Temporal changes in the last 50 years of testis-weight indicate subtle male reproductive disorders in Japan

The ever increasing presence of environmental toxicants and their disrupting effects on the reproductive systems of wildlife, raise the question of their possible damaging effects on the human reproductive system. Using medicolegal data from over 20,000 Japanese men subjected to necropsy from 1948 to 1998, we investigated temporal changes of testis-weight to find possible evidence of male reproductive disorders. We also made histological observations of 747 testes collected from 1978 to 1998. Our detailed analyses indicates that the development of testis-weight over the last fifty years has followed four marked phenomena: (a) the age at which testis-weight reaches its maximum has become younger, (b) the weight at peak had become generally higher, until a decline in peak-weight beginning after 1960 birth years, (c) the decline-rate at which testis-weight decreases after its peak has greatly accelerated, and (d) the onset of testis-weight of boys has started progressively younger. Our quantitative analyses of testis-weight indicate some possibility of a subtle reproductive disorder in Japanese men, especially those born after 1960. Together with the accelerated development and decline of testis-weight during the last fifty years, the decline in peak-weight might be indicative of a subtle interference of environmental toxicants with male reproductive organogenesis.