3 Vitamins C. A Northrop-Clewes and D. I. Thurnham, University of Ulster 3.1 Introduction Vitamins are classically defined as a group of organic compounds required in very mall amounts for the normal development and functioning of the body. They are not synthesised by the body, or only in insufficient amounts, and are mainly obtained through food(Machlin and Huni, 1994) There are thirteen vitamins: four are fat-soluble, namely vitamins a (retinol). D(calciferols), E(tocopherols) and K(phylloquinone and menaquinones) and nine are water-soluble, vitamin C (ascorbate)and the B-complex made up of vita- mins B,(thiamin), B,(riboflavin), B,(pyridoxal, pyridoxamine and pyridoxine) B12(cobalamin), folic acid, biotin, niacin and pantothenic acid. No single food contains all of the vitamins and therefore a balanced and varied diet is necessary for an adequate intake 3.1.1 Dietary reference values Prior to 1991 relatively few micro-nutrients were covered in official British government publications on energy, protein, vitamin and mineral requirements Whitehead, 1991). The 1979 definition of the Recommended Dietary Allowance (RDA) was 'the average amount of the nutrient which should be pre head in a group of people if the needs of practically all members of the group to be met. However, the rda values have always been derived depending on whether energy or nutrients were being considered. In 1987 the Committee on Medical Aspects of Food Policy(COMA)convened a panel to review the old RDAs of energy, fat, non-starch polysaccharides, sugars, starches, protein, vitamins and minerals for groups of people in the United
3 Vitamins C. A. Northrop-Clewes and D. I. Thurnham, University of Ulster 3.1 Introduction Vitamins are classically defined as a group of organic compounds required in very small amounts for the normal development and functioning of the body. They are not synthesised by the body, or only in insufficient amounts, and are mainly obtained through food (Machlin and Huni, 1994). There are thirteen vitamins: four are fat-soluble, namely vitamins A (retinol), D (calciferols), E (tocopherols) and K (phylloquinone and menaquinones) and nine are water-soluble, vitamin C (ascorbate) and the B-complex made up of vitamins B1 (thiamin), B2 (riboflavin), B6 (pyridoxal, pyridoxamine and pyridoxine), B12 (cobalamin), folic acid, biotin, niacin and pantothenic acid. No single food contains all of the vitamins and therefore a balanced and varied diet is necessary for an adequate intake. 3.1.1 Dietary reference values Prior to 1991 relatively few micro-nutrients were covered in official British government publications on energy, protein, vitamin and mineral requirements (Whitehead, 1991). The 1979 definition of the Recommended Dietary Allowance (RDA) was ‘the average amount of the nutrient which should be provided per head in a group of people if the needs of practically all members of the group are to be met.’ However, the RDA values have always been derived differently depending on whether energy or nutrients were being considered. In 1987 the Committee on Medical Aspects of Food Policy (COMA) convened a panel to review the old RDAs of energy, fat, non-starch polysaccharides, sugars, starches, protein, vitamins and minerals for groups of people in the United
Vitamins 35 Kingdom(Department of Health and Social Security, 1979). The panel changed e 'requirements'nomenclature, and whereas most sets of RDAs provided only a single value for the micronutrients, the new Dietary Reference Values(DRVs) set three levels of values for each age and sex grouping. The aim was to describe the range of requirements in different individuals more adequately. The estimated average requirement(EAR)represents the mean requirement of the average indi- vidual, the reference nutrient intake(RND) is nominally set at the mean plus two standard deviations(2 SD), and the lower reference nutrient intake (LRND is nominally the mean minus an estimated 2 SD. The three parameters describe the spread of requirements It was thought that the EAr might be increasingly used in food labelling thus providing all dietary constituents in food with a common baseline for compari but the rni is the key value for clinical and health purposes. Table 3. 