Epidemiologic evidence of environmental endocrine disruption is harder to come by in part due to the usual ethical constraints. Also, evidence of this type cannot demonstrate endocrine disruption directly as the mechanism inducing the effects. Yet in spite of such limitations, intriguing observations from epidemiology studies continue to emerge at a steady pace.

Two studies had linked atrazine to ovarian tumors in women (Donna et al., 1984, 1989). This antiandrogenic herbicide is known to be capable of affecting ovarian function (Cooper et al., 1996) and steroid metabolism (Babic-Gojmerac et al., 1989; Crain et al., 1997; Hayes et al., 2002) in animals. Such animal data offer further support for the above epidemiologic link.

A more recent study by Vreugdenhil et al. (2002) reported that perinatal exposure to PCBs is associated with changes in play behavior of children. This epidemiology study also showed more feminized behaviors in both boys and girls exposed prenatally to higher levels of dioxins. Although this is perhaps the first study ever reported linking disruption effects of this type to child behavior, its results are consistent with findings observed in animal studies.

The link between light at night and an increased risk of breast cancer was provided in two independent epidemiology studies in the same year (Davis et al., 2001; Schernhammer et al., 2001). It was explained that, through photic information from the retina, visible light would suppress the normal nocturnal production of melatonin by the pineal gland (Hansen, 2001). The two epidemiology studies thus support the earlier in vitro work by Blask et al. (1997), that the pineal hormone has the potential to restrain tumor growth, especially in breast cells.