Think you know all you need to know about vitamin C? Think again.
Over the last five years there have been some exciting developments in the emerging science of Vitamin C that go far beyond its traditional reputation as an immune booster. Vitamin C is finally being recognized for its amazing versatility as a powerhouse in human resilience and combating the ravages of aging and disease. From its role in fighting COVID-19 and treating Long COVID to its emerging role in supporting heart, brain, and metabolic health, we are going to explore some of the latest research, review its multiple roles in the body, and discuss smart supplementation strategies to optimize the benefits of taking vitamin C.
For more than 30 years, I personally have taken naturally derived vitamin C with citrus bioflavonoids twice a day, in the morning and every evening. I have also included vitamin C in my recommendations for my patients since I began practicing medicine. Vitamin C is a water-soluble vitamin that is essential to human health because we are one of the few mammals that cannot synthesize it and must get it from our diet or supplements. Vitamin C is the primary active ingredient in citrus fruits that has long been known to prevent scurvy – remember the nickname “Limey” for the British Navy in the 1700s? That term originated from the Royal Navy’s practice, initiated in 1795, of issuing lime juice to sailors to prevent scurvy. Although lemon juice was initially used, the Navy switched to limes in the early 1800s due to their availability in British colonies, particularly in the Caribbean. Sailors eating limes on long voyages were found to have better health than those whose diet was just the typical salted meat.
Since the 1970s, studies have shown that supplementing vitamin C significantly reduces missed days from work/activities and reduces length of illness. Vitamin C has long been valued for supporting immune health. It boosts white blood cell function, enhances pathogen clearance, and reduces the length and severity of common colds and other respiratory illnesses. Scurvy, the severe disease from vitamin C deficiency, is rare today, but our need for vitamin C has markedly increased due to other modern lifestyle factors: stress, pollution, smoking, illness, environmental factors like chemicals, endocrine disrupters, and temperature changes, as well as the immune and vascular damage from modern medical interventions such as the COVID jab.
VITAMIN C INFLUENCES THE HEALTH OF EVERY TISSUE IN THE BODY! Redefining Vitamin C: New Science in COVID-19 and Chronic Diseases
Vitamin C is vital in many functions throughout the body and also shows great promise in expanded roles as a redox- and endothelium modulating agent in acute COVID, Long COVID, COVID vaccin injury, and several chronic cardiometabolic and neurodegenerative conditions. Some of the many functions that are Vitamin C dependent include:
- Collagen formation (bones, skin, blood vessels, gums, joints)
- Immune defense
- Antioxidant protection against free radicals
- Energy production (through carnitine synthesis)
- Mood and brain function (neurotransmitter synthesis)
Acute COVID-19 Redox Modulation and Endothelial Protection:
Recent trials have been focused on high-dose intravenous vitamin C as an adjunct treatment in hospitalized COVID-19 patients. Some of the key benefits include:
- Regulating oxidative stress and reducing “cytokine storm”
- Protecting the endothelial barrier, which helps prevent dangerous fluid leakage and organ failure
- Supporting immune cell balance and reducing inflammation
- Enhancing oxygenation and shortening ICU stays in select cases
My professional opinion is that the key point here is to administer vitamin C early as soon as symptoms or diagnosis is made. I have recommended its use as a supplement in my early COVID-19 at home treatment protocols, and in my approaches to treating COVID vaccine injuries as well.
Long COVID/COVID VAX INJURY: Combating Fatigue and Vascular Dysfunction
Long COVID and COVID Vaccine injury are increasingly framed as damages due to endothelial and redox dysfunction, leading to persistent endothelial damage that decreases optimal blood flow with oxygen and nutrients –which in turn leads to silent hypoxia and fatigue. Research shows that combining vitamin C with L-arginine (an amino acid that boosts nitric oxide production) for 28 days significantly improved vascular health, reduced fatigue, and enhanced physical performance in affected adults. It was this synergy that appears to be so beneficial in restoring endothelial function and reducing oxidative stress, two of the key mechanisms in post-COVID recovery. Another interesting finding is that vitamin C deficiency and increased oxidative stress markers have been reported in groups being studied after having COVID-19 and may signal another clue to contributors of Long COVID, and I also see this in my patients with COVID vaccine injuries and similar symptoms, even if they did not have COVID illness.
