A recent editorial in JAMA Neurology (Venturi) suggested that there may be a general decline in dementia risk in the future because of better brain health due to worldwide improvements in the standard of living, in education, and in the prevention and treatment of serious diseases. This provocative speculation contradicts the more common and dire predictions of a significant increase in dementia as the world’s population ages. In this article we explore the latest ideas about normal aging and cognitive decline with an eye towards the future.
Most older people remember lots of ordinary things, like how to sing a familiar song and how to tie a shoe, and many people currently live into their 90s and beyond without any significant signs of cognitive impairment. It may take them longer to recall a word or a name, but their general language ability, vocabulary, and reasoning capacity remains relatively intact.
What does tend to decline in normal aging is mental flexibility. Reliable recollection of facts, events, and practical knowledge becomes more difficult, and it may become challenging to make use of newly learned information. Multitasking and executive functioning that requires speed, verbal, and mathematical reasoning typically slows down, especially after age 70.
Charan Ranganath, in his book “Why We Remember”, suggests that we think of memory like a desk cluttered with crumpled-up scraps of paper. If you think about urgently rooting around on that messy desk, trying to find something important that you’ve scribbled on one of those crumpled scraps, you may begin to feel what it’s like to lose access to your memory.
Mild Cognitive Impairment (MCI) occurs when there is more difficulty with memory and thinking than what is normally expected at a person’s age. Although a person with MCI can still be independent, they may struggle with ordinary tasks and may feel easily frustrated, disorganized, and overwhelmed.
In a 2024 study (Palmqvist) of people whose average age was 70, about 30 percent of people who had been diagnosed with MCI later developed dementia. Dementia involves a further decline in memory and thinking skills, most commonly due to damage to the brain from a variety of causes. A definitive diagnosis of dementia is complicated because its clinical manifestations are very varied. A specific disease-modifying drug for all-cause dementia is not currently available, but some symptoms and underlying causes can be treated.
Mild dementia is characterized by increased confusion, and reading and writing can
become difficult or impossible. If it progresses, repetitive or inappropriate questions and inaccurate answers can make conversation challenging, and it is not unusual for people with dementia to wander and get lost. There is likely to be impulsive behavior and a diminished capacity for empathy and, eventually, difficulty recognizing family and friends. At its most severe, a person with dementia may become completely dependent on others to manage their basic activities of daily living.
Alzheimer’s disease (AD) is the most common cause of dementia. Until the last twenty years, the diagnosis of AD could only be confirmed with an autopsy, at which time the presence of clumps of specific “toxic” proteins in the brain (beta amyloid plaques and neurofibrillary tangles of tau) could be confirmed. Neuroimaging scans can now provide live images of the brain, and a lumbar puncture can measure toxic protein levels in a person’s cerebrospinal fluid. In 2020, a simple blood test to accurately diagnose AD became available. (Palmqvist)
These new ways to observe changes in the brains of live patients have provided a wealth of information that has raised new questions, and even the exact, biologically-based definition of Alzheimer’s disease is up for debate. What if tests indicate significant amounts of toxic proteins in a person’s brain but there are no clinical signs of dementia? Does that person have Alzheimer’s disease? (Peterson) There is evidence that amyloid deposits accumulate in some brains for as long as ten to fifteen years before people exhibit symptoms of cognitive impairment, and it is unclear if the plaque is causing the brain damage or is simply a response to it. (Jia) There are many new directions for research now that scientists have the tools that they need.
There are two drugs recently approved by Medicare (lecanemab and donanemab) that dissolve some of the beta amyloid plaque. Unfortunately, they have fairly modest benefits and will not improve a person’s memory. Lecanemab, for example, is said to delay the progression of AD by about five months. These drugs require an extensive commitment of time and money, and they have a high risk of serious side effects. Drug regulators in several countries have declined to approve the drugs out of concern that the risks outweigh the modest benefits, and several major US healthcare institutions have opted not to give the drug to anyone with a problematic genetic
profile (Bogdanich & Kessler).
As part of the search to identify cognitive impairment at the earliest possible point so that effective treatments can be developed to prevent and delay the development of dementia, the concept of Subjective Cognitive Decline (SCD) has recently appeared in the cognitive continuum (Kang). It is derived from the requirement by Medicare that the physician ask a patient who is over 65, at their annual wellness visit, whether they are having any issues with their memory.
Participants 60 years of age and older with normal cognition who participated in the large Framingham Heart Study were asked slightly different variations of that single question, “Do you feel your memory is becoming worse?” Study participants were followed for up to 12 years, and if they had answered “Yes”, indicating SCD, it was found that, over time, they had an increased risk of developing cognitive decline and all-cause dementia. On average, SCD preceded the development of MCI by 4.4 years, of AD by 6.8 years, and of all-cause dementia by 6.9 years. If SCD is established as an early or presymptomatic manifestation of impending neurodegeneration, that diagnosis could lead to new treatments and the prevention of further decline.
While research on cognitive decline continues to focus on diagnosis, treatments, and cures, considerable emphasis has shifted toward studying lifestyle and environmental modifications that can be shown to reduce the risk of decline and delay its progression. Investing in preventative health, like being fitted for hearing aids, has been shown to reduce the amount of brain damage that occurs due to normal biological aging. A 2022 article (Marinelli) estimates that “…nearly 50 percent of all dementia cases are preventable…” Experts agree that, along with physical exercise or staying socially active, engaging in cognitively stimulating activities or hobbies can help protect against cognitive decline by building up mental muscle or “cognitive
reserve” (Dhana).
Some of the healthy lifestyle and environmental modifications that have been statistically validated to reduce the risk of cognitive decline are listed below, and they are discussed in detail here (Butler).
• Eat healthily.
• Find a way to exercise regularly to whatever degree is possible for you. Even modest
increases in physical activity have been consistently shown to be beneficial.
• If you aren’t working or socially active, consider volunteering or getting involved
• Try to get the best medical care possible if something seems to be physically or
psychologically wrong. Ask your doctor to adjust medications that affect cognition.
• Correct even mild hearing or vision losses; reduced activity in the brain due to age-related sensory changes can lead to faster rates of atrophy and an increased risk of cognitive decline and dementia (Smith).
• Address sleep problems: if untreated they can affect the resilience of the brain (Ho).
• Eliminate alcohol consumption and tobacco use. (Daviet)
• Minimize stress
Widespread prioritizing of healthy habits will have a measurable impact on the future incidence of cognitive decline. Perhaps, hopefully, our grandchildren will learn whether improved brain health, supplemented by the development of targeted treatments and cures, will result in a decrease in the future risk of cognitive decline.
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