A Life Course Approach to Healthy Aging, Frailty, and Capability

Abstract

OVER the last 25 years, investment in aging research has been greater in the United States than the United Kingdom, particularly in population studies investigating healthy aging or frailty and their determinants, or cohort changes in health and functioning. It is still unclear, in the U.K. context, whether age-related declines in health and functioning of cohorts now in late middle age will differ from that of current older people, and whether socioeconomic and gender differences in aging and expectations of life at older ages are changing. In 2005, a House of Lords scientific report on aging (1) called for new research to address these questions with a focus on the underlying lifetime process of biological aging that could integrate the rather separate research on specific age-related diseases, and translate evidence into policy and practice. Investment in U.K. aging research is beginning to change. Healthy aging has become a preoccupation of the British government. For example, the U.K. Treasury, as part of the 2007 Spending Review, highlighted aging as one of the Grand Challenges faced by the U.K.; it is concerned with the economic and social consequences of the rapid increase in the old age dependency ratio as the baby boom generation reaches retirement age (2). There are calls for a step change in multidisciplinary research to understand healthy aging and how to maintain a population that remains healthy and productive longer (3). Policymakers recognize that healthy, independent, and active aging not only enhances individual lives but also addresses the social and economic implications of an aging population, and relieves pressure on public spending (4). U.K. research councils are making available new funding streams for aging initiatives, often spanning several councils, to address these concerns. The New Dynamics of Ageing research program (5) and the recent call for Medical Research Council Centres for Lifelong Health and Wellbeing (6) epitomize the growing interest in multidisciplinarity, life course approaches to aging, and expectations for knowledge transfer and user engagement. These calls for research highlight the consensus that the aging process operates from the beginning of life, driven by the rate of accumulation of molecular and cellular damage. Growing evidence from life course and historical cohort studies that adult function and age-related chronic diseases have their origins in early life experience and share common risk factors and causative mechanisms support this consensus (7,8). Modifiable factors such as nutrition and activity and chance events acting across the life course can alter exposure to sources of damage and the effectiveness of body systems for maintenance and repair (9). While genes have traditionally been seen as a nonmodifiable factor, there is growing evidence linking epigenetic DNA modification through environmental exposures to a wide range of aging phenotypes. This focus on early life and life course determinants of aging is stronger in the U.K. than the U.S. It partly arises from greater opportunities in the U.K. to capitalize on the maturing birth cohort studies and the historical cohort studies that have imaginatively linked development and early environment to later health outcomes (10,11). Investigators of maturing birth cohort and aging cohort studies increasingly share a common interest in characterizing aging trajectories and the extent of variation between individuals and across gender or social groups. They are interested in how dynamic relationships between different aging trajectories unfold over time and the common mechanisms or sources of risk, and in relating aging trajectories and their determinants to disease incidence, quality of life, and survival. The advantage of birth cohort studies is that they permit exploration of how biological, psychological, and social risk factors or risk factor trajectories, acting independently, cumulatively, or interactively across the whole life course, influence aging trajectories. This growing focus on life course determinants of aging has implications for studies of capability, the mechanisms of biological aging, and the clinical syndrome of frailty.