You run for 40 minutes a day

Scientists in California found that middle-aged people who did just that—for a total of about 5 hours per week—lived longer and functioned better physically and cognitively as they got older; the researchers tracked runners and nonrunners for 21 years. "What surprised us is that the runners didn't just get less heart disease—they also developed fewer cases of cancer, neurologic diseases, and infections," says study author Eliza Chakravarty, MD, an assistant professor of medicine at Stanford University School of Medicine. "Aerobic exercise keeps the immune system young." If you don't like to run, even 20 minutes a day of any activity that leaves you breathless can boost your health, she says.