Dioxin Exposure and Cardiovascular Disease
An Analysis of Association
Dioxins have long been known as highly toxic compounds, having been
implicated in cancer, immune system disorders, endocrine disruption,
and birth defects. Animal and
in vitro
studies have also suggested a role for dioxins in heart disease. Now a
systematic review of epidemiologic studies has found an association
between dioxin exposure and death from cardiovascular diseases,
particularly ischemic heart disease (reduced blood supply to the heart)
The authors reviewed all English-language
studies on dioxin exposure and death from cardiovascular disease
reported in PubMed as of December 2007. They used a broad definition of
"dioxins" that included polychlorinated dibenzofurans (PCDFs),
polychlorinated biphenyls (PCBs) with dioxin-like effects, and
polychlorinated dibenzo-
p-dioxins
(PCDDs). However, they excluded studies that focused primarily on PCBs
because results pertaining to the non–dioxin-like members of this
family would muddy the interpretation of dioxins' cardiovascular
effects. Likewise, studies of occupational exposure in the leather
processing and flavor/fragrance industries were excluded because
workers in these industries are exposed to cardiotoxic methylmercury,
arsenic, and xylene along with dioxin.
The remaining studies included 12 dioxin-exposed
cohorts, one of which was a large multicenter cohort study; 10 of these
cohorts involved military or occupational dioxin exposure, and 2
involved environmental exposure of the general public. The cohorts
included Vietnam veterans exposed to herbicides; the population of
Seveso, Italy, exposed in 1976 by an industrial accident to
2,3,7,8-tetrachlorodibenzo-
p-dioxin (TCDD), the most toxic dioxin; and a Taiwanese population exposed in 1979 to polychlorinated dibenzofurans in rice oil.
The researchers identified numerous potential limitations in the
reviewed studies. For example, none of the studies adjusted for all the
known cardiovascular risk factors of diet, smoking, physical activity,
family history, and body mass index, so residual confounding was a
concern. Furthermore, not all studies made internal comparisons between
lowest-exposed and highest-exposed members of a cohort. Some compared
the exposed cohorts with the general population, which may confound
results because of the "healthy worker effect" (that is, workers as a
group are typically healthier than the general population, which
includes those who are too ill to work). There was also wide variation
in the precision of exposure estimates.
Despite these potential limitations, the authors
concluded that the literature as a whole presented reasonable evidence
that dioxin exposure at high doses raises the risk of death from heart
disease. They suggest the need for further studies that account for the
limitations in the existing studies, particularly with respect to
confounders, choice of comparison populations, and environmentally
relevant exposure concentrations.
from ehponline.org
