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Natural food sources of vitamin A and provitamin A


S. L. Booth, T. Johns, and H. V. Kuhnlein

 


Overview of natural sources


The new recommended nutrient intakes (RNI) of vitamin A published by FAO/WHO [1] are two-tiered (table 1), with a basal level, corresponding to a recommended intake to prevent deficiency, and a safe level, similar to the recommended dietary allowance (RDA) set for the United States [2], which corresponds to an intake recommended for adequate liver storage of the vitamin [1, 3, 4] The dietary sources of vitamin A are of two categories: vitamin A. or retinol, also known as preformed vitamin A; and provitamin A, which refers to those carotenoid precursors that are biologically active as retinol.

TABLE 1. Recommended dietary intakes of vitamin A (RE)

 

Basal

Safe

Infants 180 350
Children
1-6 years 200 400
6-15 years 250-350 400-600
Males 300-400 500-600
Females 270-330 500
Pregnancy + 100 + 100
Lactation + 180 + 350

Source: Ref .1 .

The parent compound of vitamin A is all-trans retinol, which is an isoprenoid compound found in animal tissue [4-6]. Vitamin A is the generic term for all -ionine derivatives, excluding the carotenoids. The major storage form' retinyl palmitate, is an ester of a fatty acid chain, 90% of which is stored in the liver. Carotenoids are a class of more than 400 known naturally occurring pigments found in certain fruits. vegetables. oils. and animal foods such as egg yolk and shrimp, of which approximately 50 are known to be biologically active as vitamin A [7, 8]. These carotenoids, of which -carotene has the highest known vitamin A activity, are converted to vitamin A by oxidative cleavage [9]. Some carotenoids are absorbed intact and then deposited in various body tissues, including fat deposits, skin, shell, milk, and eggs.

Retinol is found exclusively in animal foods, whereas carotenoids are found primarily in plant foods. Their occurrence in animal foods is dietary in origin [6]. It is estimated that the median dietary intake of vitamin A in the United States is composed of approximately 25% provitamin A and 75% preformed vitamin A [3], with dairy products and fortified foods being the major contributing dietary items. In contrast, studies from developing regions suggest that up to 80% of the dietary intake of vitamin A comes from provitamin A food sources [6]. A common observation in the literature is the prohibitive cost of preformed vitamin A food sources for most regions where xerophthalmia is a documented health problem.

The richest known sources of provitamin A are the palm oils. Red palm oil, a common cooking product in west Africa, is usually cited as having the highest concentration of provitamin A activity [10]. However, recent studies indicate that the oil of the buriti palm tree has a tenfold greater concentration of vitamin A activity than red palm oil [11]. The highest levels of preformed vitamin A are found in animal and fish livers and fish oils [12]. Other food sources of the vitamin include the following:

provitamin A

preformed vitamin A

These categories are generalizations, because variations between and within species in both provitamin A and preformed vitamin A are very large. as will be discussed in greater detail later.

White roots and tubers and whole grains are considered very low in provitamin A content, and it is often observed that xerophthalmia is more prevalent in rice-consuming areas when vitamin A-rich foods are not introduced early in the weaning stage [13].

Colour intensity, however, is not necessarily a reliable indicator of biologically active carotenoids. For example, the chlorophyll of green leafy vegetables masks the carotenoid pigmentation, yet as a group these vegetables are considered excellent sources of provitamin A [6]. Moreover, as mechanisms of carotenoid physiology and biochemistry are being clarified, and with the introduction of high performance liquid chromatography (HPLC) for the analysis of the carotenoid profile of these foods, many previous assumptions about natural food sources of provitamin A need to be revised.

Storage of retinol in animal species is not evenly distributed. The richest stores are found in the kidneys and liver [12]. Retinol is also stored in the intestinal walls of fish, in the body fat of eels, and in the eyes of certain species of shrimp. With the exception of fowl, meat products, including beef and pork, do not contain significant quantities of preformed vitamin A.


Published values


The values in tables 2-8 have been compiled to present a sample of the reported vitamin A activity of selected foods from the current food composition literature. In a number of cases, several species are aggregated to demonstrate differences in nutrient content. Foods devoid of or low in vitamin A activity have been included to demonstrate trends in food categories and the use of colour as a general indicator of activity.

