In athletes, the rarely identified malady of osteoporosis differs from other chronic effects of exercise. The most obvious difference is that hormonal imbalance leads to compensatory mechanisms that in turn lead to osteoporosis and increased incidence of fracture. Most research on this subject has dealt with women, because hormonal imbalances in women are easier to detect than those in men. Endurance athletes are known to have decreased levels of sex hormones, which can cause physiologic changes that lead to bone loss. This may result in relative osteoporosis despite the loading of the bone during exercise, which would normally increase bone mineral density. Premature osteoporosis may be irreversible, causing young athletes to become osteoporotic at an earlier age and have an increased risk of fracture later in life.