Vitamin C and Your Genes
Vitamin C and Your Genes
Why cellular delivery, not intake, is the key to tolerance.
When most people think about Vitamin C, they think in terms of how much they’re taking: more citrus, bigger supplements, higher grams. But the truth is a lot more personal than that.
Vitamin C tolerance is not determined by how much you ingest. It is determined by how efficiently vitamin C is transported into tissues. Two people can consume the same amount, yet one becomes functionally replete while the other remains deficient at the cellular level.
That’s not a willpower issue. It’s not “your body being weird.” It’s biology—and for many people, it’s genetics.
The genes that control Vitamin C delivery
Two key genes—SLC23A1 and SLC23A2—encode the sodium-dependent vitamin C transporters SVCT1 and SVCT2.
These transporters are not about how much Vitamin C is present in food. They regulate movement of ascorbic acid from the gut and bloodstream into cells, including:
- Immune cells
- Adrenal tissue
- Brain
- Connective tissue
- Mitochondria
When transporter function is reduced, intake can look adequate while intracellular levels remain low.
Why “bowel tolerance” can be misleading
This is where a lot of well-meaning people get thrown off. Loose stools do not necessarily mean the body has enough vitamin C. In many cases, vitamin C is accumulating in the intestinal lumen because tissues are not pulling it in efficiently.
The limiting factor is delivery, not absorption from food alone. If someone “hits bowel tolerance” quickly, it doesn’t automatically mean they’re saturated—it may mean their tissues aren’t able to retain and use what’s coming in.
Different reactions, same underlying problem
Some people hit bowel tolerance quickly and feel overstimulated, nauseated, or reactive. Others tolerate very high doses but feel little benefit until intake reaches gram levels.
These are not opposing problems. They are different expressions of the same issue: Tissue saturation is not keeping pace with intake. Simply pushing higher and higher doses often doesn’t solve it.
What actually helps raise Vitamin C tolerance
Raising tolerance is about improving the conditions required for vitamin C to move into cells. Here are the most common “bottlenecks”:
1) Sodium matters (a lot)
Vitamin C transport is sodium dependent. Chronically low sodium intake, adrenal strain, or altered fluid regulation can directly impair transporter activity.
2) Cell membranes must be healthy
Transporters sit within cell membranes. Poor fatty acid balance, damaged membranes, or insufficient cholesterol reduce transporter efficiency.
3) Oxidative stress burns through Vitamin C
Oxidative stress increases turnover. Iron excess, chronic inflammation, infections, and environmental toxins all consume vitamin C rapidly.
4) Blood sugar increases demand
Glucose competes with vitamin C at the cellular level. Blood sugar instability can significantly raise vitamin C demand even when intake appears generous.
Practical steps for “functional absorption”
- Smaller, divided doses
- Adequate sodium support
- Membrane integrity (healthy fats)
- Address iron excess
- Use pure Ascorbic Acid
As tissues begin to retain vitamin C, tolerance naturally rises. Stool tolerance shifts upward not because the gut adapted, but because cells finally started holding onto vitamin C.
