Rowe and Kahn [1
] proposed criteria for successful aging comprised of avoidance of disease, maintenance of high cognitive and physical function, and sustained engagement in social and productive activities. This model grew from highly prolific MacArthur Foundation Study of Successful Aging, a $10 million, 10-year research effort led by Rowe and Kahn. The objectives of this study, and the theoretical framework that grew from it, are to better understand risk factors for decline and to inform prevention efforts. For instance, work drawn from this initiative concluded that pulmonary health relates to both gross motor and cognitive functioning in late life, suggesting this as an area for primary intervention in preserving late-life independence [2
]. Drawing on the MacArthur Study data, Others have investigated modifiable risk factors for dementia, concluding that late-life depression may be a precursor of cognitive decline [3
]. Still other work based in this study found that older adults who frequently felt useful to others had lower rates of disability and mortality than less-engaged elders, emphasizing the importance of social engagement and productive activities [4
]. While support for this theory of successful aging has been mixed [5
], it provides a useful framework for examining longevity. This paper will examine whether the Rowe and Kahn successful aging variables are each independently related to longevity. In the current paper we chose to examine this theory in older old women over 80 years. Women constitute a majority of all older adults over 80 but more importantly, they are more likely than men to experience disability and to live more years with disability than men [7
]. Geriatric syndromes such as cardiovascular disease, cognitive decline, and depression compromise functional independence more with increasing age [8
]. Age 80 represents a point when medical treatment planning for elders should be reevaluated given the escalating risks associated with these comorbidities.
Behavioral factors as defined in this paper include psychological aspects of functioning that can be measured through self-report or performance-based assessment, such as mood and cognitive functioning (i.e., depression and cognition). Important behavioral factors such as cognition and depression represent major risk factors for disability, often preceding disability [9
] and possibly reducing longevity. Serious disability, especially mobility loss, has been linked to reduced survival [10
]. Identifying behavioral factors that hasten disability onset may then lead to improved models of integrated care. Behavioral factors such as depression and cognitive decline may best be understood when integrated with chronic disease, especially those that enhance vascular risk.
Though Rowe and Kahn interpreted “avoidance of disease” broadly, vascular disease is particularly significant to healthy aging as these chronic conditions (e.g., hypertension, atrial fibrillation, and diabetes) gradually compromise adaptive resources. Neural network functioning is broadly compromised by the effect of vascular disease on cerebral tissue, termed cerebrovascular burden (CVB). CVB is also associated with higher stroke risk, cardiac disease, and sensorimotor impairment. Moreover, high CVB hastens the manifestation of clinically significant cognitive impairment, regardless of the specific etiology of cognitive decline (e.g., normative aging, Alzheimer's disease, Parkinson's disease, and vascular dementia) [11
]. Elders with high CVB tend to have less prefrontal white matter volume, more white matter hyperintensities, and comparably impaired executive functioning [12
]. Considerable evidence also exists that CVB also contributes to the development of late-life depression symptoms [13
]. Thus, in addition to being a broad measure of physical health in the Rowe and Kahn model, inclusion of CVB will distinguish variance in mortality risk directly related to this variable, thereby providing a more stringent test of how depression and cognition independently relate to longevity.
Successful aging theory identifies sustained engagement in social and productive activities as central to healthy aging. Clinical depression throughout the lifespan is characterized by reduced enjoyment in activities and decreased social engagement. As such, depression symptoms in late life represent a significant barrier to successful aging based on this interpretation. Generally speaking, more depression symptoms translate to poorer health outcomes. For instance, people experiencing depression are at greater risk of a first heart attack [15
], stroke [16
], cancer [18
], worse health outcomes after controlling for cardiovascular risks [15
], and higher mortality [19
]. Depression in later life was found to be a significant risk factor for death. Mehta et al. [20
] reported that, in a large sample of community-dwelling elders, mortality was significantly predicted by both number of depressive symptoms and performance on a measure of cognitive functioning. Similarly, it was reported that in a sample of older patients with debilitating or chronic medical diagnoses, after controlling for age, comorbidity and illness severity, functional impairment and cognitive functioning, depressed respondents were 34% more likely to die over three years [21
]. In a large (N
= 3065) Dutch sample of individuals between the ages of 55 and 80, depression was identified as a significant risk factor for death over four years. However, the strength of this effect was partially eroded by the addition of other variables such as chronic disease, smoking, and physical inactivity [22
The third domain of successful aging theory identifies preservation of cognitive and physical functioning as critical to successful aging. Cognitive impairment limits quality of life by reducing the capacity for meaningful work and social interaction [23
], and rapid loss of cognitive faculties often suggests medical decline with a heightened mortality risk [22
]. Terminal cognitive drop is identified as an accelerated loss of cognitive functioning preceding death [24
], by contrast to terminal decline which is a linear decline function preceding death [25
]. A review from 2002 concluded that, largely because testing terminal drop theory requires a repeated-measures design, limited data existed supporting this theory [26
]. Since this review, several longitudinal studies have been published, including a recent study concluding that elders with sharp declines on the Minimental State Exam [27
], a brief cognitive screening measure, experienced more activity of daily living (ADL) disability and higher mortality rates than elders with more stable scores [28
]. While estimates of the temporal relationship between terminal drop and death vary, recent research identified evidence of terminal drop at a mean of 42 months before death [29
] in a large sample of dementia-free elders. These estimates are roughly similar to the original estimates of about 5 years reported by K. F. Riegel and R. M. Riegel [24
]. Similarly, past work drawing on the Health and Retirement Survey (HRS) data identified a relationship between cognitive impairment and mortality over a 2-year interval [30
]; however, this study evaluated cognitive decline cross-sectionally and did not include other markers of decline such as CVB or depression. Of note, Langa et al. reported evidence of compression of cognitive morbidity; elders with moderate or severe cognitive impairment in 2002 had greater risk of death over 2 years than those with similar levels of impairment in 1993.
Comorbid cognitive impairment and depressive symptoms suggest particularly high risk of death [19
]; however, these studies evaluated cognitive functioning cross-sectionally. While impairment on cognition measures suggests
decline from demographically representative norms, the concept of terminal cognitive drop specifies rapid loss of cognitive functioning over a brief period of time. Relatively few studies relating to cognition and longevity evaluate how decline over brief periods relates to longevity, and even fewer investigate whether depression and cognitive decline are independent predictors of mortality. Because cognition and mood, domains in which impairment may be most evident to family and medical practitioners alike, tend to be interrelated in late life [31
], it is important to distinguish the individual relationships of these variables with longevity.