Theories of Aging

1. Theories of Aging Min H. Huang, PT, PhD, NCS

2. Course Objective • Explain the concepts related to contemporary biological and psychosocial theories of aging. • Adapt examination and plan of care for the geriatric patient based on psychosocial and cultural characteristics of the patient.

3. Reading Assignment • Guccione: Ch3 (pp. 27-29) • Aldwin & Gilmer 2013. http://books.google.com/books?id=uevNZepnQm4C&lpg=PP2&ots=txH5z84yCt&dq=Psychosocial%20theories%20on%20aging&lr&pg=PR8#v=onepage&q&f=false. pp. 52-55

4. Factors contributing to age-related declines in physiological systems • Whole-body inflammation, rather than biological wear and tear based on genetic programming alone, contribute to age-related declines • Genetic accounts of about half of the decline • Lifestyle accounts for the other half, e.g. • Physical inactivity (primary factor) • Inadequate nutrient intake • Smoking • Excessive alcohol intake

5. Aging: a decline in homeostasis • Homeostasis: physiological processes that maintain a stable internal environment of the body • The range of homeostasis increases in response to exercise, and decreases with the addition of chronic disease & inactivity • Awidening window of homeostasis increases tolerance to physiological stress, thus reduce the possibility of moving out of homeostasis into death

6. Physical stress theory (PST) -- Mueller and Maluf 2002. PTJ. • Changes in the relative level of physical stress cause a predictable adaptive response in all biological tissue. http://ptjournal.apta.org/content/82/4/383.full.pdf

7. Biological tissues exhibit 5 adaptive responses to physical stress. Specific thresholds define the upper and lower stress levels for each adaptive tissue response. The relative relationship between the thresholds is fairly consistent between people. The absolute values for thresholds vary greatly.

8. Prolonged physical stress levels that are lower than the maintenance range result in decreased tolerance of tissues to subsequent stresses (e.g. atrophy).Injury (and all other adaptations) occurs at a lower level of physical stress than required previously.

9. Prolonged physical stress levels that are higher than the maintenance range result in increased tolerance of tissues to subsequent stresses (e.g., hypertrophy). Injury (and all other adaptations) occurs at a higher level of physical stress than required previously.

10. Range of homeostasis tolerance and ability to adapt to stress

11. Theories of aging • Biological theories of aging • Explain the aging process from the anatomic and physiologic perspectives • Involve physical structures and functions • Psychosocial theories • Explain the thought processes, psychological, and behaviors changes with aging

12. Biological theories of aging • Programmed theories • aging follows a biological timetable that regulates growth and development • this regulation depends on changes in gene expression that affect the systems responsible for maintenance, repair and defense responses • Damage or error theories • emphasize environmental assaults to living organisms that induce cumulative damage at various levels as the cause of aging Jin 2010. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2995895/

13. Programmed theories of aging • Programmed longevity theory • Aging results from a sequential switching on and off of certain genes • Endocrine theory • Aging is hormonally regulated • The insulin/insulin-like growth factor 1 pathway plays a key role • Immunological theory • The immune system is programmed to decline over time, which leads to an increased vulnerability to infectious disease and thus aging and death.

14. Damage or error theories of aging • Wear and tear theory • Cells and tissues have vital parts that wear out resulting in aging • Rate of living theory • The greater an organism's rate of oxygen basal metabolism, the shorter its life span • Cross-linking theory • An accumulation of cross-linked proteins damages cells and tissues, slowing down bodily processes resulting in aging

15. Damage or error theories of aging • Somatic DNA damage theory • DNA damages occur continuously in cells. While most of these damages are repaired, some accumulate. • Genetic mutations occur and accumulate with increasing age, causing cells to deteriorate and malfunction. • Free radicals theory • Superoxide and other free radicals cause damage to the macromolecular components of the cell • Accumulated damage causing cells, and eventually organs, to stop functioning

16. P53: a tumor suppression protein ROS: reactive oxygen species is a toxic intermediate Unified biological theories of aging – Kelly, 2011. Nature. 470:342-343.

