding work. The study suggests that is likely, as average income and socioeconomic status were significantly higher in the more recent study group. Whatever the direct benefits of education, the indirect benefits over time of more opportunity, more security, and more mental stimulation on the job and perhaps off as well, are apt to be greater.
This finding is promising, since education in our population is something we have the capacity to modify. The advantages to raising population-wide, average educational attainment are diverse and compelling, but that much more so if reducing the lifetime risk of dementia is in the mix. But, this finding is concerning as well. A shift in social priorities away from investments in education and the reduction in disparities that prevail in that area could certainly threaten to reverse the favorable trend.
The paper notes other associations of interest, if not of entirely obvious meaning. Rates of diabetes, heart disease, and obesity were higher, not lower, in the more recent cohort; rates of dementia were lower despite these liabilities, as was the rate of impaired daily function. This might be testimony to the power of modern medical treatment. Newer, better drugs and procedures do very little to prevent cardiometabolic risk factors or the diseases associated with them, but do defend robustly against their dire complications, such as heart attack, stroke, premature death, and perhaps- dementia.
Ironically, this paper is almost entirely silent on the topic long known to have the greatest potential to prevent dementia, namely: lifestyle. The word itself does not appear in the paper at all. Exactly one line in the discussion refers to diet and physical activity, in parentheses, when the authors note that: “Higher levels of educational attainment are also associated with health behaviors (e.g., physical activity, diet, and smoking)… which may play a role in decreasing lifetime dementia risk.”
The new study leaves us, as research so often does, with more questions than answers. But we may gratefully imbibe the dose of good news, even as we work to know just where it came from, and how we might go from a cup half full, to one full to the brim.
For now, though, we do know that risk factors for dementia are much the same as those for type 2 diabetes and heart disease, which in turn we know how to prevent with lifestyle. We could do a world of good for bodies and minds alike by persuading hearts and minds around the world to put to full use at long last knowledge we have long had about the primacy of lifestyle.
