Re: Does Size Matter?

[Muckerheide <muckerheide@mediaone.net>]

Hi Martin, group,

The following statement reflects a misperception related to the
effects of radiation:
<snip>
>      I don't think that it matters whether one is discussing external gamma
>      exposure or ingested exposure when considering this, as in both cases
>      the number of DNA breaks will be more-or-less proportional to body
>      mass for a given dose.
<snip> 
The number of DNA breaks is not relevant. Molecular biology that
has been developing since the 1980s has shown that DNA breaks are
more than a 1 million times greater from normal metabolism
(~10^6/cell/day, with 30,000 at any given time, with a repair
half-time of 5 to 45 minutes) vs. background radiation
(~10^-5/cell/day). 

Dozens of normal events (eg, a cup of coffee, exersize, vitamins,
anti-oxidants, etc) overwhelms the oxidative effects of multiples
of background radiation on DNA damage. Although the fraction of
double-strand breaks is greater (2x10^-2 vs 2x10^-5), it is still
insignificant compared to normal metabolism. 

A damaged cell will go through 3 to 6 phases of carcinogenesis,
with up to a billion transformations, before being promoted to a
cancer cell. The known mechanisms of radiation carcinogenesis are
not related to DNA damage, but instead to effects on immune system
and cellular communications functions that control the cellular
and DNA damage prevention, repair, removal processes. 

A synthesis of these results that has been the subject of a review
by leading national experts in the molecular biology of the cell
is being prepared for publication. A June 98 presentation on the
data and analysis with refs can be provided.

Thanks.

Regards, Jim Muckerheide
Radiation, Science, and Health
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