If you want to battle the negative biological effects of growing old, you might want to take up an aerobic exercise such as jogging or swimming. German scientists recruited 124 middle-aged men and women who were healthy but didn’t exercise and assigned them workout routines for the next six months. By the end of the study period, those who had been asked to jog or walk briskly for 45 minutes three times a week, or to do a high-intensity interval program, had developed longer telomeres in their white blood cells, reports The New York Times. Telomeres are tiny caps on the ends of chromosomes that protect DNA from damage. These caps shrink as humans get older, eventually resulting in cell death and disease. But aerobic exercise appeared to lengthen the participants’ telomeres, dialing back the aging process. Scientists found no lengthening in the telomeres of participants who took up weight training. The message of the study, says lead author Christian Werner, is that aerobic exercise is good for people of any age. “It is not too late,” he says, “to keep your cells young.”