Cardiometabolic Conditions:
Vitamin C’s benefits extend to cardiovascular and metabolic diseases: Vitamin C improves endothelial function, lowers blood pressure, and reduces vascular inflammation.
- Vitamin C improves endothelial function primarily by scavenging reactive oxygen species (ROS), preserving nitric oxide (NO) bioavailability, and stabilizing the endothelial barrier against inflammatory damage. It enhances endothelial nitric oxide synthase (eNOS) activity, boosts NO-dependent vasodilation (measured as flow-mediated dilation or FMD), and prevents oxidative degradation of NO, which otherwise impairs vessel relaxation. These effects restore vascular reactivity during inflammation or oxidative stress, as seen in trials where acute or oral vitamin C normalized flow-mediated dilation in older adults and heart failure patients.
- Vitamin C lowers blood pressure, particularly in hypertensive individuals, by improving endothelial NO production and reducing vascular stiffness. Meta-analyses show supplementation (median 500 mg/day) reduces systolic BP by 3.8-4.9 mm Hg and diastolic BP by 1.5-1.7 mm Hg, with greater effects in those with baseline hypertension. This occurs through antioxidant protection of NO and cAMP signaling, which maintains vessel tone without altering heart rate or pulse wave velocity in short-term studies.
- Vitamin C reduces vascular inflammation by neutralizing ROS, inhibiting pro-inflammatory cytokines, and limiting endothelial permeability to leukocytes. It preserves cAMP levels to block stress fiber formation and barrier breakdown induced by thrombin or inflammation, while sparing NO to counter oxidative damage in conditions like sepsis or atherosclerosis. In cardiovascular disease, these actions attenuate systemic inflammation markers and endothelial injury without directly altering acute-phase proteins like CRP or IL-6.
Metabolic disease:
Overall, Vitamin C supports pancreatic beta-cell function, improves glucose control, and modulates inflammation in diabetes and metabolic syndrome (Pre-diabetes).
- Vitamin C improves metabolic health through its antioxidant actions that reduce oxidative stress, enhance insulin sensitivity, lower lipid levels, and decrease inflammation in conditions like metabolic syndrome and type 2 diabetes.
- Higher dietary or plasma vitamin C levels correlate with reduced risk of metabolic syndrome (RR 0.93 for highest vs. lowest intake), lower BMI, waist circumference, fasting glucose, insulin resistance (HOMA-IR), triglycerides, and LDL cholesterol, while raising HDL. Supplementation (e.g., 4 weeks) in animal models and humans further supports this by scavenging free radicals, improving neutrophil function to clear adipose inflammation, and synergizing with exercise to amplify benefits on weight, blood pressure, and dyslipidemia.
Vitamin C’s protective roles in key metabolic pathways
- Pancreatic beta-cell function: Vitamin C acts as a cofactor for enzymes in insulin synthesis and protects beta cells from oxidative damage and glucotoxicity, preserving their ability to secrete insulin under high-glucose stress.
- Glucose control: By reducing ROS-mediated insulin resistance and enhancing glucose uptake, vitamin C supplementation lowers fasting blood glucose, HbA1c, and postprandial spikes, with inverse associations seen in cohort studies.
- Inflammation modulation: Vitamin C inhibits pro-inflammatory cytokines in adipose and vascular tissues, improves neutrophil chemotaxis for inflammation resolution, and prevents lipid peroxidation, addressing chronic low-grade inflammation central to diabetes and Metabolic syndrome.
Neurodegenerative Conditions:
Vitamin C supports neuroprotection and cognition through its actions as a cofactor in neurotransmitter synthesis and may lower risk for Alzheimer’s and other neurodegenerative diseases.
- Vitamin C neuroprotective actions are mainly through its potent antioxidant activity, scavenging reactive oxygen species (ROS) in the brain, reducing oxidative stress, and activating pathways like Nrf2/HO-1 to boost endogenous defenses such as SOD while lowering lipid peroxidation (MDA).
- Vitamin C crosses the blood-brain barrier via SVCT2 transporters, accumulating in neurons and glia to inhibit β-amyloid aggregation, protect against Blood-brain barrier disruption, and mitigate inflammation from cytokines like TNF-α and IL-6.
