USC epidemiologist Ruth K. Peters, Sc.D., professor of preventive medicine, adds that exercise also appears to help prevent the development of type II diabetes. Exercise helps prevent obesity and reduce fat-especially abdominal fat that is associated with heart attacks and type II diabetes. For example, she notes that although the exact mechanism remains unclear, exercise appears to protect people against certain kinds of cancers, most notably cancers of the colon and breast. Studies show that very sedentary people are as much as twice as likely to get such cancers than fervent exercisers. Another striking example is the consistent finding in study after study that exercise has a profoundly positive effect on mood and a person's sense of self-worth, and helps decrease anxiety and depression.
Some studies even show that exercise can significantly reduce the risk of suicide.
S. Victoria Jaque, Ph.D., assistant professor of biokinesiology and physical therapy, says that under normal circumstances, the body continually grows and reabsorbs bone in a fairly stable ratio. Physical stress on the skeletal system seems to alter the ratio slightly so that more bone is formed than reabsorbed. As a result, exercises, especially those that place greater than normal physical loads on the skeletal system, can boost bone density by a small, but significant amount. Humans tend to reach peak bone density in their teens and 20s, then slowly lose bone mass in the decades that follow. Studies show that exercise during and just after puberty can boost an individual's peak bone mass, with potential health benefits for the rest of their lives.