L-carnitine, also known as levocarnitine, has been scientifically proven to improve semen quality and production. It is an amino acid that can be found naturally in almonds, dairy products and meat. L-carnitine is an important source of nitruous oxide for the body, which is a chemical compound that relaxes muscles and increases blood flow.
There have been long held beliefs that L-carnitine can improve sperm motility, and these claims are proving true in various medical trials. L-carnitine also has particular benefit to patients with azoospermia. A scientific trial published in Fertility and Sterility in 2003 showed "a statistically significant improvement in semen quality, greater than after the placebo cycle, was seen after the L-carnitine therapy for sperm concentration and total and forward sperm motility."
A later 2005 study published in Drugs in Research & Development also found a "significant correlation between seminal carnitine concentration and sperm concentration, total sperm count, sperm total motility, rapid forward progression, live sperm count, membrane function, nuclear DNA integrity, capacity for cervical mucus penetration, linearity of spermatic movement, and amplitude of lateral sperm head movement", concluding that "L-carnitine may be an effective therapy to improve mainly functional seminal parameters".
A Lenzi, F Lombardo, P Sgro, P Salacone, L Caponecchia, F Dondero and L Gandini (2003). "Use of carnitine therapy in selected cases of male factor infertility: a double-blind crossover trial". Fertility and Sterility, Vol. 79, Issue 2. American Society for Reproductive Medicine via Elsevier.
De Rosa M, Boggia B, Amalfi B, Zarrilli S, Vita A, Colao A and Lombardi G (2005). "Correlation between Seminal Carnitine and Functional Spermatozoal Characteristics in Men with Semen Dysfunction of Various Origins". Drugs in Research & Development, 6(1):1-9. Adis.