Newsletter 02 2006.pdf - Sight and Life

NEWSLETTER 2/2006
11
SIGHT AND LIFE
EV McCollum Paul Karrer Otto Isler (left)
function of vitamin A outside the
visual cycle was still speculative
(11). Analytical methods for quantitative
analysis existed for both
the preformed vitamin and for
provitamin carotenoids, but these
methods were often tedious, difficult
to standardize, and frequently
used toxic chemicals that failed
to provide reproducible results in
many laboratories (12–14). There
were no large-scale intervention
programs to combat vitamin A
deficiency and even at the local
level within hospitals there was
little appreciation of how to treat
or prevent the deficiency, which
often accompanied proteinenergy
malnutrition (PEM). And
notably, there was very little political
interest or will to eliminate
vitamin A deficiency.
I saw my first cases of xerophthalmia
in 1961, more than four
decades ago, while conducting
doctoral research among refugee
children in what was then Jerusalem,
Jordan. I was midway
through studies at Columbia
University Institute of Nutrition
Sciences, later renamed the Institute
of Human Nutrition (IHN).
I went there in 1959 because of
a deep concern for problems of
childhood malnutrition in the developing
world and the desire to
become professionally involved
in seeking appropriate solutions.
The Institute had a newly created
program led by William Henry
Sebrell, one of the pioneer nutritionists
of the 20th century. The
Institute’s objective was to train
students to analyze, understand
and seek solutions to malnutrition
in the developing world in a holistic
context (15). My academic
training within this environment
and the opportunity to do my
thesis research in an international
setting among malnourished children
set the tone for the rest of
my professional career.
2006: Where are we
today – after 4½
decades?
Prevalence
No doubt, we have a greater
appreciation of the magnitude
of the global problem and the
epidemiological factors, in addition
to diet, that contribute to
its existence. The Micronutrient
Report published in 2001(16)
placed the magnitude of the
problem among preschool-aged
children at 75 – 140 million; earlier
estimates by the WHO placed the
prevalence as high as 230 million
(17). These prevalence data are
based on clinical eye signs and/or
low blood vitamin A levels from a
database that is far from representative
and firm. Nonetheless,
The Micronutrient Report also
noted a trend toward improvement
since 1980 in most regions
of the world, particularly since
1990, a period when large-scale
periodic vitamin A distribution programs
were expanding. Indeed,
on the public health level, intervention
by periodic distribution
of high-dose vitamin A supplements
now covers an estimated
70% of preschool-aged children
in 40 countries with at least one
dose of vitamin A annually, and
about 1/3 of these 40 countries
have achieved 70% coverage
with the required two doses (18).
However, now we know that the
problem extends beyond the preschool
years to pregnant women
whose health and survival also are
compromised in countries where
deficiency is common (19). The
magnitude of deficiency among
pregnant women, however, is
largely unknown and there are few
targeted prevention programs in
effect that reach these vulnerable
women.
Metabolism and methods
Knowledge of the metabolism of
vitamin A and carotenoids has
advanced dramatically since
1960. The active forms and functions
of vitamin A are established:
retinol in the visual system and
retinoic acid in normal growth
and development by modulation
of gene actions. And new knowledge
of non-provitamin A roles of
carotenoids in the moderation of
degenerative diseases is evolving
as definitive analytical techniques
allow for tracing the metabolism
of individual carotenoids. Quantitative
analytical methods for
retinoids are well advanced (20)
and this has contributed to a
variety of new field assessment
methods, including a more objective
and reproducible meas-