1 is the ummary table of the RNI for six B vitamins, plus vitamins A, C and D. within the context of the UK, the reason for considering only 9 out of the 13 vitamins was that the panel thought only those micronutrients for which some possibility of deficiency existed needed to be dealt with in such detail. In addition, there was insufficient information for pantothenic acid, biotin and vitamins E and K to provide a complete data set of recommendations, hence only single safe intake recommendations were considered (Whitehead, 1992) Table 3.2 gives a summary of the principal food sources and major function of each vitamin 3.2 Vitamin A Vitamin A can be obtained in two forms: pre-formed retinol, usually as retinyl esters, or as provitamin A carotenoids, such as a-and p-carotene and a-and B- cryptoxanthin. In the UK about a quarter to a third of dietary vitamin A is obtained from fruits and vegetables, the majority of this as B-carotene. In many develop- ing countries up to 100%o of dietary intake can be from plant sources and in these communities, where exposure to infection is usually high, it is most likely to find vitamin A deficiency disorders (VADD). One of the earliest clinical signs of vitamin A deficiency (VAD) is night blindness(XN), an impaired ability to see in dim light. Severe deficiency produces partial or total blindness. The most vul nerable groups to VADD are infants and young children and pregnant and lac tating women 3.3 Vitamin a deficiency disorders (VadD) Vitamin A deficiency disorders may be defined as a level of depletion of total body stores of retinol and of its active metabolites such that normal physiologic function is impaired. Dietary intake does not accurately reflect status since intake may fluctuate considerably in different seasons and the body only stores vitamin
Kingdom (Department of Health and Social Security, 1979). The panel changed the ‘requirements’ nomenclature, and whereas most sets of RDAs provided only a single value for the micronutrients, the new Dietary Reference Values (DRVs) set three levels of values for each age and sex grouping. The aim was to describe the range of requirements in different individuals more adequately. The estimated average requirement (EAR) represents the mean requirement of the average individual, the reference nutrient intake (RNI) is nominally set at the mean plus two standard deviations (2 SD), and the lower reference nutrient intake (LRNI) is nominally the mean minus an estimated 2 SD. The three parameters describe the spread of requirements. It was thought that the EAR might be increasingly used in food labelling thus providing all dietary constituents in food with a common baseline for comparison but the RNI is the key value for clinical and health purposes. Table 3.1 is the summary table of the RNI for six B vitamins, plus vitamins A, C and D. Within the context of the UK, the reason for considering only 9 out of the 13 vitamins was that the panel thought only those micronutrients for which some possibility of deficiency existed needed to be dealt with in such detail. In addition, there was insufficient information for pantothenic acid, biotin and vitamins E and K to provide a complete data set of recommendations, hence only single safe intake recommendations were considered (Whitehead, 1992). Table 3.2 gives a summary of the principal food sources and major functions of each vitamin. 3.2 Vitamin A Vitamin A can be obtained in two forms: pre-formed retinol, usually as retinyl esters, or as provitamin A carotenoids, such as a- and b-carotene and a- and bcryptoxanthin. In the UK about a quarter to a third of dietary vitamin A is obtained from fruits and vegetables, the majority of this as b-carotene. In many developing countries up to 100% of dietary intake can be from plant sources and in these communities, where exposure to infection is usually high, it is most likely to find vitamin A deficiency disorders (VADD). One of the earliest clinical signs of vitamin A deficiency (VAD) is night blindness (XN), an impaired ability to see in dim light. Severe deficiency produces partial or total blindness. The most vulnerable groups to VADD are infants and young children and pregnant and lactating women. 3.3 Vitamin A deficiency disorders (VADD) Vitamin A deficiency disorders may be defined as a level of depletion of total body stores of retinol and of its active metabolites such that normal physiologic function is impaired. Dietary intake does not accurately reflect status since intake may fluctuate considerably in different seasons and the body only stores vitamin Vitamins 35
