This hormone contributes to energy, muscle mass, strength, endurance, decreased fat, increased exercise tolerance, enhancement of well-being, and psychological status. Testosterone protects against cardiovascular disease, hypertension, obesity, and arthritis. It leads to improved lean muscle mass, increased libido, and sexual performance. The majority of testosterone is produced in the male testes and in the female ovaries but both sexes produce the hormone in the adrenal glands as well. Testosterone levels can dramatically decline after the age of forty in both men and women. A common symptom of declining testosterone in the male (Testosterone deficiency syndrome) is fatigue. A common symptom of low testosterone in females may be low libido. Testosterone is extremely important in the male as well as the female.