Of all the nutrients, vitamin C is one of the most well-known, mostly for its ability to help stave off colds. However, Vitamin C exerts various other important functions as well.
Plus, you might be surprised to learn that oranges are not the highest source of this vital nutrient… (Find out the best vitamin C food sources below!)
Keep reading to discover everything you need to know about this nutrient including the best sources of vitamin C.
What is Vitamin C?
Also called L-ascorbic acid, vitamin C is a water-soluble vitamin, meaning that it dissolves in water and is not easily stored in the body like fat-soluble vitamins A, D, E and K. Thus, extra vitamin C is excreted via urine.
Unlike animals, humans do not endogenously produce vitamin C, so it must be obtained through food or supplementation.
Best Sources of Vitamin C
Generally speaking, fruits and vegetables are the best and most concentrated sources of vitamin C. In addition, some grains like cereal and granola are fortified with vitamin C, but it tends to be less bioavailable.
Nonetheless, consuming five servings of different fruits and vegetables typically earns someone enough vitamin C for the entire day.
Note that because vitamin C is water-soluble, it can be altered in the presence of heat (aka many cooking methods). Luckily, most people consume high vitamin C foods raw. But if cooking the following foods, steaming or microwaving rather than baking or roasting may lessen the nutrient losses caused by heat.
Highest Vitamin C Foods
• Red pepper
• Oranges and orange juice
• Green pepper
• Brussel sprouts
• Tomato juice and tomatoes
• Green Peas
Recommended Daily Intake
In large part thanks to a condition called Scurvy (which you will learn about below), the recommended daily allowance (RDA) or intake for vitamin C is well established. It is based upon its physiological and antioxidant functions in white blood cells and is much higher than the recommended amount for protection against vitamin C deficiency.
Moreover, smokers require higher amounts of Vitamin C – about 35 grams – compared to the general population due to increased oxidative stress from smoke inhalation.
The table below breaks down vitamin C recommendations by gender and life stages, particularly in milligrams (mg).
*Smokers should add 35 mg to these recommendations
Vitamin C Deficiency
The effects of vitamin C deficiency were discovered during the mid-1700s when sailors conducted experiments and determined that eating citrus fruits and juices could cure the symptoms of this deficiency. However, no one yet knew ascorbic acid was the responsible savior.
Acute vitamin C deficiency leads to a condition called scurvy, which begins to manifest after a month or so of little to no vitamin C intake. Initial vitamin C deficiency symptoms include:
• Inflammation of the gums
• Generally feeling bad
As the condition progresses, symptoms become related to weakened connective tissues and include:
• Petechiae- small red/purple dots on the skin that imply improper blood clotting
• Ecchymoses- bruising easily
• Purpura- bursted blood vessels
• Joint pain
• Impaired wound healing
• Hyperkeratosis- thickened, rough skin
• Corkscrew hairs
• Swollen, bleeding gums, and loss of teeth
• Iron deficiency related to increased loss of blood and decreased absorption
While vitamin C deficiency is rare in developed countries, certain populations are at higher risk such as:
• Smokers because of the increased oxidative damage
• Infants fed evaporated or boiled milk because of cow milk’s low vitamin C content and because heat destroys ascorbic acid
• Those with intestinal and malabsorption conditions.
Vitamin C Toxicity
Even though vitamin C is a water-soluble nutrient, it still possesses a tolerable upper intake level of 2000 mg because megadosing this vitamin is associated with diarrhea, other gastrointestinal distress, and kidney stones.
Our intestines have a limited ability to absorb vitamin C, especially when intake is adequate. It is quite a paradox, but studies show that absorption is reduced to less than 50% when consuming amounts greater than 1000 mg of vitamin C. Thus, this is a case of ‘more is not always better.’
Furthermore, while excessive vitamin C does not necessarily produce overt toxic effects in the body, very high doses can shift this nutrient from an antioxidant to a prooxidant, which damages cells.
Vitamin C Supplementation and Medication Interactions
Vitamin C is certainly one of the most supplemented nutrients because of its strong association with mitigating sicknesses like the common cold.
However, as was just discussed, it might not be prudent to take too high doses of supplemental vitamin C. As will be discussed, supplementation of this nutrient is less effective than obtaining it from whole, real foods like bell peppers and citrus fruits.
Nonetheless, the best vitamin C supplements should contain the form of ascorbic acid because it is most absorbable. Other forms like sodium ascorbate, calcium ascorbate, and other mineral ascorbates appear less effective.
