Sperm count and male fertility: Why are testosterone levels dropping in men?

Sperm count and male fertility: Testosterone is a hormone that affects male physical and mental health. It is produced primarily by the testicles but also by the adrenal glands and testosterone levels naturally decline with age but some studies suggest that they may be declining faster in recent generations. This decline has been linked to a number of factors, including obesity, lack of exercise, stress and exposure to environmental toxins.