Here’s yet another reason to wear an activity tracker — exercise may be the key to keeping your body “biologically younger.” During exercise, your muscles secrete a hormone called irisin that can reprogram the body’s fat cells to burn energy instead of storing it. This may help promote weight loss and protect against metabolic diseases like Type 2 diabetes, but there also appears to be a strong anti-aging benefit. Researchers at Ashton’s Research Centre for Healthy Ageing at Ashton University, UK, found a link between irisin levels in the blood and the length of telomeres, small regions at the end of chromosomes that tend to shorten with age. Previous studies have linked shorter telomeres with an increased risk for cancer, heart disease and Alzheimer’s disease. Based on this study of healthy, non-obese people, it appears as if higher levels of irisin are found in people with longer telomeres. In other words, people with higher levels of irisin are “biologically younger” than those with lower levels. Since irisin levels are linked to exercise, it’s not a great leap to suggest that physically active people are more likely to age in a healthier, more youthful body. The study was published in January 2014 AGE.