Table 3.1 Reference nutrient intakes(RND) for Age Thiamin Riboflavin Vitamin B Vitamin Bu Folate VitaminC Vitamin A VitaminD 8 ug/ ug/ 0-6 months 0.2 0.4 3.0 0.2 g25500 350 8.5 7-9 months 0.2 0.4 0.3 350 10-12 months 0.3 350 1-3 years 0.5 0.6 0.7 4-6 years 0. 0.8 0.9 0.8 0000 500 7-10 years 2 1.0 Males 11-14 0.9 600 15-18 1.3 18 700 9-50 1.0 1.3 17 1.5 20040 700 0.9 1.5 Females 0.7 0 200 600 15-18 years 1.1 14 600 19-50 years 0.8 1.1 13 1.5 600 0.8 1.2 1.5 Pregnancy/Lactation +0. 1 +0.3 +100+10 10 H4 months +0.2 +0.5 +0.5 +60 400000 350 4+mo +0.2 +0.5 2 +0.5 +60 350 #f Based on protein providing 14.7%o of EAR for energy. For last trimester only. No increment After age 65 the RNI is 10.0ugd for men and womer DEPARTMENT OF HEALTH 1991
36 The nutrition handbook for food processors Table 3.1 Reference nutrient intakes (RNI) for vitamins Age Thiamin Riboflavin Niacin Vitamin B6 Vitamin B12 Folate Vitamin C Vitamin A Vitamin D mg/d mg/d mg/d mg/d# mg/d mg/d mg/d mg/d mg/d 0–6 months 0.2 0.4 3.0 0.2 0.3 50 25 350 8.5 7–9 months 0.2 0.4 4.0 0.3 0.4 50 25 350 7 10–12 months 0.3 0.4 5.0 0.4 0.4 50 25 350 7 1–3 years 0.5 0.6 8.0 0.7 0.5 70 30 400 7 4–6 years 0.7 0.8 11 0.9 0.8 100 30 500 – 7–10 years 0.7 1.0 12 1.0 1.0 150 30 500 – Males 11–14 years 0.9 1.2 15 1.2 1.2 200 35 600 – 15–18 years 1.1 1.3 18 1.5 1.5 200 40 700 – 19–50 years 1.0 1.3 17 1.4 1.5 200 40 700 – 50 + years 0.9 1.3 16 1.4 1.5 200 40 700 *** Females 11–14 years 0.7 1.1 12 1.0 1.2 200 35 600 – 15–18 years 0.8 1.1 14 1.2 1.5 200 40 600 – 19–50 years 0.8 1.1 13 1.2 1.5 200 40 600 – 50 + years 0.8 1.1 12 1.2 1.5 200 40 600 *** Pregnancy/Lactation +0.1* +0.3 ** ** ** +100 +10 +100 10 0–4 months +0.2 +0.5 +2 ** +0.5 +60 +30 +350 10 4 + months +0.2 +0.5 +2 ** +0.5 +60 +30 +350 10 # Based on protein providing 14.7% of EAR for energy. * For last trimester only. ** No increment. *** After age 65 the RNI is 10.0mg/d for men and women. DEPARTMENT OF HEALTH 1991
Table 3.2 Food sources and major functions of principal vitamins Vitamin Principal food sources Major functions in the body Vitamin A Animal sources: liver, egg yol whole milk, butter, cheese. Helps to keep muco Plant sources(as provitamin A): carrots, yellow and dark green resistance to infections; essential for vision: promotes bones and leafy vegetables, pumpkin, apricots, melon, red palm oil. tooth development. Vegetable consumption may be protective gainst certain cancers Vitamin D Fish-liver oils(sardine, herring, salmon, mackerel), eggs, meat, Promotes hardening of bones and teeth, increases the absorption of calcium sources:nuts,seeds, whor a, palm, corn, sunflower etc). Other Protects vitamins A and C and fatty acids; prevents damage to Vitamin E Vegetable oils(peanut grains, leafy green vegetables. ell membranes Antioxidant itamin K Green leafy vegetables, soybeans, beef liver, green tea, egg Helps blood to clot. May play a role in bone health. yolks, potatoes, oats, asparagus, cheese. Vitamin C Citrus fruits, sweet peppers, parsley, cauliflower, potatoes Formation of collagen. wound healt strawberries, broccoli, mango, Brussels sprouts vessels, bones, teeth; absorption of production of brain hormones, immune factors; antioxidant Thiamin Dried brewers yeast, animal products, whole grains, nuts, Helps release energy from foods; promotes normal appetite (B pulses, dried legumes. mportant in function of nervous system. Folate Main sources: liver, dark green leafy vegetables, beans, wheat Aids in protein metabolism; promotes red blood cell formation germ and yeast. Other sources: egg yolk, beet, orange juice, prevents birth defects of spine, brain; lowers homocysteine whole wheat bread levels and thus coronary heart disease risk Cobalamins Animal products(particularly liver, kidneys, heart, brain) fish, Aids in building of genetic material; aids in development of (B12) eggs, dairy products. normal red blood cells; maintenance of nervous system. Vitamin B6 Chicken, liver of beef, pork, fish(tuna, trout, salmon, herring), Aids in protein metabolism, absorption; aids in red blood cell peanuts and walnuts, bread, whole-grain cereals. use ia Biotin Yeast, liver, kidney, egg yolk, soybeans, nuts and cereals. Helps release energy from carbohydrates; aids in fat synthesis. Pantothenic Yeast, liver, heart, brain, kidney, eggs, milk, vegetables, energy production; aids in form legumes, whole grain cereals. Niacin Yeast, liver, poultry, lean meats, nuts and legumes. Less in milk Energy production from foods; aids digestion, promotes normal and green leafy vegetables. appetite; promotes healthy skin, nerves Riboflavin Yeast, liver, milk and milk products, meat, eggs, and green Helps release energy from foods; promotes healthy skin and mucous membranes; possible role in preventing cataracts
