Another reason to exercise: "Senescent T-cells accumulate with age, lowering the naive T-cell repertoire and increasing host infection risk. As this response is likely to be influenced by certain lifestyle factors, we examined the association between aerobic fitness (VO(2max)) and the age-related accumulation of senescent T-cells. Blood lymphocytes from 102 healthy males (18-61yr) were analyzed for [marker] surface expression on CD4+ and CD8+ T-cells ... Advancing age (yr) was positively associated with the proportion (%) of senescent [and] CD8+ T-cells and inversely associated with naive CD4+ and CD8+ T-cells. VO(2max) was inversely associated with senescent CD4+ and CD8+. Strikingly, age was no longer associated with the proportions of senescent or naive T-cells after adjusting for VO(2max), while the association between VO(2max) and these T-cell subsets withstood adjustment for age, BMI and percentage body fat. Ranking participants by age-adjusted VO(2max) revealed that the highest tertile had had 17% more naive CD8+ T-cells and 57% and 37% less senescent CD4+ and CD8+ T-cells, respectively, compared to the lowest tertile. This is the first study to show that aerobic fitness is associated with a lower age-related accumulation of senescent T-cells, highlighting the beneficial effects of maintaining a physically active lifestyle on the aging immune system."