Vitamin C

A Closer Look at Vitamin C

Vitamin C is a crucial water-soluble vitamin that your body needs in order to maintain your immune system, heal and repair body tissues and wounds, and synthesize crucial neurotransmitters, such as dopamine. Some evidence suggests that vitamin C can also reduce the risk of certain cancers and heart disease. As your body cannot synthesize vitamin C, and vitamin C cannot be stored in fat cells, you need to consume vitamin C daily.

Fortunately, it’s fairly easy to get the vitamin C that you need and vitamin C deficiency is very uncommon. Just by consuming one orange, you can get the daily amount of vitamin C that you need. Individuals who smoke, are pregnant, or lactating need to consume more vitamin C a day than the recommended amount. While rare, people who are on fad diets or have malabsorption issues caused by chronic illnesses may be at risk for vitamin C deficiency. If left untreated, vitamin C deficiency can lead to scurvy, a disease that will cause muscle and tissue to break down and can even be fatal.  

Why Vitamin C is Crucial for Health

Vitamin C is an important antioxidant that can plays an important part in maintaining the immune system, healing and repairing body tissues and wounds, and maintaining bones and teeth. Vitamin C is necessary to produce L-carnitine and collagen, an important protein used in wound healing and making skin, cartilage, tendons, ligaments, and blood vessels. Vitamin C is also crucial for synthesizing dopamine, norepinephrine, epinephrine, and carnitine, which are neurotransmitters needed for energy production.

As an antioxidant, vitamin C can block some of the damage caused by free radicals, which can damage DNA and develop health conditions, such as cancer, heart disease, and arthritis. Vitamin C has been shown to reduce vascular smooth-muscle-cell death, which can in turn prevent atherosclerosis, a hardening and narrowing of the arteries. Vitamin C can regenerate other antioxidants in the body, such as vitamin E and can also help absorb non-heme iron, which is why anemia can be a symptom of vitamin C deficiency.

Some research also shows that vitamin C can play a part in preventing certain cancers as well as reducing the risk of cardiovascular disease. One study shows that 205 mg/day of vitamin C from food compared with an average of 70 mg/day was associated with a 63 percent of lower risk of breast cancer among premenopausal women with a family history of breast cancer. In another study, adults that were in the top quartile of vitamin C concentrations had a 42% lower risk of stroke. Other studies did not prove a correlation between vitamin C intake and a reduction in cancer risk or cardiovascular risk, but one meta-analysis of 14 cohort studies, concluded that dietary, but not supplemental, intake of vitamin C is inversely associated with coronary heart disease risk.  However, that association could be due to the fact that Vitamin C status is one of the best markers for fruit and vegetable intake and consuming fruits and vegetables has been shown to protect against various diseases.

There is also some evidence that suggests vitamin C can help delay age-related macular degeneration (AMD). Additionally, one study showed a correlation between vitamin C intake and a reduction in the development of cataracts in adults. Many people take vitamin C when they have a cold, but studies that investigated whether vitamin C can reduce the symptoms of a common cold have been mixed. One review of dozens of studies concluded that taking 1 g of vitamin C reduced the duration of a common cold by about 8 percent in adults, but did find vitamin C could ward off colds by about 50 percent for those who had been under intense physical stress, such as marathon runners, skiers and soldiers. One study suggests that the reason for this variance in the studies is due to the dosage, suggesting that very high doses of vitamin C at 6-8 g per day rather than the typical 1 g per day, starting when cold symptoms first appear, can reduce the duration of a cold significantly. As vitamin C is cheap and safe, the authors concluded that it may be worth to experiment with high doses when symptoms first begin to appear.

Internal Processing of Vitamin C

Our bodies do not have the ability to synthesize vitamin C and therefore must consume the vitamin daily. Water soluble vitamins, such as vitamin C, are absorbed along with water in the small intestine and then circulate through the blood. As much of the body consists of water, Vitamin C can circulate easily throughout the body.

Our bodies, specifically the kidneys, tightly regulate the amount of vitamin C available at a given time, absorbing 70%-90% of vitamin C at intakes of 30–180 mg/day, but absorbing less than 50% at doses over 1 g/day. Vitamin C cannot be stored in fat cells and excess vitamin C is excreted in the urine. Adults need about 75-90 mg of vitamin C a day and pregnant and lactating women need roughly 85 mg and 120 mg per day. Smokers need about 35 mg more of vitamin C as well.


Just by consuming one or two servings of fruits and vegetables, you can satisfy your vitamin C needs for the day, which is why vitamin C deficiency is extremely rare in developed countries. If left untreated, vitamin C deficiency can lead to scurvy, a condition that occurs when the body is unable to produce enough collagen, causing muscle tissue to break down. Symptoms of vitamin C deficiency can start to appear after only 8 weeks, and can include loss of appetite, weight loss, fatigue, irritability,  lethargy, anemia, myalgia, gum disease, loss of teeth, poor wound healing, shortness of breath, generalized edema, severe jaundice, destruction of red blood cells, known as hemolysis, and even fever and convulsions. Vitamin C deficiency in pregnancy can cause problems with fetal brain development.

Low vitamin C intake can also cause iron deficiency anemia due to increased bleeding and decreased nonheme iron absorption. Scurvy can be fatal if left untreated, but deficiency symptoms occur only if vitamin C intake falls below approximately 10 mg/day for many weeks. Those who are at risk for vitamin C deficiency are smokers, alcoholics, drug addicts, those on very restrictive diets, or those with malabsorption and certain chronic diseases, such as cachexia or chronic hemodialysis.