TABLE 2. Published values for vitamin A activity in green vegetables, algae, and flowers

  Description CE TA Ref
Amaranth leaf, raw 5,400-9,260 900- 1.543 14. 15
leaf & flowers, raw 2,538 423 14
Beet leaf, raw 2,927 487 14
Burclover leaf & flowers, raw 5,196 866 14
Cabbage green, leaf, raw 60 10 16
red, leaf, raw 18 3 16
Carrot leaf, raw 7,200 1,200 14
Cassava leaf, raw 3,000 500 17
Chayote shoot, raw 1,000 166 18
shoot, boiled 400 66 18
Chicory leaf, raw 600-2,1600 100-360 16
Chinese leaf leaf, raw 78 13 16
Cowpea leaf, raw 4,500 750 18
Dandelion leaf, raw 7,200-8,200 1,200-1,367 16
Egyptian mallow leaf, raw 9,000 1,500 14
Flowers (diverse species) flower, raw 20-3.600 3-353 19
Goosefoot leaf, raw 5,80U 966 14
Jute, potherb leaf, raw 6,400 1,066 14
Hare's lettuce leaf, raw 1,430 238 17
Indian mustard leaf, raw 1.800 300 14
Kale leaf, raw 900-7,580 150-1,263 16
Lambsquarters leaf, raw 3.840 640 20
Lettuce leaf, raw 1,950 325 17
Okra leaf, raw 730 121 17
Pumpkin leaf, raw 1,000 166 17
Seaweed (diverse species) raw 20-1,490 3-248 21
dried 30- 12,500 5- 1,083 21
Sweet potato leaf, raw 1,100-2,700 183-450 21, 22
leaf. boiled 1.745 291 21
Taro leaf, raw 5.535 922 21
leaf, boiled 4,695 783 21
Watercress leaf, raw 1,200-4,000 200-667 16
Wonderberry leaf, raw 4,800 800 14
Viper's grass leaf, raw 1,900-2,200 317-367 14, 16

TABLE 3. Published values for vitamin A activity in fruits

  Description CE TA Ref.
Akee raw 560 93 16
Apple raw 43 7 16
Apricot raw 450-3,500 75-583 14, 16
dried 1,260-6,540 210-1,090 14, 16
Avocado raw 60-532 10-88 16, 17
Banana yellow, raw 60-130 10-21 19
red, raw 90 15 19
Blueberry raw 60-170 10-28 16
Cashew fruit raw 760 127 16
Chile pepper raw 459 77 14
Currant white, raw 0 0 16
black, raw 7-200 1-33 16.23
Guava raw 80-400 13-67 14, 16
Loquat raw 1,580 263 14
Mandarin juice 250 42 16
Mango ripe, raw 708-2,400 118-400 14, 17, 24
unripe, raw 60 10 17
dried 4,400-5,261 733877 25
Muskmelon raw 620 103 14
Papaya raw 300-2.500 50-417 17, 26
Persimmon raw 3,000 500 14
Plantain raw 475 79 21
boiled 345 58 21
Raspberry juice 60 10 16
Sapote (diverse species) raw 48-l00 8-17 16, 24
Tamarillo raw 460-2,100 77-350 16, 24
Watermelon raw 50-350 8-58 16, 17
West Indian cherry raw 0-240 0-40 16. 23

TABLE 4. Published values for vitamin A activity in plant storage organs and seeds

  Description CE TA Ref.
Bitter gourd raw 17,040 2,840 27
cooked 13.260 2,210 27
Carrot raw 3,890-21,000 648-3,500 14, 16
dried 36,000-135,000 6,000-22,500 16
pickled 123-1,063 20-177 14, 28
juice 2,620 437 16
Cassava raw 5-35 1 -6 16
Finger millet flour 25 4 17
Maize yellow, raw 360 60 17
yellow, dried 125 20 17
white, dried 0 0 17
Potato white, raw 2-20 trace-3 16
Rice parboiled 0 0 17
Summer squash raw 82 14 14
Sweet potato white, raw 35 6 21
yellow, raw 300-4,620 50-770 16, 21
Turnip yellow, raw 1,620 270 27
yellow, cooked 1,320 220 27
Winter squash raw 552 92 14

