Kinetics of human aging: I. Rates of senescence between ages 30 and 70 years in healthy people

A calculation of loss rates is reported for human structural and functional variables from a substantially larger data set than has been previously st udied. Data were collected for healthy, nonsmoking human subjects of both s exes from a literature search of cross-sectional, longitudinal, and cross-s equential studies. The number of studies analyzed was 469, and the total nu mber of subjects was 54,274. A linear model provided a fit of the data, for each variable, that was not significantly different from the best polynomi al fit. Therefore, linear loss rates Cas a percent decline per year from th e reference value at age 30) were calculated for 445 variables from 13 orga n systems, and additionally for 24 variables even more integrative, such as maximum oxygen consumption and exercise performance, that express effects of multiple contributing variables and systems. The frequency distribution of the 13 individual system linear loss rates las percent loss per year) fo r a very healthy population has roughly a unimodal, right-skewed shape, wit h mean 0.65, median 0.5, and variance 0.32. (The actual underlying distribu tion could be a truncated Gaussian, an exponential, Poisson, gamma or some other). The linear estimates of loss rates were clustered between 0% and 2% per year for variables from most organ systems, with exceptions being the endocrine, thermoregulatory, and gastrointestinal systems, for which wider ranges jup to similar to3% per year) of loss rates were found. We suggest t hat this set of Linear losses over time, observed in healthy individuals be tween ages (approximately) 30 to 70 years, exposes the underlying kinetics of human senescence, independent of effects of substantial disease.