everyone's testosterone lowered by environmental endocrine disruptors:
Travison, Araujo, OÕDonnell, Kupelian, McKinlay.
A population-level decline in serum testosterone levels
in American men. J Clinical Endocrinology and Metabolism 2007.
( Study Observation years Age range (yr)
, TotalTestosterone (ng/dl) (Median, Interquartile range)
, Bioavailable T (ng/dl) (Median, Interquartile range)
1987– 89 age45–71
(501, 392– 614); (237, 179 –294)
1995–97 age50 – 80
(435, 350 –537); (188, 150 –234)
2002– 04 age57– 80
(391, 310 –507), (130, 101–163)
. weight gain, smoking cessation, and the use of medications
have been associated with decreases in serum T (33–37);
however this does not explain how
the past 20 yr have seen substantial age-independent
decreases in male serum T concentrations:
these decreases that do not appear to be the consequence
of the contemporaneous trends in health and lifestyle considered here.
It remains unclear to what these apparent population-level
decreases in T are attributable.
Recent studies have found
environmental impacts on testosterone levels.
testosterone levels were lower in US Air Force veterans
exposed to dioxins while spraying Agent Orange
as well as in men exposed to phthalates at work.
The results are surprisingly consistent with another set of
long-term human epidemiology studies
showing a long-term decline in male reproductive functions,
such as decreased sperm health and increased infertility,
which are highly associated with or controlled by
testosterone and other androgen hormones.
The rate of decline reported in this study
is roughly comparable to the rate of decline of sperm count
reported first by:
Carlsen, E., A Giwercman, N Keiding, N Skakkebæk. 1992.
Evidence for Decreasing Quality of Semen During Past 50 Years.
British Medical Journal 305:609-613.
. see other evidence of endocrine disrupting pollution.
testing has assumed dose makes the poison:
Regulatory toxicology has assumed that
high dose experiments can be used to
predict low-dose results.
A substantial body of scientific evidence published in
the peer-reviewed literature
challenges the central tenet of regulatory toxicology,
which assumes 'the dose makes the poison.'
Experimental data now conclusively show that
some endocrine-disrupting contaminants
can cause adverse effects at low levels
when there are no effects at higer doses.
How toxicology tests are used to develop health standards:
To set exposure limits, three to five doses of a substance
are tested in the laboratory. Toxicologist start at the
highest dose chosen and continue to lower doses
until they find the point where effects are no longer detectable,
that is, the dose at which experimental animals
no longer differ from controls. This safe dose
- the lowest amount that poses an acceptable risk -
is called the 'no observed adverse effect level,' or NOAEL.
Traditional toxicology guiding health regulations
rarely tests doses lower than NOAEL
due to the 'dose makes the poison' assumption.
The final acceptable level for human exposure
is set to be a small fraction of the NOAEL
but this ignores that the unfortunate fact that
many chemical endocrine disruptions
happen only at very small doses.