What it is
Vitamin A includes preformed retinoids and provitamin A carotenoids; these forms differ in conversion, biological activity, and excess-intake risk.
Core function and why it is studied
The core connection is the recognized physiological role described above. Research therefore examines vision, epithelial integrity, immune function, and nutrient adequacy, while supplement value still depends on baseline intake or status, the form used, and the outcome being measured.
What the evidence means
The physiological role is well established. Supplement benefit is most predictable when intake or status is inadequate; more is not automatically better.
How to compare products
Compare the exact nutrient form, amount per serving, Daily Value where applicable, elemental amount for minerals, and total intake from other products.
