Another aspect of aging slowed by calorie restriction: "Caloric restriction (CR) retards aging in laboratory rodents. [Little] information is available on the effects of long-term CR on physiologic markers of aging and longevity in humans. Heart rate variability (HRV) is a marker for cardiac autonomic functioning. The progressive decline in HRV with aging and the association of higher HRV with better health outcomes are well established. HRV assessment is a reliable tool by which the effects of CR on autonomic function can be assessed. Time and frequency domain analyses compared 24-hr HRV in 22 CR individuals aged 35-82 yrs and 20 age-matched controls eating Western diets (WD). The CR group was significantly leaner than the WD group. Heart rate was significantly lower, and virtually all HRV significantly higher in the CR than in the WD group. HRV in the CR individuals was comparable to published norms for healthy individuals 20 years younger. In addition, when differences in HR and HRV between CR and WD were compared with previously-published changes in HRV induced in healthy adults given atenolol, percent differences in each measure were generally similar in direction and magnitude and suggested declines in sympathetic and increases in parasympathetic modulation of HR and increased circadian variability associated with CR. These findings provide evidence that CR has direct systemic effects that counter the expected age-associated changes in autonomic function so that HRV indexes in CR individuals are similar to those of individuals 20 years younger eating WDs,"