When flu season pokes its head around the corner, most people go into overdrive - including supplement manufacturers. With shelves full of all the best immune boosters, they promise to decrease the odds of catching a common cold that's going around.
But while no one immune formula is alike, there's something a lot of them have in common: vitamin C. It's one of the most well-known immune-boosting antioxidants that strengthen immune defenses to help your body fight pathogens.
It's widely available in supplement form, but most people get enough of it through diet. So, when cold and flu season rolls around, mega-dosing supplemental vitamin C to bolster immunity can be tempting, but should you do it?
Right now, we're digging into the details of vitamin C and the undesirable effects that can occur when taken in large doses. We'll look at the benefits of vitamin C, how much you need, and if it's possible to overdose.
Let's dive in.
What is Vitamin C?
Also called ascorbic acid, vitamin C is a water-soluble vitamin noted for its antioxidant and immune-boosting properties.
Because vitamin C isn't stored in the body - we excrete excess in urine - it must be consumed daily through diet or supplementation to ensure intake requirements are met.
Its role in immunity is perhaps its most well-known function, but its importance spans beyond that. Vitamin C also plays a crucial role in:
- Collagen synthesis
- Wound repair
- Bone formation
- Blood vessel health
- Reducing oxidative stress and DNA damage
Because vitamin C is an electron donor - this also makes it a reducing agent - it can donate electrons to unstable molecules to neutralize them and prevent them from causing damage; this property is the basis of most of vitamin C's physiological and biochemical - they make it one of the most powerful 1.
But unlike most other molecules that lose an electron and become unstable and reactive, vitamin C doesn't. It's relatively stable when it gives up an electron, meaning it can continue to scavenge radicals without risking becoming a radical itself.
However, as a water-soluble nutrient, vitamin C must be replenished daily to ensure levels stay up to par. Not enough can lead to compromised antioxidant and immune defenses, but periods of illness or high stress also deplete vitamin C, further increasing requirements 2.
But unlike some nutrients the body can synthesize in small amounts, vitamin C isn't one of them. Some mammals possess the enzymes necessary to produce vitamin C, but humans lack it - gulonolactone oxidase 3. There are only two sources it can come from - food or supplementation.
Vitamin C and Immunity
Because of its powerful antioxidant properties, vitamin C is among some of the best natural immune-boosting compounds. Vitamin C acts as a reducing agent and protects cells against the harmful effects of free radicals and oxidative stress-induced cellular damage 4.
While it may be wise to think that reducing free radical production could be even more effective for mitigating oxidative stress, sometimes that's easier said than done.
Although free radicals are generated from smoking, industrial chemicals, and environmental pollution, they're also a natural byproduct of metabolic processes, including intense exercise 5.
However, the body is naturally equipped with a powerful endogenous antioxidant defense system that combats free radicals. Still, when radical levels exceed the capability of the antioxidant system, oxidative stress levels start to increase.
Long-term, excessive oxidative stress drive diseases; it's been implicated in numerous chronic and degenerative diseases, such as autoimmunity, cancer, premature aging, cataracts, rheumatoid arthritis, cardiovascular disease, and neurodegenerative diseases 6.
On top of that, it's also critical for supporting mucosal barriers that keep pathogenic bacteria out. The epidermal layer that protects the body and serves as a barrier mainly comprises keratinocytes, while the dermal layer comprises fibroblasts that secrete collagen 2.
High vitamin C concentrations are found in the dermis and epidermis, where it actively accumulates and offers protection. In the skin, it's involved in:
- Collagen production and stabilization
- Preventing free radical-induced cellular damage
- Supporting keratinocyte differentiation and lipid synthesis
- Enhancing fibroblast proliferation and movement
- Accelerating wound healing
There are numerous benefits of vitamin C for the immune system, but we're not going to dive into them.
And like we said, bulking up on your vitamin C intake is the typical solution for anyone looking to keep their immune system sharp, but it's not always the best solution - sometimes, slow and steady wins the race.
Other Benefits Of Vitamin C
What else does vitamin C do besides the immune system and antioxidant defenses?
- Reduces the risk of chronic disease: Like we just mentioned, vitamin C's potent antioxidant status is critical for preventing chronic conditions with an underlying inflammatory and oxidative stress component. Studies find that daily vitamin C supplementation can increase blood antioxidant concentrations by up to 30%, which supports your body's ability to curb inflammation 7, 8! It's also a major player in reducing the risk of heart disease. A meta-analysis of nine studies with over 293,172 participants found that after ten years, people who supplemented with at least 700 mg of vitamin C daily reduced their risk of heart disease by a staggering 25% compared to those who didn't take it 9. It may do so by improving blood cholesterol and triglyceride levels.
- May reduce high blood pressure: Between 2017 and 2018, nearly 50% of all Americans had high blood pressure 10. Although minor deviations in blood pressure levels aren't a huge deal, hypertension dramatically increases the risk of heart disease - the leading cause of death worldwide. Although studies aren't conclusive, human and animal studies find that vitamin C can help relax blood vessels that carry blood to the heart, lowering blood pressure 11, 12.
- Prevents iron deficiency: Keeping iron levels up is a must for anyone following a plant-based diet. Non-heme iron derived from plant sources is significantly less bioavailable than heme-iron, which means vegan and vegetarian iron levels tend to suffer. However, vitamin C improves the bioavailability of non-heme iron; enhanced iron absorption from plant-based meals is directly proportional to how much ascorbic acid is present in the meal 13. As such, more vitamin C = more iron absorbed.