Most people have enough vitamin C stores to last about a couple of days. The amount of vitamin C content in our bodies ranges from 300 mg, which is very low and near the amount that constitutes scurvy, and 4 grams. Millimolar concentrations, the very high levels of vitamin C, are maintained in cells and tissues. White blood cells, eyes, adrenal glands, pituitary gland, and brain store the highest levels of vitamin C while extracellular fluids, such as plasma and red blood, store the lowest levels.

Lab tests can be used to assess the level of vitamin C in your blood. Vitamin C deficiency can be treated with vitamin C supplements with a recommended dosage of 1- 2 grams g per day for 2-3 days, 500 mg for the next 7 days, and 100 mg for 1-3 months.

Sources of Vitamin C

Raw fruits and vegetables are excellent sources of vitamin C. Around 90% of vitamin C in the human diet comes from fruit and vegetables, but cooking fruit and vegetables reduces their vitamin C content by around 30-40%. Just ½ cup of red pepper has 95 mg of vitamin C and one orange has 70 mg. Other sources include watermelon, papaya, grapefruit, cantaloupe, strawberries, kiwi, mango, broccoli, tomatoes, potatoes, winter squash, raspberries, blueberries, cranberries, and pineapple.


Unless a person is deficient in vitamin C, he or she is likely not to see much benefit from taking vitamin C supplements. In fact, one of the reasons why there is so much variance when it comes to studies involving vitamin C is that if the vitamin C levels of subjects were already close to saturation at the beginning of the study, then vitamin C supplementation would likely have made little or no difference on the outcome. As most people consume enough vitamin C through their diet and excess vitamin C is excreted through the urine, much of the vitamin C in a supplement would likely end up down the drain. Additionally, many of the studies that suggest the benefits of vitamin C point out that these benefits were seen in subjects who consumed vitamin C through food rather than through supplements.

However, although it may not help, it will probably not hurt to take a vitamin C supplement as the upper limit for vitamin C is 2000 mg. Supplements usually use vitamin C in the form of ascorbic acid, which is similar in bioavailability to that of ascorbic acid found naturally in foods, such as oranges. Supplements can use other forms, including sodium ascorbate, calcium ascorbate, mineral ascorbates, and ascorbic acid with bioflavonoids.

One study found no differences in plasma levels or urinary excretion of vitamin C among the  different forms found in supplements, which caused the authors to authors to conclude that simple ascorbic acid, given its low cost, is the best form of of vitamin C for those in supplements. Another review found of multiple studies concluded that there was so difference in bioavailability between vitamin C derived from food and vitamin C derived from supplements. However, the study mentioned that more studies needed to be conducted to fully understand the physiological relevance of bioflavonoids, the compounds found in fruit, and vitamin C.

Two forms of vitamin C supplement called Ester-C and PureWay-C include small traces of vitamin C metabolites, which are substances that play a crucial role in our metabolism. The manufacturers of these products claim that these metabolites, especially lipid and threonate metabolites, increase the bioavailability of the vitamin C, which they proved in a non peer-reviewed study, but these results have not been confirmed. Another study, found no difference in bioavailability between Ester-C and other forms.   

While there doesn’t seem to be much difference in the the various forms of vitamin C, one type of form, called sodium ascorbate, generally contains 111 mg of sodium per dose. So individuals who are are following low-sodium diets may want to be cautious of consuming this form.

Proper Dosage and Contraindications

Adults need about 75-90 mg of vitamin C a day and pregnant and lactating women need roughly 85 mg and 120 mg per day, and smokers should aim to get about 130 mg as well. As most vitamin C supplements have way more than this amount, one should be cautious about over-consuming vitamin C. Even though the maximum daily limit of vitamin C is 1000 mg, vitamin C has low toxicity and there is no conclusive evidence that over-consumption of vitamin C can have any negative consequences.  Some individuals who took vitamin C at high doses, such as more than 2,000 mg daily, reported diarrhea, gas, and/or stomach upset.

Additionally, some studies suggest that vitamin C can potentially act as a pro-oxidant, contributing to oxidative damage. Therefore, some studies suggest supplemental oral vitamin C could cause chromosomal and/or DNA damage and possibly contribute to the development of cancer, but the evidence is not conclusive.

If you have a real vitamin C deficiency, then you should consult your doctor, but generally the recommended dosages of vitamin C supplements to treat a deficiency are 1 to 2 grams (g) per day for 2 to 3 days, 500 milligrams (mg) for the next 7 days, and 100 mg for 1 to 3 months afterwards.

As Vitamin C supplements can cause the body to lose excess fluid, one should make sure to drink plenty of water when taking supplements. Additionally, as vitamin C increases the amount of iron absorbed from foods, individuals with hemochromatosis and thalassemia should avoid vitamin C supplements.

Individuals with kidney problems, a history of kidney stones, sickle cell anemia, as well as those with a metabolic disorder called G6PD, could potentially have serious side-effects from vitamin C supplements. Vitamin C supplements may also raise blood sugar levels in individuals with diabetes, which could in turn increased the risk of death from heart disease. Additionally, individuals, who take birth control or hormone replacement therapy (HRT) should know that vitamin C supplements can cause a rise in estrogen levels when taken in combination with these drugs.

Lastly, if you take aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen (Tylenol), aluminum-containing antacids (Maalox and Gaviscon), barbiturates, such as phenobarbital (Luminal), pentobarbital (Nembutal), and seconobarbital (Seconal), chemotherapy drugs,Tetracycline, minocycline (Minocin) and doxycycline (Vibramycin), Warfarin (Coumadin), or protease inhibitors, you should consult with your doctor before consuming vitamin C as these drugs could have negative reactions with large doses of vitamin C.