As men age, their serum concentration of total testosterone decreases only slightly, but because the concentration of sex hormone binding globulin increases, the concentration of free testosterone decreases to a greater degree. The testosterone trials demonstrated that testosterone treatment of elderly men who have low serum testosterone levels increases their sexual function, hemoglobin, and bone mineral density to moderate degrees, and their walking, vitality, and mood slightly. Testosterone treatment increases coronary artery noncalcified plaque volume. However, the trials were not large enough or long enough to know if testosterone treatment increases clinical heart disease or prostate disease.