Holistic-medicine devotees have been talking for decades about how chronic inflammation ages the body, but concrete proof of that has been elusive. Now, however, the longest-running human-aging study, the BLSA, has inched closer to proof. The BLSA has shown that having more than one disease, which doctors call "comorbidity," is a good indicator of how rapidly a person is aging, and it seems to be driven by chronic inflammation. That happens when the immune system's natural reaction to insult gets stuck in the "on" position. "Chronic inflammation seems to be the strongest predictor of comorbidity," says Dr. Luigi Ferrucci, scientific director of the National Institute on Aging and former director of the BLSA. The researchers aren't sure yet if that inflammation is a primary cause of aging, "but certainly it's an accelerator," Ferrucci says. Habits that have been linked to lower inflammation include a diet rich in plants and omega-3 fatty acids, mindfulness meditation and regular exercise.