Activation of Vitamin D in Foods by Ultraviolet Radiation
The quest to trap the sun’s radiant energy in foods to render them antirachitic soon followed.The role of sunlight in rickets was 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