Plant and algae are capable of synthesizing β-carotene. However, humans and animals are not capable of synthesizing β-carotene. But they are capable of converting β-carotene absorbed from their diets to vitamin A. The difference between humans and animals (white-fat mammals) in digesting or processing dietary β-carotene is that humans can absorb intact β-carotene (detected β-carotene in human circulation) ( Figure 1) whereas most white-fat animals cannot.1 Vitamin A formed from plant β-carotene eaten by animals, in addition to meeting their daily needs, is stored in animal tissues and organs (mainly in liver, egg yolk, milk, etc.). Through the intake of these foods originating from animals, humans can easily absorb their vitamin A content (preformed vitamin A). In addition, they still obtain sufficient vitamin A needs of about 0.5– 0.7 mg per day.2 About 2–3 eggs or 50–100 g of butter or 10 g of liver per day will be enough to satisfy the daily need for vitamin A (preformed). However, foods from animal origins are not always available or affordable for millions of people in various parts of the world. Therefore, plant foods, mainly dark-green / yellow vegetables or orange colored fruits rich in provitamin A carotenoids, containing mainly β-carotene, are usually the source of vitamin A for these populations. These populations who rely on provitamin A carotenoids as their sole vitamin A source must convert the pro- vitamin A in their diets into vitamin A. If the population cannot effectively convert dietary β-carotene to vitamin A, or if they can- not obtain a sufficient amount of this to meet their daily dietary needs, the chronic lack will result in VAD.
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