One consequence of the "graying" of the world's population is that psychiatrists, along with all health care professionals, will increasingly be providing services to older adults. In the United States, the first set of people belonging to the baby boom generation turned 60 in 2005, and the number of people older than 60 will soonoutnumber children for the first time in recorded history. The science of successful aging has recently emerged as a counterpart to the traditional focus of geriatrics, geriatric psychiatry, and gerontology on disease and disability.
Although no one phenotype of successful aging is yet agreed on, cognitive and emotional health in older adults are key ingredients to successful aging. As new ways of preventing or slowing morbidity from chronic physical illnesses emerge, brain health may become the primary "rate-limiting" factor in older age. Therefore, mental health practitioners can play a major role in enhancing the probability of successful aging. They will also increasingly treat individuals with chronic mental illnesses who are aging.
This article focuses on 4 main issues of successful cognitive and emotional aging:
- Definitions of successful or healthy aging.
- Biological mechanisms involved in cognitive and emotional health.
- Interventions to enhance successful aging.
- A summary of strategies for mental health practitioners to use in promoting healthy cognitive and emotional aging.
Defining phenotypes of successful aging
Longevity is one phenotype of healthy aging, but not an ideal one. Few people would care to live to age 90 years if it meant that they would experience Alzheimer disease and functional limitations and reside in a nursing home for many years. In their landmark article published in Science, Rowe and Kahn1 proposed that "successful aging" was on the upper end of a continuum, different from "normal aging" and "pathological aging." Their proposed phenotype of successful aging was differentiated from normal aging by the following characteristics: freedom from disease and disability, high cognitive and physical functioning, and engagement with social and productive activities.2
Since Rowe and Kahn proposed their model, there have been a number of studies that employed operationalized criteria to study successful aging. A critical review of this literature suggests a remarkable diversity in these operational definitions—in 28 studies using an operationalized criterion of successful or healthy aging, there were 29 different definitions.3 Most of these definitions included a dimension of physical functioning and/or disability. Other dimensions that appeared in fewer than half the definitions included cognitive functioning and social resources.
When definitions are restricted to cognitive and emotional health, excluding physical functioning, a high proportion of older adults can be classified as successfully aging. The majority of community-dwelling elderly people report that they are aging successfully, even though the majority would not be categorized as such in the model developed by Rowe and Kahn because of the presence of some chronic disease or functional limitation.4-6
In the Cache County longitudinal cohort study of memory, a population-based study of elderly persons living in Utah, 80% to 90% of the participants between the ages of 65 and 75 years and about 60% of those older than 85 years rated their health as good or better. Most were residing independently, had intact cognition, and engaged in social activities.7 Although the delineation between cognitive/emotional aging and physical aging is blurry, increasing attention has been paid to positive aging "from the neck up." This is exemplified by a recently convened work group commissioned by the NIH. The Cognitive and Emotional Health Project defined successful cognitive and emotional aging as "the development and preservation of the multidimensional cognitive structure that allows the older adult to maintain social connectedness, an ongoing sense of purpose, and the abilities to function independently, to permit functional recovery from illness or injury, and to cope with residual functional deficits."8
Defining positive states among people with mental health diagnoses is also an emerging science. Over the past decade, the focus in psychiatry has shifted toward the concept of "outcome," which is a more holistic concept than the mere absence or control of symptoms of mental illness. Older adults with schizophrenia and other psychiatric disorders do appear to attain "sustained remission" or "recovery." Despite assumptions that older age compounds the problems associated with psychiatric disorders, older age in schizophrenia appears to be negatively correlated with psychotic symptoms and positively correlated with health-related quality of life.9
Blazer10 noted that success in late life has been tied to success in managing disability. Hence it may be assumed that the idea of success being an integral part of the aging process is a new paradigm for psychiatrists. A challenge in measuring outcome has been to determine a global outcome measure. Several markers exist, but there is lack of consensus among them. For example, using the symptom remission criteria of Andreasen and colleagues,11 a sample of older patients with schizophrenia in New York demonstrated a 50% remission rate.12 However, using alternative criteria for clinical and social recovery (ie, living independently for 2 years, without a psychiatric hospitalization for the past 5 years, presently reported psychosocial functioning within the normal range confirmed by a caregiver), only 8% attained this level in a San Diego study.13
If greater consensus is attained, successful aging could be a useful outcome for older persons with chronic mental illnesses for several reasons. First, it is specific to older adults unlike several other measures that were developed in younger clinical populations. Second, it is a broad multidimensional construct. Third, development of a phenotype for successful aging will allow for a better understanding of the degree to which various dimensions of success are impacted by chronic mental illness. Finally, successful aging is a 2-pronged concept--it allows for measurement of outcome and promotion of health.14
The biology of healthy aging is a particularly rich area of study. Beginning with genes, we know from twin studies that about 20% to 40% of variation in the human life span is accounted for by heredity.15 Data suggest that in general, a longer life is made possible by the lack of harmful genes rather than the presence of life-extending genes.15 There are few studies that have examined the influence of genes on healthy aging phenotypes other than longevity. Glatt and colleagues16 reviewed 28 studies that examined genes and their relationships to multicomponent definitions of healthy aging--genes that emerged from this review appear to be related to disease processes (eg, apolipoprotein E [APOE]), inflammation (interleukin-6), and metabolism. Genes are thus likely to impact the probability of aging successfully, and once associations are established, the mechanisms for their effect can be explored.16
In addition to examining genetic influences via case-controlled studies, research has recently examined gene/ environment interactions. For instance, in the MacArthur Study of Successful Aging, having a greater educational attainment appeared to dampen the effect of the APOE4 gene on risk of cognitive decline.17 Therefore, people may be able to buffer the risks associated with specific genes through modifying environmental factors.
