In a majority of people, the carotene-to-retinol conversion is severely compromised, and in some it may be quite negligible. This is particularly true for infants, diabetics, and those with compromised bile production.
While Vitamin A is found in many fruits , green vegetables ,like carrots ,spinach it is in the form beta carotenoids and is not usable by the body, and needs to be activated to the usable form retinol, studies show huge differences in the conversion rate that you may be only getting 3-4% from plant sources of Vitamin A – Study Showing Conversion Rates
Your body’s ability to convert carotenoids into bioavailable vitamin A also depends on your diet in general. If you’re on a low-fat diet, your conversion rate is virtually guaranteed to be inadequate.