Examination of Witness (Questions 200 - 219)
TUESDAY 19 MAY 1998
PROFESSOR H F WOODS
200. So if the Dalton and Dalton study is discredited, and
we will come to that in a few minutes with other questioners,
does the essential basis of your recommendation collapse?
(Professor Woods) No, because we do not agree with
you that the Dalton and Dalton study is discredited, as you say.
201. So the American Academy of Sciences is wrong?
(Professor Woods) We do not agree with the interpretation,
we do not completely agree with the interpretation of the NAS
report in relation to vitamin B6.
202. But it says that Dalton and Dalton is unreliable, does
it not?
(Professor Woods) That is their opinion, Mr Mitchell.
That is not our opinion.
203. So there is other evidence besides Dalton and Dalton
that intakes of over 100 mg have toxic consequences?
(Professor Woods) Yes.
204. Is that just the animal evidence or is there other human
evidence?
(Professor Woods) No, I am talking about the animal
evidence here.
205. Just the animal evidence supporting Dalton and Dalton?
(Professor Woods) Yes.
Mr Marsden
206. What we are seeing here is that the Phillips et al
study was supporting Dalton and hence helped you to come to your
recommendations that you needed actually to recommend the introduction
of a lower limit, so, therefore, what is your response where in
the report of Phillips et al it says, "With the information
presently available, it would be premature to extrapolate to other
species, including man" and that is with regards to the toxicological
evaluation of pyridoxine HCL.
(Professor Woods) Yes.
207. What is your response?
(Professor Woods) I wonder if you would allow me,
Mr Marsden, to say something about the way in which the Committee
on Toxicity works because I think that this is fundamental to
answering your point. The fundamental processes that are involved
in formulating advice of this nature are to identify from the
original literature, and that is both animal and human data, so
we would use that data, the lowest observed effect level or a
no observed effect level, if that were possible to identify, and
to apply safety or uncertainty factors to those dose levels in
order to arrive at a daily dose for man. That is standard technique.
It is standard technique in this country, it is standard technique
on the Continent of Europe, and it is used by those committees
that have a function that is comparable to or parallel with the
Committee on Toxicity. It is a standard practice to use data of
that nature, to apply safety or uncertainty factors to it and
to then arrive through animal data at a figure that we would,
for example, for an additive apply as being or describe as being
an acceptable daily intake. That is a standard procedure.
208. But, with due respect, with Phillips, when you extrapolate
the equivalent of 3,000 mg per day for a human—
(Professor Woods) Yes, but that is—
209. It does not stack up. The previous witnesses have made
it quite clear that over 500 mg a day could prove to be dangerous,
so that study simply reinforces that, so how can you, therefore,
extrapolate and say you are putting in a 300-fold safety factor
and get it down to 10?
(Professor Woods) Because the safety factors that
are applied by the Committee on Toxicity and comparable—
210. So the 300 is standard, is it?
(Professor Woods) The safety factors that are applied
by the Committee on Toxicity and comparable committees have to
take into consideration two matters. One is the extrapolation
from one species to another, in other words, from dog to man,
and also to take into consideration the variability within human
populations because, as you know, the response in a human population
is not identical person to person, and that is how we arrive at
a substantial safety factor which would bring that figure down.
211. So you looked at evidence and I am assuming you looked
at evidence which said 10 mg per day is safe, and that was proven?
(Professor Woods) No, we arrived at—
212. Exactly, that is my point. You are then making a judgment
saying that 10 mg may be safe based on extrapolation, but the
only evidence that we seem to be able to come across to say 50
plus is dangerous and then you actually start looking at, for
instance, respected institutions across the water, they actually
then err on the side of caution and go up to 100 mg, but no one
can seem to get it below that purely other than plucking figures
out of the air, and I put it to you that that is what you seem
to have done because you cannot give evidence to us suggesting
that plus 50 mg per day is actually dangerous.
(Professor Woods) We believe that the proper application
of the facts in Dalton and Dalton—
213. Where is the proof? You have given a submission, with
all due respect, to the House of Commons Select Committee on Agriculture
and in there all you refer to is Dalton and then you refer to
Phillips. Where is your evidence that suggests that more than
50 mg per day of vitamin B6 is dangerous?
(Professor Woods) We based that on the Dalton and
Dalton study mainly.
Chairman: I think it would be helpful, if that is the case,
I do not like to change the order of questioning but in view of
what you have just said I think we ought to move on to the Dalton
and Dalton study in some detail.
Mr Mitchell
214. Can I just ask this, because the Chairman did remind
me that in my eagerness to develop my skills as a barrister in
case I did not make it in politics I omitted the central question
which was why were the data on human toxicity adequate by themselves
in 1995, but no longer in 1997?
(Professor Woods) I did not say they were no longer
in 1997.
215. That is what your report said.
(Professor Woods) What I am saying now, and I am not
quite sure which document you are referring to, is that the main
paper upon which we based our calculation was the Dalton and Dalton
paper but in keeping with our normal practice and in relation
to the way we look at other chemical compounds we are interested
to see whether or not animal studies do give any supporting indication.
216. You had those in 1995, of course.
(Professor Woods) I would point out to you that, of
course, one of the main interests of the animal studies relates
to shedding light upon the mechanisms because there was substantial
histological analysis in those dog studies.
217. Okay. Since your recommendations were made you must
have had a lot of correspondence, as we all have, arising from
your decision. A lot of it would be denouncing the decision. Have
you had any indications of toxic damage to anyone, any evidence
about toxic damage, which has come to you since you made that
recommendation from taking over 10 mg of B6 a day?
(Professor Woods) As an individual or as a committee?
218. As a committee. Or do you know of any through the professional
literature? The answer is no, is it not?
(Professor Woods) I am about to give you an answer,
Mr Mitchell, if you just give me a moment or two. The answer is
that certainly so far as the use of vitamin B6 under the terms
of the Food Safety Act is concerned, namely as a food, to my knowledge
or to the committee's knowledge, there is no system set up which
is a surveillance system which would allow that data to emerge.
The only data on adverse effects of vitamin B6 taken by man for
medicinal purposes is that which is collected through the Committee
on the Safety of Medicines.
Chairman: I think Mr Mitchell has given us a bridge back
to our original order of questions. I would like to ask Mrs Organ
to continue.
Mrs Organ
219. You say no other data. Obviously the European Union
Scientific Committee on Food made a recommendation that intakes
of more than 50 mg of vitamin B6 per day must be regarded as potentially
harmful. I wonder if you can give us a little explanation as to
the context of their statement on that? Was this arrived at as
a result of a full review of scientific evidence that they had
taken on board of the toxicity of vitamin B6 and on what grounds
were they able to make this statement?
(Professor Woods) Unfortunately, Mrs Organ, I do not
have access to the papers of the SCF and I am not aware of the
content of the data which they surveyed or considered in their
committee in order to reach that decision. I know that the Scientific
Committee on Food in Europe does contain toxicologists in its
membership.
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