Vitamin D can be synthesized endogenously in the skin with exposure to ultraviolet (UV) light. Together, vitamin D and calcium help build and maintain growing bone. Exercise helps build bone mass, which protects against osteoporosis later in life, particularly in women. Renal function is not greatly affected by the environment. There are some deleterious effects on the eye (cataracts) and the skin (cancer, elastosis) from increased exposure to UV radiation in sunlight. Increased air pollution in many cities has led to an increased incidence of pulmonary diseases, and children are particularly at risk.