Vitamin C Intake Needs

SLC23A1 and SLC23A2 code for SVCT1 and SVCT2 — the transporters that move vitamin C from the gut into the bloodstream and from blood into cells. Unlike most animals, humans can’t synthesize vitamin C — every molecule has to come from food and pass through these transporters.

Carriers of common SLC23A1/SLC23A2 reduced-activity variants are associated with lower tissue vitamin C at standard dietary intakes — and may benefit from higher intake or smaller, more frequent doses to maintain protective tissue concentrations. Plasma vitamin C is poorly correlated with tissue status in this variant pattern.

Vitamin C absorbs best in divided doses (~250 mg per dose) because absorption saturates above that. Coffee, tea, and certain medications reduce uptake. Smoking nearly doubles vitamin C demand. Bioflavonoids in whole foods (citrus pith, peppers, berries) extend half-life and improve tissue retention compared to isolated ascorbic acid.

The "I take 1000 mg at once" approach loses most of the dose to excretion. Which SLC23 variant pattern you carry decides whether modest daily intake covers the need or whether spreading whole-food vitamin C across the day actually moves tissue levels.