Of all the consequences of aging, a diagnosis of Alzheimer's disease is perhaps one of the most dreaded. The most common form of dementia, Alzheimer's affects approximately 45 million people worldwide; because of the aging populations of North America and western Europe, this number is estimated to increase to more than 135 million in the year 2050.
With fears of an epidemic looming on the horizon, drug companies have been scrambling for a cure, pouring astronomical amounts of money into research and development of drugs that can effectively slow or stop progression of the disease. So far, however, their efforts have been fruitless: hundreds of compounds have shown potential in animal studies, only to fail when subsequently tested in humans [See: Why Do All the Large Alzheimer's Drug Trials Fail?]
Companies continue their search nevertheless, driven by the huge profits that an effective treatment would generate and by the belief that the drugs would work if patients were diagnosed and treated earlier. But many studies published in the past decade or so strongly suggest that certain lifestyle choices could be far more effective than any pharmacological intervention, even if it were found to work, in staving off Alzheimer's and other forms of cognitive decline.
The emerging picture is that a healthy diet and good sleeping pattern, as well as regular physical and mental exercise, all contribute to overall brain health and reduce one's risk of developing neurodegenerative diseases later in life. Research shows that education can to some extent protect the brain against Alzheimer's, and now it seems that having purpose in one's life can do so, too.
What's the meaning?
Purpose in life is regarded as one of six core dimensions of psychological well-being, along with autonomy, environmental mastery, personal growth, positive relationships, and self-acceptance. People are said to have purpose in life when they can describe specific goals and objectives that give them a sense of directedness and meaning.
The first study to specifically examine the link between purpose in life and Alzheimer's, led by neuropsychologist Patricia Boyle of the Rush University Medical Center, was -published in 2010. Boyle and her colleagues recruited over 900 elderly but otherwise healthy residents from nursing homes in the Chicago area, assessed their cognitive abilities, purpose in life and various other psychological and social measures, and followed them up every year for seven years.
During that time, 155 of the study participants developed Alzheimer's. Those who scored highest on the purpose in life scale were more than twice as likely to be disease-free than those who scored lowest. Greater purpose in life was also associated with a reduced risk of mild cognitive impairment and a slower rate of normal, age-related decline in cognitive function. This held true even when other potentially complicating factors, such as depressive symptoms, neuroticism, and the size of participants' social networks, were taken into account.
Boyle and her colleagues subsequently showed that purpose in life also reduces the effects of Alzheimer's pathology on cognitive function. Having purpose in life seems to protect the brain by building its reserve, making it better able to compensate for the damage inflicted by the disease, or to use alternative neural pathways more efficiently, to maintain a higher level of cognitive function for longer. [See: The Neuroprotective Effects of Education]
"Our studies show that purpose protects not only against Alzheimer's, but also against risk for mortality and disability," says Boyle. "The basic idea we're working with is that it somehow provides functional resilience in the face of multiple diseases. One of the things we're looking at now is if purpose in life can help people in the face of stroke."
Research also shows that gaining some kind of purpose later on life can have real benefits. In one recent study, for example, Michelle Carlson of Johns Hopkins University and her colleagues recruited 149 older adults and randomly assigned them to one of two groups.
Participants in one group were enrolled in the Experience Corps, a community-based program that trains older adults to act as literacy tutors for struggling public schools students; each adult spent 15 hours per week during one academic year helping elementary school children. Those in other group were told that they had been put onto the waiting list for the program, and continued with their largely sedentary lifestyle for the duration of the study.
All of the participants performed various neuropsychological tests at the beginning of the study and repeated the same tests at the end. Those who had taken part in the Experience Corps program performed better the second time around, whereas those who hadn't did worse.
A smaller follow-up study showed that these changes are associated with differences in brain activity. The researchers recruited 24 poor, undereducated African Americans living in nursing homes and deemed to be at high risk of mild cognitive impairment and Alzheimer's, and enrolled some of them in the Experience Corps program, serving as volunteers in three kindergartens in Baltimore.
Again, the participants performed cognitive tests at the start and end of the study. This time the researchers used functional magnetic resonance imaging (fMRI) to record the participants' brain activity during the tests. They found that those who had taken part in the program outperformed those who had not on tests of executive function, and that this was associated with increased activity in the left prefrontal cortex and anterior cingulate gyrus.
Motivated to succeed
"It may be helpful to think about purpose in life in terms of motivation and environmental enrichment," says neurologist Nick Ward of University College London, who uses functional neuroimaging to investigate how reorganization of brain networks in the cerebral cortex support the recovery of arm function in stroke patients.
"People who are more motivated tend to recover better after a stroke," he adds, "and we know very well from animal studies that environmental enrichment enhances neuronal plasticity."
Boyle doesn't doubt that these factors are involved. "Someone who is purposeful is much more motivated to reach their goals," she says. "They're getting out there, and in the process are getting exposed to new environments, opportunities, and learning experiences."
She emphasizes the difficulties in extricating the effects of purpose in life from those of other, related factors, but thinks that it can be done, and that purpose may have a real, physiological, effect on the brain. "It's an extremely complex trait that probably works on multiple levels. But even after controlling for as many of these other factors as we can, we still see a robust effect, and what we'd really like to understand is the underlying biology."
One provocative study published last year points to a possible biological effect: It showed that eudemonic well-being, which one gets from being virtuous, is associated with decreased expression of various stress-related genes in human immune cells, whereas hedonic well-being had the opposite effect.
Ralph Waldo Emerson may have been onto something, then, when he said: "The purpose of life is not to be happy. It is to be honourable, to be compassionate, to have it make some difference that you have lived and lived well."