- These actions preserve neuronal integrity in models of sepsis, stroke, and neurodegeneration, including amyloid plaque buildup.
- Cofactor in neurotransmitter synthesis: Vitamin C serves as an essential cofactor for dopamine-β-hydroxylase, converting dopamine to norepinephrine, which supports catecholamine balance and prefrontal cortex functions like executive control.
- Supports cognition: By reducing neuroinflammation, oxidative damage, and hippocampal pathology, supplementation improves memory, learning, and spatial recognition in animal models and correlates with better cognitive scores in older adults.
- Lowers risk for Alzheimer’s and other neurodegenerative diseases: Higher vitamin C intake links to reduced dementia risk via ROS scavenging, Aβ inhibition, endothelial/collagen support for cerebral vessels, and epigenetic modulation (e.g., TET activation for 5hmC in neuroprotective genes).
Vitamin C and Flavonoids: A Synergistic Combo to Enhance Benefits!
Supplements that combine vitamin C with bioflavonoids (plant compounds found in citrus and colorful fruits) offer enhanced benefits for heart, immune, connective tissue, vascular and brain health:
- Stronger antioxidant and anti-inflammatory effects
- Improved cardiovascular markers, such as platelet reactivity and vascular health
- Greater stability and bioavailability of vitamin C
- Improved collagen and connective tissue formation to enhance wound healing
- Positive impacts on immune system and microbial balance
This is why I don’t recommend just any typical vitamin C product as part of a regular supplement regimen. I have always used, and recommended a naturally derived Vitamin C with bioflavonoids. For our Truth for Health Foundation store, we have selected a particularly high quality and unique formulation: TruC+BioFlav™
Our TruC+BioFlav™ is a unique combination of high-potency vitamin C with a standardized, full-spectrum citrus bioflavonoid complex in a 1:1 ratio. This is important because these two are found together in nature, and benefits are significantly enhanced with they are combined as nature intended.
Bioflavonoids are phytochemicals, pigments that give fruits and flowers their colors and are usually found together with vitamin C in nature. More than 4000 bioflavonoids have been identified, and they are considered to be among the most important and interesting classes of biologically active compounds in contemporary research. Intake of flavonoids is associated with healthy cardiovascular status, the body’s normal response to inflammation, and positive microbial balance.
Bioflavonoids are used in clinical protocols to support tissue and joint comfort and the body’s normal response to inflammation, respiratory and eye health, and maintenance of cardiovascular health. Citrus bioflavonoids are able to cross the blood-brain barrier and have been recognized for their neuroprotective effects.
As cell-signaling agents, bioflavonoids+ are believed to support healthy cell growth and normal cell-life regulation (important in cancer prevention), they stimulate detoxification enzymes, decrease vascular cell adhesion molecules (think blood clots and cardiovascular disease prevention), increase vasodilation (good for blood pressure), and support healthy platelet function.
TruC+BioFlav™ is truly a work horse when it comes to improving health and resilience and defending ourselves from stress and environmental or infectious threats to our health. That’s why we have included TruC+BioFlav™ as an essential component of our TruResilience Formula. You may purchase it separately to help you reduce risk of illness during cold and flu season or as part of our Resilience Formula for multiple health benefits and additional discounts.
Optimal intake of vitamin C for humans continues to be debated, though normal vitamin C synthesis in mammals such as the rat is calculated to be 26-58 mg/kg/day. Dr. Linus Pauling, in his 1970 article on evolution and vitamin C requirements, recommended a minimum intake of 2300 mg per 2500 kilocalorie intake per day for humans.
For many years I have personally been taking vitamin C with bioflavonoids 2000 mg daily all year around because it has so many benefits to overall health. Then I increase the dose if I get a cold or flu or following surgery to improve wound repair and healing.
