Vitamin C, or L-ascorbic acid, is crucial for life as it is involved in numerous processes including collagen synthesis, immune function, and antioxidant defense. Unlike most mammals that are able to produce tens of milligrams of ascorbic acid per day in the liver, humans are unable to synthesize this nutrient.
The primary reason for humans’ inability to endogenously produce vitamin C dates back to a specific mutation that occurred millions of years ago. This mutation in the GULO gene made humans the only primates incapable of synthesizing ascorbic acid, thereby rendering them entirely dependent on exogenous sources of the nutrient. It is critical to recognize how the human vitamin C mutation may impact health and outline strategies to prevent vitamin C deficiency, ensuring optimal levels of this essential nutrient in the body.
The Biological Paradox: Essential for Life, Yet Absent from Our DNA
In order to determine why our bodies are unable to produce ascorbic acid, it is necessary to consider the process by which other mammals generate it. For most species that populate Earth, vitamin C is not a vitamin, but rather a common by-product of the blood sugar metabolism.
The Four-Step Enzymatic Assembly Line
In most mammals, ascorbic acid is synthesized in the liver by a four-step biochemical pathway:
- UDP-Glucose Dehydrogenase: Catalyzes the formation of UDP-glucuronic acid from glucose.
- Glucuronate Reductase: Reduces UDP-glucuronic acid to form L-gulonate.
- SMP30 or Gluconolactonase: Generates L-gulonolactone.
- L-Gulonolactone Oxidase or GULO: Catalyzes the final reaction that produces L-ascorbic acid.
Humans are capable of synthesizing enzymes for the first three steps but lack the enzyme required for the last step.
The GULO Pseudogene Mutation
The main explanation for the human body’s inability to produce vitamin C relies on the particular mutation found on chromosome 8p21.2. This area houses the remnants of our GULO (L-gulonolactone oxidase) gene.
From Functional Gene to Pseudogene: The GULOP Mutation
In humans and other haplorhine primates, this gene was inactivated by structural errors:
- Frame-shift mutations and deletions leading to faulty reading frames.
- Stop codons inserted in the middle of the sequence.
- Exons required to produce a working protein are deleted.
Because cells read the wrong instructions, human liver cells do not produce an active GULO enzyme but a short nonfunctional protein. Thus, we cannot synthesize ascorbic acid.
Why Did We Keep a Broken Mutation?
More than 60 million years ago, our ancestors lived in the warm climate of tropical lands, eating a diet rich in fresh fruits and vegetables. The abundance of vitamin C in the diet probably made it unnecessary to have a working GULO gene.
The mutation was retained through random genetic drift. The loss of the functional GULO gene allowed saving energy on unneeded biosynthesis of ascorbic acid and decreasing the production of toxic by-products of the reaction, such as hydrogen peroxide (H₂O₂) in the liver.
Convergent Evolution: Other Species in the Same Biological Boat
Humans are not the only species that have lost the ability to produce vitamin C internally. Due to convergent evolution, numerous other species have lost the ability to do so through unique mutations in the GULO gene.
All the haplorhine primates, guinea pigs, capybaras, fruit bats, several songbirds, and most teleost fish are known to have lost their endogenous vitamin C production in the past. The ability to do so was rendered useless due to high concentrations of ascorbic acid in their diets, which caused the genes responsible to stop functioning.
The Critical Biochemical Roles of Vitamin C in the Human Body
Since vitamin C is a water-soluble vitamin, it cannot be stored in the body; therefore, it needs to be replenished frequently.
- Collagen Hydroxylation: It is significant for the activities of Fe²+ which helps maintain collagen cross-linking and ensure the normal function of blood vessels, joints, and skin.
- Antioxidant: It plays an essential role in eliminating free radicals and reducing the oxidative damage caused by them. On the other hand, vitamin C helps regenerate Vitamin E.
- Metabolic & Neural Health: It participates in the formation of neurotransmitters, such as norepinephrine, carnitine, and peptide hormones.
Identifying Subclinical Vitamin C Deficiency
Early Signs of Deficiency in Vitamin C:
- Fatigue, Weakness: Poor conversion of carnitine, decreased production of catecholamines.
