Does Vitamin C Affect Blood Sugar?

What is vitamin C?

Vitamin C is a water-soluble nutrient that the body cannot produce, so it must be obtained through food or supplements. At lower doses, it acts as an antioxidant, protecting against oxidative stress, while at higher doses, it becomes a pro-oxidant.(1) In addition, vitamin C plays an important role in collagen production, which supports the healing of skin, bones, ligaments, and tissues.(2)

Can I take vitamin C on a ketogenic diet?

Yes. Oral vitamin C is used most often for immune support, while intravenous vitamin C therapy has shown efficacy against aggressive cancers as a complementary therapy.(2) It also is being used to treat Lyme disease(3) and autoimmune diseases like rheumatoid arthritis and lupus.(4) Intravenous vitamin C therapy for cancer may be particularly effective for those who also follow a ketogenic diet.(5)

Does vitamin C impact blood glucose levels?

Individuals undergoing high-dose IV vitamin C therapy, as prescribed by their healthcare provider, may experience falsely elevated blood glucose readings. This occurs because vitamin C can interfere with certain test strips, reacting with the electrode and causing a false increase in the glucose reading.(6)

Timing blood glucose and GKI (glucose ketone index) checks can help address this issue. Since intravenous vitamin C has a half-life of approximately two to three hours, it’s recommended to wait at least eight hours after an infusion before checking blood glucose and GKI to get an accurate reading.(7)

The half-life of oral vitamin C is similar to that of intravenous vitamin C.(8) So the same recommendation applies: wait at least eight hours after taking high-dose oral vitamin C before checking blood glucose and GKI.

Does vitamin C impact blood ketone levels?

Vitamin C is not known to affect ketone levels.

References

1. Review of high-dose intravenous vitamin C as an anticancer agent, Asia Pacific Journal of Clinical Oncology, 2014
2. Efficacy of Vitamin C Supplementation on Collagen Synthesis and Oxidative Stress After Musculoskeletal Injuries: A Systematic Review, Orthopedic Journal of Sports Medicine, 2018
3. High dose intravenous vitamin C for Lyme disease: a safety and tolerability study with an exploratory assessment of treatment efficacy, European Society of Medicine, 2025
4. Vitamin C Supplementation in the Treatment of Autoimmune and Onco-Hematological Diseases: From Prophylaxis to Adjuvant Therapy, International Journal of Molecular Sciences, 2024
5. Effect of high-dose intravenous ascorbic acid on cancer patients following ketogenic diet, The Journal of Cancer Research and Therapeutics, 2021
6. The effects of intravenous vitamin C on point-of-care glucose monitoring, Journal of Burn Care and Research, 2015
7. Interference of Intravenous Vitamin C With Blood Glucose Testing, Diabetes Care, 2014
8. On the effect of vitamin C intake on human health: How to (mis)interprete the clinical evidence, Redox Biology, 2020

Last updated by Franziska Spritzler, RD, CDCES, on February 11, 2025