8
The Vitamins
David A Bender
Key messages- The vitamins are a chemically disparate group of compounds with
a variety of functions in the body. - What they have in common is that they are organic compounds
that are required for the maintenance of normal health and meta-
bolic integrity. - Vitamins are required in very small amounts, of the order of mil-
ligrams or micrograms per day, and thus can be distinguished
from the essential fatty acids and the essential amino acids,
which are required in larger amounts of grams per day.
© 2009 DA Bender.
- Where relevant, this chapter will deal with each of the vitamins
under the following headings:- vitamers
- absorption and metabolism
- metabolic functions and other uses
- defi ciency
- requirements
- assessment of status
- toxicity and drug interactions.
8.1 Introduction
In order to demonstrate that a compound is a vitamin,
it is necessary to demonstrate both that deprivation
of experimental subjects will lead to the development
of a more or less specifi c clinical defi ciency disease
and abnormal metabolic signs, and that restoration
of the missing compound will prevent or cure the
defi ciency disease and normalize metabolic abnor-
malities. It is not enough simply to demonstrate that
a compound has a function in the body, since it may
normally be synthesized in adequate amounts to meet
requirements, or that a compound cures a disease,
since this may simply refl ect a pharmacological action
and not indicate that the compound is a dietary
essential.
The vitamins, and their principal functions and
defi ciency signs, are shown in Table 8.1; the curious
nomenclature is a consequence of the way in which
they were discovered at the beginning of the twentieth
century. Early studies showed that there was some-
thing in milk that was essential, in very small amounts,
for the growth of animals fed on a diet consisting of
purifi ed fat, carbohydrate, protein, and mineral salts.
Two factors were found to be essential: one was found
in the cream and the other in the watery part of milk.
Logically, they were called factor A (fat-soluble, in the
cream) and factor B (water-soluble, in the watery part
of the milk). Factor B was identifi ed chemically as an
amine, and in 1913 the name “vitamin” was coined
for these “vital amines.”
Further studies showed that “vitamin B” was a
mixture of a number of compounds, with different
actions in the body, and so they were given numbers as
well: vitamin B 1 , vitamin B 2 , and so on. There are gaps
in the numerical order of the B vitamins. When what
might have been called vitamin B 3 was discovered, it
was found to be a chemical compound that was already
known, nicotinic acid. It was therefore not given a
number. Other gaps are because compounds that were
assumed to be vitamins and were given numbers, such
as B 4 and B 5 , were later shown either not to be vitamins,
or to be vitamins that had already been described by
other workers and given other names.
Vitamins C, D and E were named in the order of
their discovery. The name “vitamin F” was used at one
time for what we now call the essential fatty acids;
“vitamin G” was later found to be what was already