- Easy bruising, fragile capillary walls: Diminished collagen production causes the capillaries to rupture easily.
- Bleeding gums: The gums are collagen-rich tissues; therefore, they may bleed easily during vitamin C deficiency.
- Poor healing of wounds: Wounds take a longer time to heal than usual due to disruption in the normal process of tissue repair.
- Strawberry skin: Bumps on the skin surface are formed due to faulty collagen production, thus forming bumps on the skin surface.
- Infections: Infections develop easily due to the malfunctioning of white blood cells.
Optimizing Your Vitamin C Intake
In order to maintain systemic health, tissue repair, and immune resiliency, it is critical to ensure optimal vitamin C levels, rather than just meeting the minimum baseline to prevent scurvy.
Top Whole-Food Sources of Vitamin C
While many are aware that citrus fruits are high in vitamin C, other vegetables and non-citrus fruits can contain even higher concentrations of this vital nutrient, including:
- Kakadu Plums & Camu Camu: 2000-3000 mg per 100g
- Acerola Cherries: 1600 mg per 100g
- Bell Peppers (Yellow/Red): 180 mg per cup
- Guavas: 125 mg per fruit
- Kiwifruit: 70-90 mg per fruit
- Broccoli & Brussels Sprouts: 80-90 mg per cooked cup
- Citrus Fruits (Oranges, Grapefruits): 50-70 mg per medium fruit
The Micronutrient Optimization Protocols at the AAI Rejuvenation Clinic
Since orally administered vitamin C is subject to limited absorption via intestinal sodium-dependent vitamin C symporters (SVCT1), achieving higher systemic concentrations often requires alternative approaches. Our medical team at AAI Rejuvenation Clinic takes a comprehensive approach to micronutrient optimization, considering the patient’s overall nutritional status.
We offer various treatments, including:
- Thorough Laboratory Testing – to assess micronutrient levels and biomarkers of endogenous production
- Liposomal and Oral Micronutrient Supplementation – to ensure optimal intestinal tract utilization
- Vitamin C Infusions – which allow reaching higher concentrations of the vitamin in the bloodstream, surpassing oral tolerance thresholds
- Personalized Approach to Rejuvenation and Micronutrient Optimization- which considers genetic, hormonal, and other individual factors.
Final Thoughts
An ancient genetic mutation deprived the human body of the ability to synthesize vitamin C, making us reliant on dietary sources. Schedule a visit with the AAI Rejuvenation Clinic to assess your current levels and explore treatments that will help your body get the most out of its nutrients.
Medical References
“Gulonolactone (L-) Oxidase, Pseudogene” – NCBI Gene
https://www.ncbi.nlm.nih.gov/gene/2989
https://www.ncbi.nlm.nih.gov/gene/2989
“Vitamin C” – Linus Pauling Institute at Oregon State University
https://lpi.oregonstate.edu/mic/vitamins/vitamin-C
https://lpi.oregonstate.edu/mic/vitamins/vitamin-C
“The Nutrition Source: Vitamin C” – Harvard T.H. Chan School of Public Health
https://nutritionsource.hsph.harvard.edu/vitamin-c/
FAQ's
Our GULO gene on Chromosome 8 was mutated and is nonfunctional. This prevents the liver from producing L-gulonolactone oxidase, an essential enzyme in the conversion of glucose to ascorbic acid.
Other animals that lack the GULO gene and cannot produce vitamin C are: Guinea pigs, capybaras, fruit bats, select bird species, and most teleost fish.
An average adult needs between 75-90 mg of vitamin C per day to avoid deficiency. Maintenance and maximum benefit levels are closer to 500- 1000 mg daily according to the functional medicine and nutritional therapy communities.
The main cause of deficiency is lack of consumption of fresh produce in the diet. Smoking, stress, alcohol consumption, and digestive issues accelerate the depletion of vitamin C in the body, increasing the RDA.
Oral vitamin C has low intestinal absorption, while IV administration delivers 100% of the nutrient directly into the bloodstream, circumventing the digestive system. This allows for extremely high-dose vitamin C therapy, which is used systemically in cancer treatment.
