M:F birth ratio update

[ttweed@wildrockies.org (Tony Tweedale)]

Vartianene et al. 'Env Chems & Changes in Sex Ratio: analysis over 250 yrs
in Finland'  _Env Health Perspectives_ 107:10:813-5 ('99)
---

F. has an xclnt birth registry, extremelly stable population and negigible
immigration. that make such a long time curve possible.  It seems really
unusual for such a large number of data points:  the M;F ratio increases in
three steps ie pateaus followed by sudden increases) from 1750 to 1945,
when a decline begins, w/ one step (so far), to the present.

Other countries, esp. in Central Europe, have reported 20th Century
declines in the ratio.  This study argues the decline in male births from
1944 on occured too early to be a respnse from peaks of estrogenic
chemicals in the environment, and presents a fair amnt of data showing when
PCB, PCDD/F and pesticide levels peaked in the Finnish environment and in
its people--they did not precede or coincide w/ the drop in the birth sex
ratio.  Finland stands out for not having had a drop in sperm counts as
many other European countries--env. hormone chemical use generally is
significantly lower than other European countries (tho dose/response issue
is not as important w/ hormonal response, I'd say).  Very high
concentrations of dioxins (eg only the highest exposed at Seveso show a
very significant decrease in male births, but the Taiwan Yucheng PCB/PCDF
poisoning did not significantly affect birth sex ratio.

A bias in the sex ratio of stillbirths could cause a trend in any country's
live birth sex ratio, this study found that it does not account for the
increase portion of its sex ratio time curve.  Historically, chimneny/fire
smoke  and social preference for boys may have altered curves.  Wars
consistently cause an incr. in male births (fascinating)  Any number of
life-style, reprod. and other toxins (cars, smoking,...) and biologic
factors may play a role (e.g. absolute relative age of parents, birth
order, point in menstrual cycle).  This Finish study ruled out hormone
treatments, parental ages, an birth order, though it notes a peak in the
M:F ratio occured when first-borns were dominant in live births (reduced
birth rate, too).

All-in-all, a multi-factorial conundrum with a strange curve.  The Finish
data set of births and env levels of chemicals seems quite reliable, but
with the ability of env. hormones to be active at very low levels, I would
no rule them out from the Finish data, though they are not *evidently* at
work in their running birth sex ratio.


Tony Tweedale

Causality is a concept not subject to empirical demonstration. -David Hume
(1711-'76)

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