Nutrient Supplementation

Improving Male Fertility Fourfold

Cesar Mora-Esteves, MD; David Shin, MD


Semin Reprod Med. 2013;31(4):293-300. 

In This Article


Carnitine is a water-soluble antioxidant mostly derived from human diet. Extracellular and intracellular carnitine may play a role in sperm energy metabolism, providing the primary fuel for sperm motility. Spermatozoa show increased l-carnitine and l-acetylcarnitine concentrations during epididymal passage and acquisition of motility.[23]

Carnitines accumulate in the epididymis in both free and acetylated forms and are used by spermatozoa for mitochondrial b-oxidation of long chain fatty acids, since this is the principal shuttle and transfer system of the acyl to the mitochondrial CoA.[24,25] They enhance the cellular energetics in mitochondria by facilitating the entry and utilization of free fatty acids within the mitochondria and also restore the phospholipid composition of mitochondrial membranes by decreasing fatty acid oxidation.[26–28] Carnitine protects sperm DNA and cell membranes from free radical-induced damage and apoptosis[27,29–31] and has been correlated with sperm parameters such as concentration and motility, which relate to higher fecundity.[32,33] It is believed that initiation of sperm motility occurs in parallel to an increase in carnitine concentration in the epididymal lumen and l-acetylcarnitine in spermatozoa.[34,35] Acetylation of carnitine was found to be greater in motile than in immotile spermatozoa.[36] Patients with defective sperm motion parameters were shown to have reduced l-acetylcarnitine/l-carnitine ratio.[37]

Preliminary, uncontrolled studies suggest that oral carnitine supplementation has a favorable effect on sperm motion characteristics of infertile men.[38–40] A dose of 3 g of carnitine daily for 3 or 4 months[38,39] significantly improves a patient's sperm motility, compared with pretreatment levels. A daily dose of 4 g over 2 months improved motility in 15 of 20 patients. This effect was more evident in seven patients whose partners achieved pregnancy during treatment and follow-up. The utility of carnitine to improve sperm motility is supported by more recent, randomized, controlled trials in which 2 g carnitine was administered daily.[27,29,30] The most significant improvement was seen in the groups with lower baseline motility.[27,29] However, studies by Lenzi et al failed to demonstrate any improvement in morphology, suggesting that carnitine's effects are posttesticular.[27,29] On the contrary, Cavallini et al reported improved morphology at 3 and 6 months in the course of therapy.[30] In both of these studies, there was no further improvement seen in other semen parameters at 3 and 6 months of carnitine therapy.