Accumulation of health disorders as a systemic measure of aging: Findings from the NLTCS data.

Background: An index of age-associated health/well-being disorders (deficits), called the "frailty index" (FI), appears to be a promising characteristic to capture dynamic variability in aging manifestations among age-peers. In this study we provide further support toward this view focusing on the analysis of the FI age patterns in the participants of the National Long Term Care Survey (NLTCS).

Methods: The NLTCS assessed health and functioning of the U.S. elderly in 1982, 1984, 1989, 1994, and 1999. Detailed information for our sample was assessed from about 26,700 interviews. The individual FI is defined as a proportion of health deficits for a given person.

Results: The FI in the NLTCS exhibits accelerated age patterns. The acceleration is larger for elderly who, at younger ages, had a lower FI (low FI group) than for those who showed a higher FI at younger ages (high FI group). Age-patterns for low and high FI groups tend to converge at advanced ages. The rate of deficit accumulation is sex-sensitive.

Conclusions: The accelerated FI age patterns suggest that FI can be considered as a systemic measure of aging process. Convergence of the (sex-specific) FI age patterns for low and high FI groups by extreme ages might reflect the limit of the FI-specific (or systemic) age as well as the limit of adaptation capacity in aging individuals.