For good reason. One in eight adults over 65 is affected by the disease. Those who are spared know they may end up with the burden of caring for a parent or a spouse who is affected. Even though the number of older adults with dementias is rising rapidly, only a few drugs that have been approved to treat symptoms are on the market, and they slow down the disease but do not cure it.
Researchers, however, are more optimistic than ever about the potential of the aging brain, because recent evidence has challenged long-held beliefs by demonstrating that the brain can grow new nerve cells.
“For a long time, we held the assumption that we’re born with all the nerve cells we’re ever going to have, and that the brain is not capable of generating new ones — that once these cells die we’re unable to replace them,” said Molly V. Wagster, chief of the Neuropsychology of Aging branch of the National Institute on Aging. “Those assumptions have been challenged and put by the wayside.”
The birth of new nerve cells, she said, “has been shown to occur in the adult — not only in adult rats and monkeys, but also in older adult humans.” Most of the areas that show neurogenesis and that have been investigated so far are important for learning and memory, particularly the hippocampus, she added.
So how does one stimulate neurogenesis?
Scientists do not have all the answers, but studies of older people who have maintained their mental acuity provide some clues. They tend to be socially connected, with strong ties to relatives, friends and community. They are often both physically healthy and physically active. And they tend to be engaged in stimulating or intellectually challenging activities.
The big question is whether they remain mentally alert because they engage in these activities, or whether they are able to engage in these activities because they are cognitively intact.
“We don’t know whether this is an example of reverse causation or not — it’s probably a two-way street,” said Bruce S. McEwen, who heads the neuroendocrinology lab at Rockefeller University in New York.
But some interventional studies that have introduced older adults to exercise regimens have reported remarkable results. Researchers at the University of Illinois at Urbana-Champaign recruited a group of sedentary adults between the ages of 60 and 75, assigning half of them to an aerobic exercise program that met three times a week to walk, while a control group did anaerobic stretching and toning.
The scientists measured the group’s cognitive function before and after the six-month program and found improvements among those who had done the walking.
“Six months of exercise will buy you a 15 to 20 percent improvement in memory, decision-making ability and attention,” said Arthur F. Kramer, a professor of psychology at the University of Illinois. “It will also buy you increases in the volume of various brain regions in the prefrontal and temporal cortex, and more efficient neuronetworks that support the kind of cognition we examined.”
Other studies have found improvements in cognitive function after a combined regimen of physical exercise and cognitive training.
But skeptics say there is no guarantee that intellectual stimulation will prevent Alzheimer’s disease or other forms of dementia. “Maybe it does, but I don’t think we have a shred of evidence,” said Dr. Robert N. Butler, a psychiatrist and gerontologist who is president of the International Longevity Center-USA. “What it does is maintain good health,” he said, adding, “I don’t think we can go much further than that.”
But there is consensus among scientists on a few recommendations for action that, most agree, cannot hurt.
Regular physical activity may improve brain function, both by increasing blood flow to the brain and stimulating the production of hormones and nerve growth factors involved in neurogenesis. Animal studies have found that physically active animals have better memories and more cells in their hippocampus. Exercise also plays a role in countering diseases like Type 2 diabetes, which increases the risk of dementia. Cholesterol and hypertension, which affect vascular health, also need to be kept in check.
Seeking out stimulation through interesting work, volunteer opportunities or continuing education is beneficial. Travel, read, take up a new language or learn to play a musical instrument. Staying socially connected is also associated with brain health, as is managing stress effectively. Chronic stress can lead to the rewiring of areas of the brain that are involved in emotion, memory and decision-making, Dr. McEwen said, “and the brain becomes more biased toward more anxiety, more depression, less flexibility in terms of decision-making and becomes less able to store information.”
Most scientists recommend eating a Mediterranean-style diet, including fish and nuts containing omega-3 fatty acids, antioxidant-rich fruits and vegetables, olive oil and possibly some red wine. (Blueberries are also recommended.) Some also suggest avoiding playing games like football, because of the risk of head injuries, staying away from pesticides and insecticides that contain neurotoxins and not drinking excessively.
“Another thing that’s important as people get older is to maintain flexible attitudes and be willing to try new things,” said K. Warner Schaie, who in 1956 started the Seattle Longitudinal Study, which follows the psychological development of participants through adulthood. “You have to expect things will shift over time and won’t be the same as when you were young. Those who manage to roll with the punches, and enjoy change rather than fighting it, tend to do well.”