Vitamins 37 Table 3.2 Food sources and major functions of principal vitamins Vitamin Principal food sources Major functions in the body Vitamin A Animal sources: liver, egg yolk, fish, whole milk, butter, cheese. Helps to keep mucosal membranes healthy, thus increasing Plant sources (as provitamin A): carrots, yellow and dark green resistance to infections; essential for vision; promotes bones and leafy vegetables, pumpkin, apricots, melon, red palm oil. tooth development. Vegetable consumption may be protective against certain cancers. Vitamin D Fish-liver oils (sardine, herring, salmon, mackerel), eggs, meat, Promotes hardening of bones and teeth, increases the absorption milk. of calcium. Vitamin E Vegetable oils (peanut, soya, palm, corn, sunflower etc). Other Protects vitamins A and C and fatty acids; prevents damage to sources: nuts, seeds, whole grains, leafy green vegetables. cell membranes. Antioxidant. Vitamin K Green leafy vegetables, soybeans, beef liver, green tea, egg Helps blood to clot. May play a role in bone health. yolks, potatoes, oats, asparagus, cheese. Vitamin C Citrus fruits, sweet peppers, parsley, cauliflower, potatoes, Formation of collagen, wound healing; maintaining blood strawberries, broccoli, mango, Brussels sprouts. vessels, bones, teeth; absorption of iron, calcium, folate; production of brain hormones, immune factors; antioxidant Thiamin Dried brewers yeast, animal products, whole grains, nuts, Helps release energy from foods; promotes normal appetite; (B1) pulses, dried legumes. important in function of nervous system. Folate Main sources: liver, dark green leafy vegetables, beans, wheat Aids in protein metabolism; promotes red blood cell formation; germ and yeast. Other sources: egg yolk, beet, orange juice, prevents birth defects of spine, brain; lowers homocysteine whole wheat bread. levels and thus coronary heart disease risk. Cobalamins Animal products (particularly liver, kidneys, heart, brain) fish, Aids in building of genetic material; aids in development of (B12) eggs, dairy products. normal red blood cells; maintenance of nervous system. Vitamin B6 Chicken, liver of beef, pork, fish (tuna, trout, salmon, herring), Aids in protein metabolism, absorption; aids in red blood cell peanuts and walnuts, bread, whole-grain cereals. formation; helps body use fats Biotin Yeast, liver, kidney, egg yolk, soybeans, nuts and cereals. Helps release energy from carbohydrates; aids in fat synthesis. Pantothenic Yeast, liver, heart, brain, kidney, eggs, milk, vegetables, Involved in energy production; aids in formation of hormones. acid legumes, whole grain cereals. Niacin Yeast, liver, poultry, lean meats, nuts and legumes. Less in milk Energy production from foods; aids digestion, promotes normal and green leafy vegetables. appetite; promotes healthy skin, nerves. Riboflavin Yeast, liver, milk and milk products, meat, eggs, and green Helps release energy from foods; promotes healthy skin (B2) leafy vegetables. and mucous membranes; possible role in preventing cataracts
38 The nutrition handbook for food processors A when the intake exceeds requirements. Tissue concentrations may be assessed by measuring serum or breast milk retinol, or by using the retinol dose response (RDR), modified retinol dose response (MRDR), or by dilution with stable iso- topes. Functional indicators include pupillary dark adaptometry(PDA), cor tival impression cytology(CIC), and xerophthalmia. 3.4 Bioavailability of provitamin carotenoids De Pee and West (1996) proposed that control of VADd depends to a large extent on an adequate supply of vitamin a and the vitamin A supply is determined Food intake x(pro)-vitamin A content x bioavailability/bioefficacy, where Bioavailability fraction of ingested nutrient available for normal physiological functions and storage(Jackson, 1997) Bioefficacy =efficiency of absorption and conversion of ingested nutrient to th active form e.g. B-carotene to retinol(van Lieshout et al, 2001) 3.4.1 Relationship between bioefficacy and vitamin A requirements The RNi for children up to 5 years of age is 400ug retinol equivalents(RE)/day, which can easily be met from the diet if animal foods are available e. g. 1 egg (50g) contains about 100ug RE, 25 g chicken liver contains 3000ug RE Plants also contribute to vitamin A intake e. g. I raw carrot(20g) contains 400ug B- carotene, a 70g portion of spinach contains 600ug B-carotene and with a bioef- ficacy of 100%o would supply 400 and 600ug RE respectively. But the pro-vitamin A carotenoids are absorbed less efficiently than retinol, that is, their bioefficacy is less than 100%o. Therefore the effective supply of vitamin A from fruits and vegetables is much lower than that from retinol in animal foods(van Lieshout et al, 2001). If I mole B-carotene(Fig. 3. 