Vitamin C: benefits, side effects, dosage and interactions


Vitamin C, also known as ascorbic acid, is an essential nutrient that keeps the body going. It is found in foods and dietary supplements and aids in many biological functions, including collagen synthesis, wound healing, and the repair and maintenance of cartilage, bones, and teeth. Vitamin C is also an antioxidant, which means it can neutralize free radicals that damage cells at the genetic level .

Historically, vitamin C was used to prevent or treat scurvy and other conditions associated with vitamin C deficiency. Today, it is widely touted as a natural remedy for the common cold. Although vitamin C is considered an "immune booster," there is little evidence that taking it can prevent or cure infection .

Good sources of vitamin C can be found in fruits and vegetables, especially citrus fruits.

What is vitamin C used for?

The only condition that vitamin C can definitely treat is vitamin C deficiency. According to research from the Centers for Disease Control and Prevention (CDC), approximately 7.1% of the US population can be classified as vitamin C deficient. People with severe dietary vitamin C deficiency may develop scurvy, characterized by bruising. , bleeding gums, weakness, fatigue and a rash.

In addition to the known deficiency, some believe that vitamin C helps in the treatment or prevention of a variety of conditions, including colds, asthma, bronchitis, cancer, chronic pain, cataracts, gastritis, glaucoma, heart disease, high blood pressure , osteoarthritis and Parkinson 's disease

While the evidence supporting these claims is generally weak, there have been several promising discoveries in recent years.


The benefits of vitamin C in fighting colds are more speculated than research-based. Supplementation with vitamin C did not appear to have any effect in reducing the incidence of colds in participants compared to the general population, based on a 2007 review of several studies with 11,306 participants .

That said, the authors noted that vitamin C could potentially benefit athletes or people living in extremely cold climates.

A 2013 review in Finland concluded that vitamin C could not prevent colds, but could reduce their course by about 8% in adults and 14% in children with a daily dose of 1,000 to 2,000 milligrams .

Loss of sight

There is some evidence that vitamin C supplementation may slow the progression of macular degeneration associated with aging eye disease characterized by vision loss.

A 2001 study in the Archives of Ophthalmology found that people at high risk for the disease who took 500 milligrams of vitamin C per day along with beta-carotene, vitamin E, and zinc reduced the progression of macular degeneration by 25% and lost the visual acuity. by 25% .15% .

A 2014 review from Tufts University concluded that taking 135 milligrams of vitamin C a day can prevent certain types of cataracts and that doses of at least 363 milligrams can reduce the risk of developing cataracts by at least 57% .

High blood pressure

The benefits of vitamin C in treating hypertension (high blood pressure) have long been touted, although the actual effects are not as strong as previously thought.

According to a 2012 study from Johns Hopkins University, high doses of vitamin C, around 500 milligrams per day, caused only a small decrease in systolic (upper) blood pressure, but had a minimal effect on diastolic blood pressure ( bottom) .

While scientists have yet to establish why this is the case, high doses of vitamin C are believed to have a mild diuretic effect , helping to remove excess fluid from the body. This can help reduce the pressure in the blood vessels.

Heart disease and cancer

Vitamin C is often wrongly praised for its ability to fight heart disease and cancer. Many misconceptions are caused by the antioxidant properties of vitamin C.

While antioxidants appear to reduce oxidative stress associated with these diseases, there is little evidence that vitamin C supplementation can directly affect risk.

Among the clinical findings:

  • A 10-year study of 14,641 men over the age of 50 found that a 500 mg dose of vitamin C had no effect on heart attacks or strokes compared to placebo .
  • A nine-year study involving 8,171 older women found that 500 milligrams of vitamin C did not affect cancer incidence compared to the general population .
  • A five-year study of 77,721 older men and women also showed no association between vitamin C intake and risk of lung cancer .

Possible side effects.

Although vitamin C is generally considered safe, high doses can cause side effects including heartburn, nausea, headaches, stomach cramps, and diarrhea. Doses greater than 2000 milligrams are considered extreme and can increase the risk of severe diarrhea and kidney stones .

