A review of epidemiological studies about the incidence and etiological factors of cryptorchidism--relevance to endocrine-disrupting chemicals

Abstract

Recently, it has been reported that the incidence of male genitourinary abnormalities (such as cryptorchidism) has been increasing because of the presence of endocrine-disrupting chemicals (EDCs) in the environment. This report reviews the papers related to cryptorchidism beginning in the 1960s to clarify the trends in incidence of cryptorchidism and to discuss the association between cryptorchidism and risk factors, including EDCs. The incidence of cryptorchidism tended to increase in almost researched countries until the mid-1980s, but has shown regional differences since 1990. In Japan, the trend of the incidence of cryptorchidism is unclear because there is no monitoring system for cryptorchidism. It is necessary to establish both criteria and a monitoring system to research the incidence of cryptorchidism. The risk factors in epidemiological studies include low birth weight, being small for gestational age, a short gestation period, high maternal body weight, the change during pregnancy of maternal hormones (by exposure to diethylstilbestrol DES or estrogen), and exposure to chemicals. However, the associations between children with cryptorchidism and exposure to EDCs as well as between cryptorchidism and exposure to estrogen of the fetus are not clear because very few reports have quantitatively evaluated EDCs. It is known that some EDCs act as estrogen receptor agonists and change hormonal mobility as exogenous estrogen. It has also been suggested that hormonal drugs such as DES affect the maternal endocrine system in pregnancy and are associated with the incidence of cryptorchidism. In the future, epidemiological studies that clarify the association between cryptorchidism and EDCs such as daidzein and genistein and the quantitative evaluation of exposure factors using biological materials are necessary.