Dr. Bates' Answer: Mature sperm or spermatozoa capable of producing a pregnancy are produced in the male testis approximately every 2.5 months. Therefore, a semen analysis may reflect a man's health many weeks earlier. Sperm number and quality may be reduced by poor health and high body temperature or fever. Elevation of the temperature of the scrotum by sitting in a hot tub may also be detrimental. Type of underwear (briefs vs. boxers) also has the potential to reduce a man's fertility, but the role of boxer shorts in improving sperm quality is controversial at best. In general, loose clothing may keep the testis cooler if prolonged sitting is a part of a man's daily routine. Although health and fitness are important, extreme exercise or cycling may reduce a man's fertility. Finally, the use of steroids, tobacco products or drugs such as marijuana is quite detrimental to a man's fertility, while some vitamins (L-carnitine and anti-oxidants) may enhance sperm parameters.