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Re: Debate is over - mistatements of fact
I thought these rather recent abstracts may be of interest since two of them
show interesting inverse associations. To assess the validity of the findings
of these ecologic studies, case-control studies or cohort studies would be
required.
Cancer. 2002 Mar 15;94(6):1867-75.
An estimate of premature cancer mortality in the U.S. due to inadequate doses
of solar ultraviolet-B radiation.
Grant WB.
wbgrant@infi.net
BACKGROUND: There are large geographic gradients in mortality rates for a
number of cancers in the U.S. (e.g., rates are approximately twice as high in
the northeast compared with the southwest). Risk factors such as diet fail to
explain this variation. Previous studies have demonstrated that the geographic
distributions for five types of cancer are related inversely to solar
radiation. The purpose of the current study was to determine how many types of
cancer are affected by solar radiation and how many premature deaths from
cancer occur due to insufficient ultraviolet (UV)-B radiation. METHODS: UV-B
data for July 1992 and cancer mortality rates in the U.S. for between 1970-
1994 were analyzed in an ecologic study. RESULTS: The findings of the current
study confirm previous results that solar UV-B radiation is associated with
reduced risk of cancer of the breast, colon, ovary, and prostate as well as
non-Hodgkin lymphoma. Eight additional malignancies were found to exhibit an
inverse correlation between mortality rates and UV-B radiation: bladder,
esophageal, kidney, lung, pancreatic, rectal, stomach, and corpus uteri. The
annual number of premature deaths from cancer due to lower UV-B exposures was
21,700 (95% confidence interval [95% CI], 20,400-23,400) for white Americans,
1400 (95% CI, 1100-1600) for black Americans, and 500 (95% CI, 400-600) for
Asian Americans and other minorities. CONCLUSIONS: The results of the current
study demonstrate that much of the geographic variation in cancer mortality
rates in the U.S. can be attributed to variations in solar UV-B radiation
exposure. Thus, many lives could be extended through increased careful
exposure to solar UV-B radiation and more safely, vitamin D3 supplementation,
especially in nonsummer months. Copyright 2002 American Cancer Society.
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J Environ Pathol Toxicol Oncol. 2002;21(3):205-12.
Cancer incidence rates and environmental factors: an ecological study.
Steiner GG.
ggsteiner@yahoo.com
The environmental factors latitude, temperature, and water consumption have
been correlatedwithcancerincidencerates.To date, there is noconsensus of
opinion that explains how these environmental factors alter the incidence of
cancer. A fluoride belt stretches across the north and east of Africa, through
the Middle East, across Pakistan and India, into Southeast Asia, and the south
of China. There appears to be an association between areas with low cancer
incidence rates and high fluoride concentrations in the water supply. This
ecologic study attempts to determine if fluoride is correlated with cancer
incidence rates. If so, this study also attempts to determine whether fluoride
is a factor in the correlation between latitude, temperature, and cancer
incidence rates. Population groups with very high cancer incidence rates and
population groups with very low cancer incidence rates are compared to
identify environmental factors that might explain the correlation between
cancer incidence rates and the environmental factors of latitude, temperature,
and fluoride.There is a positive correlation between cancer incidence rates
and latitude (r = 0.71).There is an inverse correlation between cancer
incidence rates and temperature (r = -0.87).There is also an inverse
correlation between cancer incidence rates and fluoride concentration in the
drinking water (r = -0.75). Very low cancer incidence was found in areas with
high fluoride concentrations in the drinking water.
-------------------
Int J Epidemiol. 2001 Dec;30(6):1343-50.
Ecologic versus individual-level sources of bias in ecologic estimates of
contextual health effects.
Greenland S.
Department of Epidemiology, UCLA School of Public Health, and Department of
Statistics, UCLA College of Letters and Science, 22333 Swenson Drive, Topanga,
CA 90290, USA.
A number of authors have attempted to defend ecologic (aggregate) studies by
claiming that the goal of those studies is estimation of ecologic (contextual
or group-level) effects rather than individual-level effects. Critics of these
attempts point out that ecologic effect estimates are inevitably used as
estimates of individual effects, despite disclaimers. A more subtle problem is
that ecologic variation in the distribution of individual effects can bias
ecologic estimates of contextual effects. The conditions leading to this bias
are plausible and perhaps even common in studies of ecosocial factors and
health outcomes because social context is not randomized across typical
analysis units (administrative regions). By definition, ecologic data contain
only marginal observations on the joint distribution of individually defined
confounders and outcomes, and so identify neither contextual nor individual-
level effects. While ecologic studies can still be useful given appropriate
caveats, their problems are better addressed by multilevel study designs,
which obtain and use individual as well as group-level data. Nonetheless, such
studies often share certain special problems with ecologic studies, including
problems due to inappropriate aggregation and problems due to temporal changes
in covariate distributions.
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