Background
Life expectancy at age 70 in the U.S. is 14 years, longer than in most other industrialized nations. Living long, however, does not necessarily mean living well. Disability is a major public health problem affecting more than one-third of older Americans and is a research priority of the NIA. Surprisingly little, though, is understood about pathobiologic pathways from independence to disability.
The intramural Laboratories of Epidemiology, Demography and Biometry (EDB) and Clinical Investigation are supporting a clinical research study, the Dynamics of Health, Aging and Body Composition (HEALTH ABC). This study, targeted to understanding the decline in function of healthier older persons, complements research efforts in prevention of functional decline for healthy and frail older persons by focusing on the substantial majority of older persons in transition from vigor to frailty.
The major objectives of the HEALTH ABC Study relate to observations that change in body composition in old age, particularly the increase in body fat and the decline in lean mass and bone mineral, represent a common pathway by which multiple diseases contribute to disability. There are many unanswered questions regarding the patterns and health impact of changes in weight and body composition in old age. Weight generally increases over the lifetime until late middle age, then tends to decrease into old age with changes in muscle, fat and bone. It has been postulated that the accelerated loss of muscle and strength in old age contributes to the onset of disability. Studies of weight and its relationship to mortality in older persons have yielded contradictory findings, leading to controversy regarding public health recommendations for weight in old age. Few studies have examined weight-related morbidity in old age, especially among African-Americans.
Goals
The HEALTH ABC Study will characterize the extent of change in body composition in older men and women, identify clinical conditions accelerating these changes, and examine the health impact of these changes on strength, endurance, disability, and weight-related diseases of old age. The study population consists of 3,075 persons age 70-79 at baseline with about equal numbers of men and women. Thirty-three percent of the men are African-Americans as are 46% of the women. All persons in the study were selected to be free of disability in activities of daily living and free of functional limitation (defined as any difficulty walking a quarter of a mile or any difficulty walking up 10 steps without resting) at baseline.
The principal goals of the HEALTH ABC are:
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To assess the association of baseline body weight, lean body mass, body fat, and bone mineral content, in relation to weight history, with:
- incident functional limitation
- incidence and change in severity of weight-related health conditions
- recovery of physical function after an acute event
- baseline measures of strength, fitness and physical performance
- gender, ethnicity and socioeconomic status
- To access the contribution of episodes of severe acute illness in healthier older persons to changes in body weight, bone mineral content, lean body mass and body fat, and the relationship of these episodes to risk of functional limitation and recovery.
- To assess the impact of weight-related co-morbid illness on the risk of functional limitation and recovery.
- To assess the ways in which physiologic mediators of change in body composition influence and are influenced by changes in health in older adults and contribute to change in body composition; to understand how changes in body composition affect weight-related cardiovascular disease risk factors such as lipids, blood pressure and glucose tolerance.
- To assess the interdependency of behavioral factors, such as nutrition and physical activity, co-morbid health conditions, and their association with change in body composition in old age.
- To provide a firm scientific basis for understanding issues related to weight recommendations in old age through increased knowledge of the potential trade-offs between weight and risk of functional limitation, disability, morbidity and death; to provide information critical for developing effective strategies for the maintenance of health in older persons.
Study design
The core yearly examination for HEALTH ABC includes measurement of body composition by dual energy x-ray absorptiometry (DXA), walking ability, strength, an interview that includes self-report of limitations, a medication survey, and weight (Measurements in the Health ABC Study). Provision has been made for banking of blood specimens and extracted DNA (HealthABC repository). Study investigators are open to collaboration especially for measures focused on obesity and associated weight-related health conditions including osteoporosis, osteoarthritis, pulmonary function, cardiovascular disease, vascular disease, diabetes and glucose intolerance, and depression.
For further information, see the Health ABC website - http://www.grc.nia.nih.gov/branches/ledb/healthabc/index.htm or contact: Tamara Harris, M.D., M.S. (NIA) harrista@nia.nih.gov or Eleanor Simonsick, Ph.D. (NIA) Simonsickel@grc.nia.nih.gov