Furthermore, vitamin C supplementation can interfere with certain medications or treatments by increasing or decreasing the absorption of other nutrients. Studies show it can lead to higher reabsorption of aluminum and increase estrogen from birth control. It may also reduce the effects of chemotherapy, protease inhibitors, statins, niacin, and warfarin.
On the other hand, vitamin C beneficially increases the absorption of non-heme iron, which can be a beneficial nutritional technique for vegetarians and vegans.
Despite the common belief supplementing with extra vitamin C will kill that pesky influenza, this is not foolproof especially if the intake of whole food sources is already adequate.
Overall, a healthcare provider can help guide you to find the best form of vitamin C and ascorbic acid as needed. Whether a vitamin C powder or chewable tablets, they can also help ensure the product is high-quality without additives like added sugar.
Health Claims About Vitamin C
Vitamin C is undoubtedly beneficial for health in countless ways. Below dives deeper into the true benefits and claims of how the vitamin might benefit the body.
Antioxidant and Immune Function
The main reason vitamin C improves immune function is related to its role as a potent antioxidant. While vitamin E still reigns supreme in this category, vitamin C can also neutralize free radicals which prevent excessive oxidation of cells.
Not only does this inherently enhance immunity, but vitamin C is also needed to produce collagen, a fibrous connective tissue protein that weaves throughout the immune system and other systems like bone, cartilage, blood, and nervous. This also means vitamin C is helpful in promoting healthy, glowing skin!
Moreover, this vitamin serves as a precursor for numerous hormones and neurotransmitters involved with the immune system, nerves, and brain.
Because free radicals and oxidative damage play a major role in the onset and proliferation of cancerous cells, it makes sense that vitamin C may reduce the risk for cancer.
Research shows that vitamin C can limit the formation of carcinogens and modulate proper immune responses. In fact, many studies reveal that higher consumption of fruits and vegetables is associated with reduced cancer risk, likely related to their high vitamin C content.
Specifically, research shows that adequate intake of vitamin C is associated with a reduced risk of cancers such as breast, colon, esophageal, lung, and oral types.
However, only vitamin C intake from real foods revealed this association. In fact, modest supplementation of isolated vitamin C or in conjunction with other supplemental nutrients revealed little benefit.
Once again, this highlights that real foods likely possess other beneficial compounds that work synergistically to exert their full power.
It’s well known that higher consumption of fruits and vegetables correlates with a lower risk of cardiovascular disease and related complications like high blood pressure or cholesterol. These plant foods’ high antioxidant activity is partly responsible for reducing oxidative damage of tissues associated with heart disease, but vitamin C specifically exerts benefits.
Acting as an antioxidant, vitamin C:
• Improves nitric oxide production and vasodilation to regulate blood pressure
• Reduces heart tissue death
• Helps prevent the build-up of plaque associated with heart attacks and chronic heart failure
Once again, these benefits were not observed when vitamin C supplementation served as the main source of intake. Whole foods for the win (again)!
Age-Related Macular Degeneration
Finally, because oxidative damage is highly implicated in the development of cataracts and age-related macular degeneration (AMD), it’s plausible that vitamin C may help prevent this.
Indeed, studies show that those with high intakes of vitamin C along with beta-carotene [LINK TO VITAMIN A article], vitamin E, and zinc reduced the risk of AMD and cataracts.
Adequate blood concentrations of vitamin C may help prevent the development of this eye disease, but as has been mentioned, supplementing with vitamin C after the onset of AMD did not affect its progression. Thus, vitamin C may be protective but likely can’t treat or reverse this condition.
The Bottom Line On Vitamin C
From supporting eye health to bolstering immune function, vitamin C is highly beneficial to health.
Fruits and veggies are rich sources of vitamin C, as well as some whole grains and other products that have been fortified with the vitamin. Consuming an average of five servings of colorful produce is likely to cover your vitamin C bases.
While whole foods trump supplementation, they might be considered and recommended as needed. Always consult with your primary care provider or healthcare team to determine if supplementing is right for you and your individual needs.
Vitamin C. NIH Office of Dietary Supplement. Updated March 26, 2021. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/.
Vitamin C. Harvard Health. Updated March 2020. https://www.hsph.harvard.edu/nutritionsource/vitamin-c/.
Mayo Clinic Staff. Vitamin C. Mayo Clinic. Published November 17, 2020. https://www.mayoclinic.org/drugs-supplements-vitamin-c/art-20363932.