After the controversial report by Carlsen et al. in 1992 showing a possible decline in human semen quality over the past 50 years, many laboratories investigated their own records of semen findings that had been kept for the past decades, and a significant decrease in sperm quality was reported from some laboratories, but not others. At the beginning of the 21st century, a definitive interpretation of this issue has not yet been offered; however, it seems plausible that there are large regional differences in semen quality. Decreases in semen quality have been reported from various regions around the world, and a concurrent rise in the incidence of other reproductive problems, such as testicular cancer and genital abnormalities, has been observed in many regions. However, most of the reports showing regional differences were from Western or Western-derived countries, despite the fact that Asia is the region with the highest population on earth. Recently we undertook a cross-sectional study on fertile men in Japan to describe the current status of semen quality of Japanese men. We took confounders into consideration to allow a comparison with a previous European study. Japanese fertile men proved to have a semen quality at the level of Danish men, who were reported to have the lowest level among the men examined in the European study. This low level of sperm concentration in fertile Japanese men may result from differences in lifestyle or other environmental factors, but we cannot rule out the possibility of ethnic differences caused by different genetic variation or combination. To address this issue we need more information on the reproductive function in Asian men, who have been reported to have certain differences in reproductive characteristics from Caucasian men. This article is an attempt to review our present knowledge concerning the current status of semen quality in healthy Asian men on the basis of the limited publications from Asia. (Reprod Med Biol 2007; 6: 185-193).
Keywords: Asia; ethnic differences; male reproductive function; semen quality; sperm concentration.