"Middle age is defined as the period from age thirty-one to fifty. The early period of this stage is very different from the end. For example, during the early years of middle age, many women experience pregnancy, childbirth, and lactation. In the latter part of this life stage, women face perimenopause, which is a transition period that leads up to menopause, or the end of menstruation. A number of physical changes take place in the middle-aged years, including the loss of bone mass in women due to dropping levels of estrogen during menopause. In both men and women, visual acuity declines, and by age forty there can be a decreased ability to see objects at a close distance, a condition known as presbyopia. All of these are signs of aging, as the human body begins to change in subtle and not-so-subtle ways. However, a middle-aged person can remain vital, healthy, and near his or her physical peak with proper diet and adequate exercise. During this stage of the human life cycle, adults begin to experience the first outward signs of aging. Wrinkles begin to appear, joints ache after a highly active day, and body fat accumulates. There is also a loss of muscle tone and elasticity in the connective tissue. Many people in their late thirties and in their forties notice a decline in endurance, the onset of wear-and-tear injuries, such as osteoarthritis, and changes in the digestive system. Wounds and other injuries also take longer to heal. Body composition changes due to fat deposits in the trunk. To maintain health and wellness during the middle-aged years and beyond, it is important to maintain a healthy body weight, consume nutrient-dense foods, drink alcohol moderately or not at all, be a nonsmoker, and engage in moderate physical activity at least 150 minutes per week."