A new study shows that NAD levels are correlated to both your age – and your physical activity. In the study, published in the journal Nature Aging, researchers studied over 50 people: people between 20 and 30 years old, older people aged 65 to 80 with normal levels of physical activity, people 65 to 80 with above-average levels of physical activity, and older people who were physically impaired with very low activity levels. They found that NAD, a metabolite in our bodies that plays a crucial role in mitochondrial energy production, was significantly lower in older patients. But older adults who performed a lot of physical activity on a regular basis had nearly equal levels of NAD compared to the young group. The researchers concluded that most metabolic changes that occur with age in muscle can be reversed with regular exercise training.