1) yields 2 moles retine then, using 100% bioefficacy, I umol (0.537ug) B-carotene would be absorbed and converted totally to 2umol (0.572ug) retinol, i.e. 0.537/0.572=0.94ug B- carotene is equivalent to l ug retinol. The results of the"Sheffield studies carried out by the Medical Research Council(MRC)during the Second World War pro- vided important information to establish the relative equivalency of carotenoids and retinol (Hume and Krebs, 1949). These and other studies suggested that 6ug B-carotene or 12 ug of other pro-vitamin A carotenoids in a mixed diet had the same activity as l ug retinol (FAO/WHO 1967). Therefore, according to FAO/WHO the bioefficacy of B-carotene in food is(100%*094)/6=16%. But in the 1990s evidence was accumulating that the bioefficacy of provitamin A carotenoids in fruit and vegetables was only 20-30% of the FAO/WHO estimates of 16%0. The efficiency with which B-carotene in dark green leafy vegetables (DGLV) is metabolised to vitamin a was re-examined and various bioconversic factors have been put forward
A when the intake exceeds requirements. Tissue concentrations may be assessed by measuring serum or breast milk retinol, or by using the retinol dose response (RDR), modified retinol dose response (MRDR), or by dilution with stable isotopes. Functional indicators include pupillary dark adaptometry (PDA), conjunctival impression cytology (CIC), and xerophthalmia. 3.4 Bioavailability of provitamin carotenoids De Pee and West (1996) proposed that control of VADD depends to a large extent on an adequate supply of vitamin A and the vitamin A supply is determined by: Food intake ¥ (pro)-vitamin A content ¥ bioavailability/bioefficacy, where Bioavailability = fraction of ingested nutrient available for normal physiological functions and storage (Jackson, 1997) Bioefficacy = efficiency of absorption and conversion of ingested nutrient to the active form e.g. b-carotene to retinol (van Lieshout et al, 2001). 3.4.1 Relationship between bioefficacy and vitamin A requirements The RNI for children up to 5 years of age is 400mg retinol equivalents (RE)/day, which can easily be met from the diet if animal foods are available e.g. 1 egg (50 g) contains about 100mg RE, 25 g chicken liver contains 3000mg RE. Plants also contribute to vitamin A intake e.g. 1 raw carrot (20 g) contains 400mg bcarotene, a 70 g portion of spinach contains 600mg b-carotene and with a bioef- ficacy of 100% would supply 400 and 600mg RE respectively. But the pro-vitamin A carotenoids are absorbed less efficiently than retinol, that is, their bioefficacy is less than 100%. Therefore the effective supply of vitamin A from fruits and vegetables is much lower than that from retinol in animal foods (van Lieshout et al, 2001). If 1 mole b-carotene (Fig. 3.1) yields 2 moles retinol then, using 100% bioefficacy, 1mmol (0.537mg) b-carotene would be absorbed and converted totally to 2mmol (0.572mg) retinol, i.e. 0.537/0.572 = 0.94mg bcarotene is equivalent to 1mg retinol. The results of the ‘Sheffield’ studies carried out by the Medical Research Council (MRC) during the Second World War provided important information to establish the relative equivalency of carotenoids and retinol (Hume and Krebs, 1949). These and other studies suggested that 6mg b-carotene or 12mg of other pro-vitamin A carotenoids in a mixed diet had the same activity as 1mg retinol (FAO/WHO 1967). Therefore, according to FAO/WHO the bioefficacy of b-carotene in food is (100% * 0.94)/6 = 16%. But in the 1990s evidence was accumulating that the bioefficacy of provitamin A carotenoids in fruit and vegetables was only 20–30% of the FAO/WHO estimates of 16%. The efficiency with which b-carotene in dark green leafy vegetables (DGLV) is metabolised to vitamin A was re-examined and various bioconversion factors have been put forward: 38 The nutrition handbook for food processors