Although you can safely take vitamin C during pregnancy, overuse can harm your newborn. Generally speaking, 85 to 120 milligrams per day is considered sufficient for a pregnant woman; others may take more …

Vitamin C can also raise blood sugar levels and should be taken with caution if you have diabetes . In older women with diabetes, more than 300 milligrams of vitamin C per day increases the risk of dying from heart disease .

Drug interactions

Vitamin C can slow down the removal of estrogens from the body. Taking vitamin C with estrogens or estrogen-based birth control can increase your risk of hormonal side effects .

The opposite can happen with the antipsychotic drug Prolixin (fluphenazine). When taken together, vitamin C can reduce the concentration of prolixin in the bloodstream and reduce the effectiveness of the drug. Vitamin C supplements can also reduce the effectiveness of some chemotherapy drugs.

To avoid interactions, tell your doctor if you are taking or plan to take vitamin C with any of these types of medications.

Get Drug Information / Anastasia Tretyak

Dosage and preparation

The RDA for vitamin C for general health is as follows:

  • Children 0 to 6 months: 40 milligrams daily.
  • Children 7 to 12 months: 50 milligrams daily.
  • Children 1 to 3 years: 15 milligrams daily.
  • Children 4 and 8 years old: 25 milligrams daily.
  • Children 9 to 13 years: 45 milligrams daily.
  • Women ages 14 to 18: 65 milligrams daily.
  • Men ages 14 to 18: 75 milligrams daily.
  • Women 19 years and older: 75 milligrams daily.
  • Men older than 19 years: 90 milligrams per day
  • Pregnant women ages 14 to 18: 80 milligrams daily.
  • Pregnant women 19 years of age and older: 85 milligrams per day.
  • Breastfeeding women ages 14 to 18: 115 milligrams daily.
  • Women who breastfeed from the age of 19: 120 milligrams daily .

Smokers should take an additional 35 milligrams per day. Those diagnosed with a vitamin C deficiency should take 100 to 200 milligrams a day until blood levels return to normal.

Vitamin supplements are available in the form of tablets, capsules, chewable tablets, gummies, effervescent powders, and tablets. Despite what some may tell you, vitamin C gum is no more or less effective than a tablet or capsule.

What to look for

Not all vitamin C supplements are the same. To best ensure quality and safety, choose supplements that have been tested and certified by an independent certification body such as USP, ConsumerLab, or NSF International.

It should also be taken into account that there are different types of vitamin C, including L-ascorbic acid (generally obtained from corn) and others that combine ascorbic acid with minerals (such as sodium or calcium), citrus bioflavonoids or rose hips . Neither of these is considered better or more effective than the other for dietary use.

Regardless, you can save money by choosing a "plain" L-ascorbic acid supplement and avoiding all other non-essential supplements. The best way to get vitamin D is through foods that contain it.

Other questions

Do I need a vitamin C supplement?

Generally, it is better to get your nutrients from food rather than pills. That being said, taking a daily vitamin C supplement will not harm you in any way and can increase your daily intake if you fail.

If you think you are not getting enough vitamin C in your diet, do not hesitate to take supplements in the recommended doses. At the same time, increase your intake of the following foods rich in vitamin C:

  • Red bell pepper (raw): 95 milligrams per 1/2 cup serving
  • Orange juice : 90 milligrams per 3/4 cup serving
  • Orange : 70 milligrams per medium-size fruit.
  • Kiwi : 64 milligrams per medium-size fruit.
  • Green bell peppers (raw): 60 milligrams per 1/2 cup serving
  • Broccoli (cooked): 51 milligrams per 1/2 cup serving
  • Strawberries (chopped): 49 milligrams per 1/2 cup serving
  • Brussels sprouts (cooked): 48 milligrams per 1/2 cup serving
  • Tomato juice : 33 milligrams per 1/2 cup serving
  • Melon : 29 milligrams per 1/2 cup serving
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