17. Caloric restriction (CR) on aging • Caloric Restriction decreases formation of free radicals within the mitochondria • Increase the antioxidant defense capacity • Proportionally more body fat is lost than any other tissue with CR diet • Mice on a 35% CR diet lost 70% of total body fat • CR induces key shifts in genes involved in metabolism in WAT • The expression of more than 50 pro-inflammatory genes is reduced

18. Caloric restriction (CR) on aging • The overt changes induced in WAT (white adipose tissue) by CR may contribute to alterations in systemic metabolic homeostasis Anderson & Weindruch. 2012. American Journal of Human Biology, 24:101–106.

19. Current psychosocial theories of aging • Selective Optimization with Compensation Theory • Socioemotional Selectivity Theory • Cognition and Aging Theories • Personality and Aging Theories

20. Classic theories: ontogenetic models • Developmental force is internal and biologically based • Developmental stages are universal, sequential, and irreversible • Universal: applicable to everyone • Sequential: follow a definite order • Irreversible: development represents achievements

21. Life course theory (Elder 1974) • Development is a series of transitions and choice points that are influenced both by • Immediate social context • Larger sociohistorical period (i.e. cohort) • Gender and social roles • Intergenerational Study • Followed children born in 1920s-30s into late life • Children from economically-deprived, working class families had very difficult, chaotic lives • Children from economically-deprived, middle-class families did better than non-deprived peers

22. Goal-oriented models: life span theory (Baltes 1987) • Development in adulthood is a balance between gains and losses • More gains in early adulthood and more losses later • Successful aging is an adaptive process to aging, i.e. SOC • Selection • Optimization • Compensation

23. Goal-oriented models: Self development model (Brandtstädter 1999) • There are developmental changes in goals from young adulthood to late life • Goals in young adulthood • To achieve ideal self • Largely culturally determined • Goals in late life • To maintain self as much as possible • To preserve resources and counteract losses

24. Self-directed development (Langer 1990) • Development is something that individuals do, with increasing mindfulness • Mindfulness • Continuous creation of new categories • Openness to new information • An implicit awareness of more than one perspective • Mindlessness • Entrapment in old categories • Autonomic behaviors • Awareness of only a single perspective

25. Self-directed development: liberative model (Levenson & Crumpler 1996) • Development is an increasing freedom from social and biological conditioning based on self-observation • One becomes aware of negative characteristics that can limit one’s choices of action • Losses force individuals to examine their own assumptions and develop new and more mindful ways of being • Basis of gerotranscendence in late life • Recognition of death influences the development of a “decentered” perspective in late life

26. Resilience and aging • Resilience is the developmental process of being mindful of and prioritizing those behaviors, thoughts, and feelings that facilitate contentment within a specific developmental, physical, emotional and spiritual context (Allen et al. 2011) • Resilience is the process of optimizing opportunities for health, participation and security in order to enhance quality of life as people age (WHO 2002)

27. Resilience and aging: dynamic model of affect (DMA) (Zautra et al. 2010) • Positive and negative affect are generally orthogonal • Positive and negative affect become inversely associated under stressful conditions • Resilient individuals are more likely to maintain orthogonal positive and negative affect under stress

28. Resilience and aging: emotional regulation (Charles 2010 & Aldwin 2007) • Older adults are better at regulating emotions • Possible from long-term experience with various stressors in life • Older adults have greater clarity in the relative importance of problems • Only a finite time left following the loss of loved ones • Appraisal of stress is generally lower in older adults than in younger adults • Larger perspective and positive coping strategies gained from dealing with prior stressors

29. An ecological model of resilience (Aldwin & Igarashi 2012)

30. Summary • Current psychosocial theories emphasize on conscious choices in developmental processes • Lifestyle choices can impact health and the development of diseases and consequently, accelerate or decelerate the aging process • Resilience in late life – how older adults maintain emotional stability despite of the physical and psychosocial losses – is central to optimal aging.