Activation of Vitamin D in
F
oods by Ultraviolet Radiation
The quest to trap the sun’s ra-
diant energy in foods to render
them antirachitic soon followed.
The role of sunlight in rickets
wa
s shrouded in mystery.
75
It
w
as evident that direct ultraviolet
irradiation could promote growth
in rats maintained on a vitamin
D–deficient diet containing a
high calcium and low phospho-
rus content. Ultraviolet irradia-
tion from mercury vapor lamps
promoted growth in rats failing
to thrive on diets deficient in fat-
soluble vitamin A, despite the
r
ats’ overt vitamin A deficiency
(progressive xerophthalmia).
76
Heated and oxidized cod liver oil
(devoid of vitamin A) was com-
parable to ultraviolet irradiation
in growth promotion, suggesting
that the antirachitic agent in ul-
traviolet radiation and cod liver
oil were identical in function.
76
In 1923, Eleanor Hume and
Hannah Smith reported from
England that rats transferred to
“
empty” jars that were previously
exposed to ultraviolet radiation
grew as well as rats that were irra-
diated directly; they concluded
that “irradiated air” was imparted
with a growth-promoting prop-
erty.
77
Attempts to corroborate
their study, however, were unsuc-
cessful.
78,79
E. M. Nelson and
Harry Steenbock of the University
of Wisconsin at Madison were
aware of Hume and Smith’s re-
port and speculated that the pro-
tection noted in the “empty” irra-
diated jars was perhaps because
of the activation of residual saw-
dust or foods that were not re-
moved prior to the irradiation of
the jars.
79
They were intrigued by
the results of their own irradiation
experiments. Much to their
amazement, rats maintained on a
r
achitogenic diet began to grow
when irradiated rats were intro-
duced into their cage.
79
They at-
tributed the growth promotion in
the nonirradiated rats to the in-
gestion of the “photochemically