Illegal drug use. Anabolic steroids taken to stimulate muscle strength and growth can cause the testicles to shrink and sperm production to decrease. Use of cocaine or marijuana may temporarily reduce the number and quality of your sperm as well.
Alcohol use. Drinking alcohol can lower testosterone levels, cause erectile dysfunction and decrease sperm production. Liver disease caused by excessive drinking also may lead to fertility problems.
Occupation. Certain occupations can increase your risk of infertility, including those associated with extended use of computers or video display monitors, shift work, and work-related stress.
Tobacco smoking. Men who smoke may have a lower sperm count than do those who don’t smoke. Secondhand smoke also may affect male fertility.
Emotional stress.Stress can interfere with certain hormones needed to produce sperm. Severe or prolonged emotional stress, including problems with fertility, can affect your sperm count.
Weight. Obesity can cause hormone changes that reduce male fertility.
Prolonged bicycling. Prolonged bicycling is another possible cause of reduced fertility due to overheating the testicles. In some cases, bicycle seat pressure on the area behind the testicles (perineum) can cause numbness in the penis and erectile dysfunction.