In the general sense, anything that promoted cancer would obviously be
"toxic."  In a clinical nutrition sense, a megadose of a vitamin considered
a toxic dose has a more immediate sense of "poisoning."  In fact, the NAS UL
are based on this second sense.  To make an extreme example, there is a
certain supplement which has the unfortunate tendency to swell in the throat
and has caused deaths; the supplement is not considered to be toxic at the
levels at which these deaths have occurred, because it kills by mechanical
means rather than by direct poisoning.  

However, in the case of the cancer study, Lara makes a good argument that it
should be considered a type of toxicity, and she is probably right.  It
lacks the immediacy of the acute toxicity experienced by adventurers who
died from hypervitaminosis-A after consuming polar bear liver, but it may be
toxicity after all.  We are lacking information on the mechanism by which
the cancers were stimulated, although the results are clear enough to
support Lara's point.  

The National Academy of Sciences states that "most nutrients are not
considered to be carcinogenic in humans," but this may turn out to be one of
the exceptions, once other possible variables have been excluded.  As an
example of a confounding variable in supplement risk assessment, several
years ago tryptophan supplements were taken off the market, not because of
any intrinsic problem with tryptophan (although this first appeared to be
the case), but because of an impurity in the product caused by a certain
manufacturing process. 

Lactnetters are an incredibly rich resource. As different Lactnetters
present information they know best--from public health, nursing, medicine,
nutrition, psychology, and so on--we can adjust and fit these bits of
knowledge into a more comprehensive whole.  What makes our information more
trustworthy than that which is offered by society at large is our careful
attention to the facts, and our exactitude in differentiating what we know
from what we don't know. We know that hypervitaminosis-A is
toxic--immediately and dangerously so.  Lara makes a good case for stating
that hypervitaminosis-carotene may also be toxic, athough not so immediate.

I am happy to have my mind changed by those who present a good scientific
case for their argument, as Lara has done.

Arly Helm, MS, IBCLC 

             ***********************************************

To temporarily stop your subscription: set lactnet nomail
To start it again: set lactnet mail (or digest)
To unsubscribe: unsubscribe lactnet
All commands go to [log in to unmask]

The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(R)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html