1 How Dietary Deficiency Studies Have Illuminated the Many Roles …
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cancer progression. This large body of work will not be reviewed here, but the reader
is referred to these selected references for an introduction to these areas of research
(Brun et al. 2016; Trasino et al. 2015; Trasino and Gudas 2015; Oliveira et al. 2018;
Reza Dorosty-Motlagh et al. 2016; Okayasu et al. 2016; French et al. 2000; Li et al.
2005; Bernstein and Harris 1984; Stehr et al. 1985; Penny et al. 2016).
Relevance
Sherman and Trupp (1949) noted: (1) “The intake level of 3 IU of vitamin A per gram of dry
food, or about 0.8 IU per calorie, meets a standard of minimal adequacy. Human subjects
have subsisted at such levels for many months without showing signs of deficiency, and a
laboratory rat family is thriving in the 67th generation at this level.” and (2) “Yet while such
a level of vitamin A intake thus clearly meets a certain minimal standard of adequacy it does
not, in the long-term test of a lifetime, support the optimal life history of which the individual
is capable, for with double the allowance (rats on Diet 360, with 6 IU of vitamin A per gram
of dry food), the length of life was increased about 5 per cent in males and about 10 per cent
in females.” (Eglitis and Sherman 1983; Sherman and Trupp 1949).
Understanding the biology and biochemistry of vitamin A is highly relevant to the
health of all vertebrates, including farm animals, such as chickens (Parrish et al.
1963), cattle (Harris et al. 2018; Wang et al. 2016), pigs (Zhao et al. 2016), fish (La
Frano et al. 2018), and humans (Sauvant et al. 2012). The World Health Organization, UNICEF, and other organizations that monitor vitamin A deficiency in world
populations see vitamin A deficiency as a major health problem for human populations with inadequate diets. Pregnant and breast feeding women and very young
children are at greatest risk because of the requirement for higher levels of vitamin
A to support fetal and early development. Individuals with reduced serum retinol
concentrations (<0.70 μmol/l) and/or night blindness are defined as being vitamin A
deficient). Often these individuals have severe infections, diarrhea, and respiratory
diseases that depress appetite and absorption (World Health Organization 2009).
While vitamin A deficiency studies have led to the incontrovertible conclusion
that vitamin A is required for vertebrate life, the prediction that supplementing deficient organisms with “off-the-shelf” vitamin A will restore normal function does
not necessarily follow. To some, it has become evident that high dose vitamin A
supplementation may not produce sustained improvement in the vitamin A deficient
status of children and adults (Benn 2017; Mason et al. 2018). As a result, one recommendation is to use dietary interventions, rather than supplementation, to ameliorate
vitamin A deficiency syndromes.
That supplementation with vitamin A may not alleviate clinical deficiency is
an illustration of the complex mechanisms of vitamin A action. Vertebrates have
evolved complicated processes to digest, absorb, transport, convert, and present vitamin precursors and derivatives (carotenoids and retinoids) to downstream molecules
that use these molecules to carry out vitamin A-dependent processes (Asson-Batres
and Rochette-Egly 2014, 2016). It could be that direct supplementation with high
19
cancer progression. This large body of work will not be reviewed here, but the reader
is referred to these selected references for an introduction to these areas of research
(Brun et al. 2016; Trasino et al. 2015; Trasino and Gudas 2015; Oliveira et al. 2018;
Reza Dorosty-Motlagh et al. 2016; Okayasu et al. 2016; French et al. 2000; Li et al.
2005; Bernstein and Harris 1984; Stehr et al. 1985; Penny et al. 2016).
Relevance
Sherman and Trupp (1949) noted: (1) “The intake level of 3 IU of vitamin A per gram of dry
food, or about 0.8 IU per calorie, meets a standard of minimal adequacy. Human subjects
have subsisted at such levels for many months without showing signs of deficiency, and a
laboratory rat family is thriving in the 67th generation at this level.” and (2) “Yet while such
a level of vitamin A intake thus clearly meets a certain minimal standard of adequacy it does
not, in the long-term test of a lifetime, support the optimal life history of which the individual
is capable, for with double the allowance (rats on Diet 360, with 6 IU of vitamin A per gram
of dry food), the length of life was increased about 5 per cent in males and about 10 per cent
in females.” (Eglitis and Sherman 1983; Sherman and Trupp 1949).
Understanding the biology and biochemistry of vitamin A is highly relevant to the
health of all vertebrates, including farm animals, such as chickens (Parrish et al.
1963), cattle (Harris et al. 2018; Wang et al. 2016), pigs (Zhao et al. 2016), fish (La
Frano et al. 2018), and humans (Sauvant et al. 2012). The World Health Organization, UNICEF, and other organizations that monitor vitamin A deficiency in world
populations see vitamin A deficiency as a major health problem for human populations with inadequate diets. Pregnant and breast feeding women and very young
children are at greatest risk because of the requirement for higher levels of vitamin
A to support fetal and early development. Individuals with reduced serum retinol
concentrations (<0.70 μmol/l) and/or night blindness are defined as being vitamin A
deficient). Often these individuals have severe infections, diarrhea, and respiratory
diseases that depress appetite and absorption (World Health Organization 2009).
While vitamin A deficiency studies have led to the incontrovertible conclusion
that vitamin A is required for vertebrate life, the prediction that supplementing deficient organisms with “off-the-shelf” vitamin A will restore normal function does
not necessarily follow. To some, it has become evident that high dose vitamin A
supplementation may not produce sustained improvement in the vitamin A deficient
status of children and adults (Benn 2017; Mason et al. 2018). As a result, one recommendation is to use dietary interventions, rather than supplementation, to ameliorate
vitamin A deficiency syndromes.
That supplementation with vitamin A may not alleviate clinical deficiency is
an illustration of the complex mechanisms of vitamin A action. Vertebrates have
evolved complicated processes to digest, absorb, transport, convert, and present vitamin precursors and derivatives (carotenoids and retinoids) to downstream molecules
that use these molecules to carry out vitamin A-dependent processes (Asson-Batres
and Rochette-Egly 2014, 2016). It could be that direct supplementation with high