Muscle loss (sarcopenia)

Research shows that ignoring muscle health is one reason why about 45 percent of older U.S. adults experience muscle loss as they age. "The technical term for this muscle atrophy is sarcopenia, which can begin as early as your 40s and cause unexplained weight loss and reduced strength, energy, and mobility," Sauer says. While hormonal changes can contribute to how your body builds and stores muscle as you age, most cases of sarcopenia are linked to poor nutrition as well as inactivity. One of the best ways to prevent and treat muscle loss, and the weight loss that accompanies it: Add more protein and vitamin D to your diet. "Older adults often require more protein to build the same amount of muscle, since the body becomes less efficient at processing protein," Sauer says.  It's also helpful to add weights to your workouts. "Every time you lift, press, or pull a weight, you create microscopic tears in your muscles—and your body responds with signals to repair your muscles, and then some." The result: You come back to your next workout, as well as everyday tasks, with greater muscle mass and strength.