How Much Vitamin C Do We Need?
The recommended daily intake for vitamin C is just 75 mg for women and 90 mg for men 5. Hitting the recommended intake is generally feasible for most people through diet, but it could be challenging for anyone who follows a diet devoid of most plant foods.
Curious to know how much vitamin C is in common foods? Here's an idea:
- Freshly squeezed orange juice (1 cup): 96 mg
- Kakadu plums (1 plum): 436 mg
- Rose hips (100 grams): 426 mg
- Bell peppers (1 large): 324 mg
- Blackcurrants (1/2 cup): 102 mg
- Acerola cherries (1/2 cup): 825 mg
- Cantaloupe (1 cup): 17.4 mg
Several other foods also contain vitamin C, albeit in smaller quantities:
- Kiwi
- Parsley
- Spinach
- Kale
- Broccoli
- Brussel sprouts
- Lemons
- Lychee
- Persimmon
- Papaya
- Strawberries
- Orange
Side Effects Of Too Much Vitamin C
As a water-soluble vitamin, excessive vitamin C intake isn't likely harmful, although it can cause some unwelcome side effects. Most symptoms of excessive vitamin C intake are gastrointestinal-related, with the most common being:
- Nausea
- Diarrhea
- Vomiting
- Heartburn
- Abdominal cramps
- Headaches
Long-term supplementation with high doses of vitamin C can also increase the risk of kidney stones in some people, especially those with a history of them 14.
They're usually short-term side effects, but they're not the most pleasant things to experience, so finding the correct (and appropriate) dosage is key.
And while high doses of vitamin C aren't inherently dangerous and "overdosing" is a possibility, we like to think about it more in terms of "overdoing it" rather than overdosing - you still don't want to go overboard. Ideally, it's not recommended to exceed doses of 2,000 mg to avoid unwanted side effects.
So, what's the solution to avoid the nasty side effects of too much vitamin C? Look for a controlled dose! For most people, vitamin C intake from food suffices to meet the requirements.
Still, when you need a little boost - when you're sick or stressed out, for example - Performance Lab NutriGenesis Multi and Performance Lab PL-Immune can provide that boost.
They're state-of-the-art formulas designed to provide your body with precisely what it needs to perform. Using NutriGenesis patented technology, they're also packed with nature-identical vitamins and minerals formulated for maximum absorption and bioactivities. Plus, they're ultra-clean and ultra-effective - no synthetic additives, flavors, or colors.
References
- Padayatty SJ, Katz A, Wang Y, et al. Vitamin C as an antioxidant: evaluation of its role in disease prevention. J Am Coll Nutr. 2003;22(1):18-35.
- Carr AC, Maggini S. Vitamin C and Immune Function.Nutrients. 2017;9(11):1211.
- Ha MN, Graham FL, D'Souza CK, Muller WJ, Igdoura SA, Schellhorn HE. Functional rescue of vitamin C synthesis deficiency in human cells using adenoviral-based expression of murine l-gulono-gamma-lactone oxidase. 2004;83(3):482-492.
- Traber MG, Stevens JF. Vitamins C and E: beneficial effects from a mechanistic perspective. Free Radic Biol Med. 2011;51(5):1000-1013.
- Yimcharoen M, Kittikunnathum S, Suknikorn C, et al. Effects of ascorbic acid supplementation on oxidative stress markers in healthy women following a single bout of exercise. J Int Soc Sports Nutr. 2019;16(1):2.
- Pham-Huy LA, He H, Pham-Huy C. Free radicals, antioxidants in disease and health. Int J Biomed Sci. 2008;4(2):89-96.
- Kim MK, Sasazuki S, Sasaki S, Okubo S, Hayashi M, Tsugane S. Effect of five-year supplementation of vitamin C on serum vitamin C concentration and consumption of vegetables and fruits in middle-aged Japanese: a randomized controlled trial. J Am Coll Nutr. 2003;22(3):208-216.
- Popovic LM, Mitic NR, Miric D, Bisevac B, Miric M, Popovic B. Influence of vitamin C supplementation on oxidative stress and neutrophil inflammatory response in acute and regular exercise. Oxid Med Cell Longev. 2015;2015:295497.
- Knekt P, Ritz J, Pereira MA, et al. Antioxidant vitamins and coronary heart disease risk: a pooled analysis of 9 cohorts. Am J Clin Nutr. 2004;80(6):1508-1520.
- Chobufo MD, Gayam V, Soluny J, et al. Prevalence and control rates of hypertension in the USA: 2017-2018. Int J Cardiol Hypertens. 2020;6:100044.
- Ettarh RR, Odigie IP, Adigun SA. Vitamin C lowers blood pressure and alters vascular responsiveness in salt-induced hypertension. Can J Physiol Pharmacol. 2002;80(12):1199-1202.
- Juraschek SP, Guallar E, Appel LJ, Miller ER 3rd. Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012;95(5):1079-1088.
- Lynch SR, Cook JD. Interaction of vitamin C and iron. Ann N Y Acad Sci. 1980;355:32-44.
- Ferraro PM, Curhan GC, Gambaro G, Taylor EN. Total, Dietary, and Supplemental Vitamin C Intake and Risk of Incident Kidney Stones. Am J Kidney Dis. 2016;67(3):400-407.
