The effect of caffeine on the ability of spermatozoa to fertilize mature human oocytes.

Although caffeine has been reported to enhance spermatozoon motility as well as fertilizing ability, its use in clinical practice has remained sparse. We report here the results carried out to assess the effect of exposing normal human spermatozoa to different concentrations of caffeine on their motility, their ability to fertilize oocytes, and the subsequent development of resulting embryos. Mature human oocytes were inseminated with spermatozoa washed and capacitated in 1.25, 2.5, and 5 mM caffeine. The fertilization rates were compared with control oocytes inseminated with untreated spermatozoa. While caffeine was observed to improve significantly various motility parameters in a dose-dependent manner, it did not lead to an improvement in the fertilization rates. At the highest concentration, 5 mM, it adversely affected the fertilization rate: 38%, compared with 78% in controls. Embryonic development was also observed to be retarded at the lower concentrations, while it was virtually inhibited in the 5 mM concentration group. Our results suggest that while a definite improvement in motility may occur when spermatozoa are exposed to caffeine, this improvement did not translate into enhanced fertilizing ability and subsequent embryonic development. We are therefore of the opinion that the use of caffeine as a spermatozoon motility enhancer requires further studies prior to wider clinical use in assisted pregnancy programs.