Two very simple and inexpensive nutritional supplements sometimes enhance men's fertility, and not only when the man is deficient in the corresponding nutrients. The fertility nutrients are the B-vitamin folic acid and the trace mineral zinc. A clinical trial at University Medical Centre at Nijmegen in the Netherlands found that sperm counts in infertile men increased an average of 74 per cent after taking 6 mg of folic acid and 75 mg of zinc every day for six months. Other research has found that taking 3,000 mg of the amino acid L-carnitine every day for 3 months is helpful when the problem is not sperm count, but rather sperm motility. Taking L-carnitine helps sperm burn glucose to propel themselves through the cervical mucus into the uterus. L-carnitine supplementation will not make every sperm motile, but one test found that the number of motile sperm increased about 50 per cent. One other intervention that can be helpful in the overall plan to increase fertility in men is to wear boxers, not briefs. Loose-fitting underwear allows the testicles to descend away from the body. This keeps them cooler, and allows more sperm to reach maturity and flow into the prostate to be combined with semen.