Successful aging was differentiated from normal aging by the following characteristics:
- freedom from disease and disability
- high cognitive and physical functioning
- engagement with social and productive activities.
increasing attention has been paid to positive aging “from the neck up.” 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
- the abilities to function independently
Success in late life has been tied to success in managing one’s disabilities.
20% to 40% of variation in the human life span is accounted for by heredity. In general, a longer life is made possible by the lack of harmful genes rather than the presence of life-extending genes. For instance:
- MacArthur Study of Successful Aging, having a greater educational attainment appeared to dampen the effect of the APOE4 gene on risk of cognitive decline.
- 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 stress appears to increase mortality in aging people who were initially classified as successfully aging
- Reduction in stress appears to reduce mortality risk (it also helps cognitive functioning so financial decision-making)
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.
- Cognitive 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: 1) attain a high level of education, 2) engage in mentally stimulating occupations, 3) perform mentally challenging activities.
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.
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.
… 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.
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.
- 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 circumstances, 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). It is theorized that the mechanism of caloric restriction is in reducing the rate of metabolism of glucose, perhaps limiting cellular wear and tear.
Compensatory approaches assume that older adults can maintain functioning through habits and environmental supports that reduce the load on working memory.
Given the literature on stress and the importance of stress resistance in cellular aging, stress reduction may provide benefit in older people.
Late-life depression, for example, reduces the likelihood that an individual will engage in preventative health behaviors, such as physical activity and socialization; may relate to cellular aging through diminished stress resistance; is associated with diminished level of optimism; and can impair cognitive functioning. However, late-life depression is treatable, and successful detection and intervention by mental health providers can thus produce a far-reaching impact.