As I understand, scientist currently think of Vitamin A as a family of organic compounds.

One finds beta-carotene in carrots. This needs to be converted to retinol for use in the human body. Apparently, people who lack the enzymes to convert beta-carotene into retinol don't see much benefit in beta-carotene.

Apparently vitamin A can be toxic if taken in large doses. So, the role of vitamin A is complex.