At the cellular level, stress resistance may play a key role in determining successful aging. A growing body of literature has linked environmental stress to negative physiological changes. Allostatic load provides an indication of the degree of chronic stress-related activation. By combining a number of indicators of stress derived from cardiovascular and neuroendocrine assays it provides an indication of the degree of overactivation of the hypothalamic- pituitary-adrenal (HPA) axis and the sympathetic nervous system. According to the MacArthur Study of Successful Aging, higher allostatic load appears to increase mortality in aging people who were initially classified as successfully aging,18 and a reduction in allostatic load appears to reduce mortality risk.19 Therefore, it is likely that healthy aging may depend on the degree to which older people are resistant to the negative effects of stress, whose environments produce fewer stressful events, and/or who have psychosocial attributes that buffer stress, such as social support and optimism).
Beyond genes, neuroscientists have examined relationships between maintenance of cognitive health and the structure and function of the brain. Two areas of research that have great relevance to successful cognitive aging include the concept of cognitive reserve and the study of neuroplasticity. Cog- nitive reserve posits that the more "developed" a brain is on entering older age, the longer it will take to cross the threshold of impairment. Key ways to attain cognitive reserve are to attain a high level of education, engage in mentally stimulating occupations, and perform mentally challenging activities.20
However, cognitive reserve obtained in earlier development is not the sole pathway to successful cognitive aging, because the brains of laboratory rats and humans show a remarkable capacity to reorganize in order to maintain processing efficiency. In aging rats, maintenance of long-term potentiation (eg, memory) appeared to involve a switch in N-methyl-d-aspartate receptor characteristics, indicating that the aging brain reorganized to facilitate a capacity for continued learning.21
Understanding the mechanisms of reorganization and plasticity in aging may enable a new breed of intervention. Thus, the mechanisms of successful aging are intensely complex, involving interactions between genes, brain, and environment, along with attitudes and beliefs. We now turn to what can be done to enhance the probability of successful aging.
Short of a fountain of youth, there are a number of modifiable aspects of aging that lend themselves to healthy aging interventions; chief among them are physical activity, nutrition, and mental activity.22 Perhaps the single most potent and accessible is physical activity; exercise boosts physical function, reduces risk of falls, and may likely improve cognitive functions as well. Benefits may be obtained by exercise initiation even among those who are already older adults.
A recent meta-analysis of 18 randomized controlled trials of exercise interventions (eg, walking, strength or resistance training) conducted in older people without dementia23 showed that the mean effect size was 0.48 across measures of cognitive functioning in favor of exercise. The largest effect was seen in the executive functioning domain (eg, planning), which, along with memory, is highly related to everyday functioning in older people. A randomized controlled trial that compared physical exercise with sertraline in the reduction of depressive symptoms in older adults indicated that both interventions reduced depression to a roughly equivalent degree.24
There are a number of putative mechanisms by which exercise exerts positive health effects in later years. Reducing cardiovascular risk may limit the number of microscopic lesions that occur in the brain, along with reduced wear and tear on joints due to obesity. At the cellular level, exercise may provide a mild stressor that acts as a kind of "inoculation" against other kinds of stress.20 Exercise may also have a secondary association with increased frequency of social contact. Given that exercise is typically inexpensive, associated with few risks in most circum-stances, and has such profound benefits, its prescription seems nearly universally warranted.
In animal models of aging, the single most effective intervention to date in terms of lengthening life span turns out to be caloric restriction. Rodents can live up to 40% longer when subjected to a calorically restricted diet, and extension of the life of primates is also possible with caloric restriction (although not to the same extent).25 It is theorized that the mechanism of caloric restriction is in reducing the rate of metabolism of glucose, perhaps limiting cellular wear and tear.25 Outside of caloric restriction, longitudinal studies of aging individuals classify a low-risk diet as one that includes a higher ratio of polyunsaturated to saturated fats. Also, it is high in cereal fiber and marine fatty acids and low in glycemic load and should include a multivitamin.26 In addition, moderate alcohol consumption (1 drink per day) appears to be better than not drinking.27
It is commonly held that engaging in cognitive activities, such as crossword puzzles, can build cognitive reserve to delay or decelerate cognitive decline. There is now evidence that cognitive abilities can be improved in older age using formal structured cognitive training. Cognitive training can be divided into restorative (repairing deficits) or compensatory (adapting behavior or the environment to circumvent deficits). The largest randomized controlled trial is the recently completed Cognitive Trial for Independent and Vital Elderly (ACTIVE), which enrolled more than 3000 older adults in multiple academic research centers across the United States.28 In the ACTIVE study, participants were randomized into one of several interventions, each one emphasizing a different cognitive domain (eg, executive functioning, memory). These interventions involved 10 to 18 hours of computerized training. Greater improvement was seen on neuropsychological tests than in day-to-day functioning at follow-up, but there were some significant improvements seen in functioning that were preserved 5 years after the study ended. More compensatory (versus restorative) approaches to cognitive training include those that make effortful processes (eg, arranging medications) more "automatic," such as through using implementation plans.29 Compensatory approaches assume that older adults can maintain functioning through habits and environmental supports that reduce the load on working memory.
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