Provide a detailed explanation of the role of [vitamin A] in human health, including its sources and how it is absorbed in the body. Your response should contain at least 3 paragraphs. Paragraphs are separated with the markdown divider: ***. Highlight at least 2 sections in your answer with markdown, i.e. *highlighted section*. In your response, the word [vitamin] should appear at least 3 times.

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