Dosing Vitamin C: What Science Says
| Health Condition |
|
Typical Dose/Regimen |
|
Key Notes |
|
| Common Cold |
|
1–2 g/day orally; up to 3–4 g/day at onset |
|
Reduces duration/severity; no strong prevention effect beyond diet |
|
| COVID-19 / ARDS |
|
12–24 g/day IV for 4–7 days (hospitalized) |
|
Adjunctive for severe cases; mixed evidence in large trials |
|
| Cardiovascular Health |
|
500 mg–2 g/day orally |
|
Supports blood pressure, endothelial function |
|
| Autoimmune / Inflammatory |
|
500 mg–2 g/day orally |
|
Reduces inflammation, supports immune modulation |
|
| Metabolic Disease |
|
500 mg–1 g/day orally |
|
Improves glycemic control, antioxidant status |
|
| Neuroprotection |
|
500 mg–2 g/day orally |
|
Supports cognitive and neurotransmitter function |
|
| General Health |
|
500 mg-2 g/day |
|
|
|
Foods Rich in Vitamin C: Suprising Sources Beyond Citrus
When you think about food sources of vitamin C you probably think about oranges and other citrus fruits. Well, you might be surprised that several other fruits and vegetables offer more vitamin C than oranges. Consider expanding your options with these choices:
- Guava (1 cup: >300 mg)
- Papaya, kiwi, black currants, sweet bell peppers (especially red/yellow)
- Mustard greens, kale, broccoli, Brussels sprouts, cabbage, cauliflower
- Hot chili peppers, kohlrabi, tomatoes, arugula, parsley, spinach, bok choy
- Cantaloupe, pineapple
To maximize your vitamin C intake especially from vegetables, make sure to use what I call “light” cooking methods such as steaming, stir-frying as these methods help preserve vitamin C. If you boil your vegetables make sure to use filtered water and retain that water in a glass container for use to make stock or in soups, rice or anything with water. This will keep for a couple of days in the refrigerator.
A Few Cautions with Vitamin C
Some individuals should use caution when supplementing vitamin C and should discuss its use with their physician, although most of these concerns are indicated with high-dose vitamin C supplementation and not at the doses listed earlier and supported by scientific studies.
- Those with blood disorders related to iron metabolism (hemochromatosis, thalassemia, G6PD deficiency)
- Kidney disease or history of stones (risk of oxalate stones)
- Patients undergoing chemotherapy or radiation
- Individuals on medications that interact with vitamin C (aspirin, NSAIDs, tetracycline, corticosteroids, etc.)
- Diabetes patients (may affect glucose readings)
- Pregnant or breastfeeding women (avoid high doses unless advised by a healthcare provider)
- Anyone with a sensitive digestive tract or allergies to vitamin C
Signs You Should Reduce Vitamin C Intake: If you experience any of these symptoms, lower your dose and seek medical advice.
- Diarrhea, nausea, stomach cramps, bloating (often above 2,000 mg/day)
- Kidney stone development or worsening
- Symptoms of iron overload (especially in those with certain blood disorders)
- Potential nutrient imbalances (B12, copper)
- Interference with lab tests (e.g., stool occult blood)
- Rarely, headache or esophageal swelling
In summary, Vitamin C is far more than just a remedy for colds or a shield against scurvy. Over the past five years, research has illuminated its crucial roles in immune defense, vascular health, brain function, chronic disease management, and cellular resilience, especially in the wake of COVID-19. Whether you’re seeking to support your heart, brain, immune system, or recovery from illness, vitamin C deserves a central place in your nutrition and resilience strategies. For most people, a diet rich in fruits and vegetables, supplemented with a high-quality naturally-derived vitamin C with bioflavonoids provides robust support for improved health and resilience.
CAUTION: As always, we urge you to avoid supplements without checking knowledgeable sources to evaluate your medical situation, proper lab tests to verify what is needed, and to make sure to avoid adverse interactions with prescription medicines and other supplements you take.
All Truth for Health Foundation Products Meet or Exceed cGMP Quality Standards, the highest quality standard for supplements sold in the USA. For more information, references from studies are listed in the Product Data Sheets for each product, available on our website. Under medical practice regulations, we are unable to answer individual medical questions or make specific individual supplement recommendations for people who are not established patients of Dr. Vliet’s independent medical practice.
I encourage you to consider our other natural medicines with our top quality, cGMP-compliant professional formulas for TruImmune™Boost, TruNAC™, TruImmunoglobulin,™ Tru BioD3™, TruZinc™, TruMitochondrial ™Boost and TruProBiotic™ Daily to replenish critical bifidobacteria depleted by COVID shots, viral illnesses, and antibiotic therapy.
To Your good health and improving resilience!
Elizabeth Lee Vliet, MD
References and Further Reading
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