TABLE 5. Published values for vitamin A activity in plant oils

  CE TA Ref.
Buriti palm oil 304.000 50,667 11
Cocount oil 0 0 16
Olive oil 25 4 29
Palm kernel oil 22 4 30
Red palm oil 12,210-87,881 2,035-24,647 30, 31
Seed oil (diverse species) 12-684 2- 114 30

TABLE 6. Published values for vitamin A activity in milk, milk products, and eggs

  Description RE CE TA Ref.
Buffalo milk whole 64 0 64 16
Chicken egg whole 260 0 260 32
white 0 0 0 16
yolk 870 0 870 32
Cow milk 3.3% butter fat 27-34 14-22 29-38 16
Duck egg whole 540 1,200 740 16
Ghee goat milk 236 0 236 33
cow milk 270 230 308 14
Goat milk whole 19-71 0 19-71 33
Tabriz cheese - 0 288 48 14
Teleme cheese fresh 56 0 56 34
pickled 48 0 48 34
Yoghurt plain 23 0 23 32

TABLE 7. Published values for vitamin A activity in fish

  Description RE CE TA Ref
Catfish raw 6-29 0 6- 29 12
Cod raw 8- 12 0 8- 12 12
oil 9,009 0 9,009 12
Eel raw 48- 180 0 48- 180 12
smoked 27- 180 0 27- 180 12
Freshwater fish
(diverse species) oil 9,000- 672,000 0 9,000- 672,000 12
Halibut raw 15-47 0 15-47 12
oil 15,000 0 15,000 12
Loche flesh 11 0 11 35
liver 8,690 0 8.690 35
Marine fish
(diverse species) oil 48,048-3000,00 0 48,048-300,00 12
Oyster raw 90-96 0 90-96 12
Requiem shark liver 143,000 30,000 148,000 14
Skate raw 3 0 3 12
Sole raw trace 0 trace 12
Tigerfish raw 2.737 0 2,737 14
pickled 2,668 0 2,668 14
Tuna raw 80-830 0 80-830 12

TABLE 8. Published values for vitamin A activity in organ meat and other animal products

  Description RE CE TA Ref.
Beef flesh, raw 24 5 25 17
heart, raw 40 10 41 17
kidney, raw 300 0 300 17
liver, raw 810 180 840 17
Caribou flesh, raw trace 0 trace 35
flesh, dried trace 0 trace 35
Chicken flesh, raw 10-74 0 10-74 14,16
heart, raw 9 0 9 16
liver, raw 6-20 0 6-20 16
Goat flesh, raw 0 0 0 17
liver, raw 13,500 2,800 13,967 14
Goose flesh, raw 44-97 0 44-97 16
liver, raw. 9,880 0 9,880 12
Narwhal blubber, raw 1,748 0 1,748 36
blubber, aged 1,004 0 1,004 36
blubber, boiled 2,193 0 2,193 36
Polar bear liver, raw 543,543-912,913 0 543,543-912,913 37
Ringed seal blubber, raw 717 0 717 36
blubber, boiled 371 0 371 36
eyes, raw 306 0 306 36
liver, raw 14,981 0 14,981 36
Sheep flesh, raw 0-45 0 0-45 16
Turkey flesh, raw 13 0 13 16

For simplicity and consistency, all food items are identified in the tables by their English common names as some of the references do not include scientific names. Because there is wide species-specific variation, the reader is referred to the original references for the scientific names when these are given. A range presented for more than one species is denoted by "diverse species."

The column headed "Description" specifies the part sampled when this information is available. gives other relevant identification of the food items such as colour, and indicates the method of sample preparation.

The units for vitamin A activity have been presented as retinol equivalents (RE) or, -carotene equivalents (CE) per 100 grams of edible portion. Conversion of international units (IU) to RE and calculation of total vitamin A activity (TA) in retinol equivalents will be discussed later. As these nutrient values include original data using various analytical techniques, values converted from IU or RE, and calculation of total vitamin A activity, they should be interpreted with caution.


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