Does switching from briefs to boxers give guys' sperm extra oomph? Probably not - at least not enough to worth bothering with, says sperm expert Dr. Craig Niederberger, professor of urology at the University of Illinois and prospective editor-in-chief of the journal Fertility and Sterility. But there are many things - including some unexpected ones - that do take a toll on sperm and compromise male fertility.
Keep clicking as Dr. Niederberger explains what every guy should know about 11 sperm-killers...
Nicotine slows sperm cells' swimming speed and damages their precious cargo, the DNA that ultimately combines with eggs' to make embryos. Worse yet, nicotine blocks blood flow to the penis and damages the spongy tissue inside that expands to cause an erection.
Want your sperm (and penis) to work? Don't smoke.
Doctors continue to debate the health effects of bisphenol A, a compound found in all sorts of consumer items, from some plastic bottles to cash-register receipts. One thing it seems to do is act like estrogen in the body. If enough of the stuff finds its way into a guy's blood, sperm are likely to decline in number and in their all-important swimming ability.
In small amounts, alcohol is fine for sperm. But if a guy drinks enough to poison his liver, his sperm production will also suffer. With alcohol as with many things in life, moderation is best. Many doctors say two drinks a day is the upper limit.
Lubricants used during sex can slow sperm down and even degrade its DNA. That goes for saliva as well as store-bought lubricants. Recent research suggests that a lubricant known as PreSeed is less likely to ruin sperm.
Abusing testosterone and other anabolic steroids can trick the testicles into thinking that they don't need to make testosterone. As a result, sperm production falls, and the testicles shrink. Testosterone has even been studied as a male contraceptive.
Some plants foods are rich in estrogen-like compounds called phytoestrogens. Soy, in particular, contains lots of the stuff. Consumed later in life, soy can help protect guys against prostate cancer. But young men eager to maximize their fertility might want to limit their soy intake.
To make sperm, the body needs a steady flow of nutritious food - especially protein, folate-rich leafy green vegetables, and brightly colored vegetables with antioxidants. Pizza and beer alone won't do.
Cadmium, a metal found in batteries and paint pigments, is a sperm assassin. Be careful if you work around batteries or yellow paint.
Pot turns men's hormones inside out, lowering testosterone levels and raising levels of the female hormone estrogen. Sperm cells need testosterone to grow.
Long-term use of narcotics can compromise the body's ability to make testosterone. Less testosterone means fewer sperm.
Keeping the weight off might not be the only reason a guy would want to cut back on fatty foods. Dioxin, a toxin found in animal and plant fats, lowers sperm counts and interferes with sperm cells' swimming ability.