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4. Recommendations on future studies
While organochlorine compounds and other chemical substances
have been shown to affect the endocrine system by in vitro
studies, epidemiologic studies indispensable for evaluation of
actual effects on human health are still scanty. Japanese
subjects have scarcely been studied, while strong concern about
health effects of PCBs and residual organochlorine pesticides in
Europe and America has prompted several large-scale studies,
including nested case-control studies using conserved sera of
cohorts and case-control studies involving biological samples on
breast cancer, which provide important scientific findings.
Verifying the existence of health effects of chemical exposure
specifically on Japanese populations is highly needed, since
they have confounders considerably different from those of
Caucasians, such as exposure level to chemicals, incidence of
diseases possibly related to the exposure, level of endocrine
hormones (including estrogens), use of oral contraceptives or
other hormone preparations, and intake of plant-derived
estrogens (such as those from soybean), as well as genetic
predispositions. The Health and Labor Sciences Research Grants
(Studies on Chemical Risks) have enabled study groups to start
case-control studies on breast cancer, uterine body cancer,
hypospadias, cryptorchidism and endometriosis, a synchronic
study on sperm count, and a synchronic study on populations
occupationally exposed to chemicals at relatively high level.
Although their contributions are expected to be of a certain
value, they will not suffice for any strong evidence of health
effects of chemical exposure because of limitations of
experimental design (limited to case-control and synchronic
studies) and the number of research projects (mostly a single
project for each disease).
We recommend implementation of the following research programs
in order to fill this gap by providing more reliable and
detailed scientific knowledge on human health effects of
chemical exposure.
(1) Investigation of the current situation and monitoring of
exposure level and relevant diseases
Populations representative of the Japanese should be constructed
for determination of chemicals in biological samples. The study
should be continued for regular monitoring of chemical exposure,
for example by expanding the National Nutrition Survey to
include determination of substances which possibly threatens the
national health.
* The U.S. National Center for Health Statistics, controlled by
CDC, included an Environmental Health Profile, consisting of
measurements of residual pesticides, PCBs, dioxins,
phytoestrogens, phthalates and polycyclic aromatic hydrocarbons
in serum or urine, in the National Health and Nutrition
Examination Survey (NHANES) conducted in 1999-2001.
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