Introducing the Health ABC Study: The Dynamics of Health, Aging, and Body Composition
The Health, Aging and Body Composition Study is an interdisciplinary study focused on risk factors for the decline of function in healthier older persons, particularly change in body composition with age. The study was designed to address differences in onset of functional limitation, disability and longevity between older men and women as well as between Blacks and Whites.
The factors contributing to change in body composition, including weight-related conditions, other age-related conditions, and behavioral and physiologic determinants are complex and interactive, resulting both in changing body composition and declines in health. Health ABC was meant to examine the inter-relationships of these factors in community-dwelling older persons. It was thought that the design of the study with the focus on multiple health conditions, would allow an assessment of multi-morbidity in declining function and in health care utilization.
Objectives: To investigate the hypothesis that change in body composition is a common pathway through which weight-related health conditions and behavioral factors contribute to functional decline and loss of independence in older persons.
Methods: A longitudinal cohort was recruited in 1997-98 consisting of 3,075 men and women, aged 70-79 at baseline; 45 percent of the women and 33 percent of the men are African-American. The cohort members were selected at baseline to be free of difficulty walking 1/4 mile or difficulty climbing up 10 steps. The major outcome of the study was persistent difficulty performing either or both of these two activities over two consecutive 6-month follow-ups.
There were yearly clinic examinations for six years with phone calls alternating every 6 months to update functional and health status. The phone calls continued every 6 months and additional examinations took place at follow-up years eight and ten. In addition, the study collected data and adjudicated major incident health events including cardiovascular events, cancers, fractures, dementia, diabetes, and other illnesses related to hospitalizations and medical expenditures. Follow-up was extended to 16 years. Semi-annual telephone interviews and adjudication of select disease events and deaths continued during this period. In Year 16, there was a continued exam with core study measurements in Memphis and a leg muscle biopsy examination in Pittsburgh.
The Health ABC clinic examination included a core of measurements on body composition, strength and function, with additional measurements for specific ancillary studies or to complement other measurements in the study (See Datasets/Documentation, Schedule of Exam Measures and Schedule of Questionnaire Measures. Some of these ancillary studies have included measurement of knee osteoarthritis with magnetic resonance imaging and a follow-up, funded by NIAMS, the Cognitive Vitality Substudy which focused on maintenance of cognitive function with aging, and an energy expenditure study (funded by NIDDK with a follow-up funded by NIDDK, CDC, NIA and NIMHD), in which doubly-labeled water and resting metabolic rate were used to assess level of physical activity, pulmonary function measurement funded through an R01, and a peripheral nerve function study (with follow-up at Year 11 for the whole cohort (funded by an NIA RO1). An MRI of the brain and additional mobility assessment was added in a subgroup through a grant funded by an NIA K-award. From Year 15-17 we conducted quarterly telephone interviews on health status as part of a grant from NINR regarding end of life decision-making.
The Health ABC Study was initiated and developed in the Intramural Research in the Laboratory of Epidemiology and Population Sciences. The study was conducted through research contracts with the Coordinating Unit at University of California, San Francisco and the field centers, University of Pittsburgh, and University of Tennessee Health Science Center, Memphis. This study has refined the recruitment and retention strategies for cohorts of elders; developed, tested, and applied novel methodologies to assess weight-related health conditions, functional capacity, impairment status, and sub-clinical pathology; and has expanded the scientific opportunities for ancillary studies, particularly in the areas of molecular and genetic markers. The opportunity to explore novel genetic risk factors was greatly expanded in 2009 thanks to an NIA R01 that funded whole-genome genotyping of nearly the entire cohort with subsequent exome chip genotyping for the entire cohort.
The study has employed a variety of methods to insure timely progression in the planning of the study from its inception. Retention in the study has been excellent with 99% of enrollees accounted for. About 2,100 persons completed the first six of the yearly examinations and 1,400 completed all eight contract-sponsored in-clinic examinations. The mean age of participants in 2011, at the time of the last main examination, was 86 years. Active follow-up of the cohort has now ended.
Significance to Biomedical Research: This clinical research study has been recognized as making a unique contribution to the study of change in body composition and strength in old age and how these changes relate to underlying health conditions and nascent disability. It is one of the few examination studies with large numbers of older African-American participants at baseline. Health ABC has characterized the major weight-related health conditions that might mediate changes in body composition, including diabetes and glucose tolerance, coronary heart disease and stroke, pulmonary disease, osteoporosis, osteoarthritis, and depression. Measures of strength and performance have been followed over the critical decade from age 70-79 and information on physical activity and other health habits has been collected. This study should allow broadening of the perspective on biomedical contributors to independence, function and frailty, major areas of interest at NIA, as well as the interaction of frailty with comorbidity and mortality. This perspective, with increased societal emphasis on health risks of obesity, becomes increasingly important as the proportion of elders grows in the U.S. population.
The study has become a platform for investigators from many institutions beyond the initial field centers and coordinating unit. There are clear guidelines in place for access to the study website and for downloading data for analysis or obtaining DNA or other specimens for further collaboration.