Health Benefits of Vitamin C

Can a daily supplement prevent colds and protect your eyes?

sources and supplements of vitamin c

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

Vitamin C has been used historically to prevent or treat scurvy and other illnesses associated with vitamin C deficiency. Today, it is widely touted as a natural defense against the common colds. Although vitamin C is considered to be an "immune booster," there is little evidence that taking it can actually prevent or treat an infection.

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

Health Benefits

The one condition vitamin C can most definitely treat is vitamin C deficiency. According to research from the Centers for Disease Control and Prevention (CDC), an estimated 7.1 percent of the U.S. population can be classified as being vitamin C deficient. Those will a severe dietary deficiency can develop scurvy, characterized by bruising, bleeding gums, weakness, fatigue, and rash.

Outside of a known deficiency, vitamin C is believed by some to aid in the treatment or prevention of numerous diseases, including colds, asthma, bronchitis, cancer, chronic pain, cataracts, gastritis, glaucoma, heart disease, high blood pressure, osteoarthritis, and Parkinson's disease.

Although the evidence supporting these claims is generally weak, there have some been several promising findings in recent years.

Common Cold

The benefits of vitamin C in fighting the common cold is more presumed than evidenced by research. According to a 2007 review of studies involving 13 clinical trials and 11,350 participants, vitamin C supplements did nothing to reduce the rate the colds compared to the general population.

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

A 2013 review from Finland similarly concluded that vitamin C cannot prevent colds but may shorten the course of the illness by up to 12 percent in adults and 21 percent in children with a daily 1,000- to 2,000-milligram dose.

Vision Loss

There is some evidence that vitamin C supplements may slow the progression of macular degeneration, an aging-related eye disorder characterized by vision loss.

A 2001 study in the Archives of Ophthalmology reported that people at high risk of the disease who took 500 milligrams of vitamin C per day, along with beta-carotene, vitamin E and zinc, slowed the progression of macular degeneration by 25 percent and the loss of visual acuity by 19 percent.

A 2014 review from Tufts University further concluded that taking 135 milligrams of vitamin C daily can prevent certain types of cataracts and that doses of over 300 milligrams could reduce the risk by no less than 57 percent.

High Blood Pressure

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

According to a 2012 study from Johns Hopkins University, high doses of vitamin C—around 500 milligrams daily—produced only small reductions in the systolic (upper) blood pressure but had little effect on the diastolic (lower) blood pressure.

While scientists have yet to establish why this is, it is thought that high doses of vitamin C have a mild diuretic effect that promotes the removal of excess fluid from the body. This may help lower the pressure within your blood vessels.

Heart Disease and Cancer

Vitamin C is often erroneously lauded for its ability to fight heart disease and cancer. Much of the misperception has been fueled by vitamin C's antioxidant properties.

While antioxidants can most definitely reduce the oxidative stress associated with these diseases, there is little to no evidence that vitamin C supplements can directly influence the risk.

Among some of the clinical findings:

  • An eight-year study involving 14,641 men over the age of 50 showed that a 400-IU dose of vitamin C did nothing to alter the rate of heart attacks or stroke compared to a placebo.
  • A nine-year study involving 8,171 older women demonstrated that 500 milligrams of vitamin C have no impact on the rate of cancer compared to the general population.
  • A 10-year study involving 77,721 older men and women also showed no association between vitamin C intake and the risk of lung cancer

Possible Side Effects

Although vitamin C is generally considered safe, high doses can cause adverse effects, including heartburn, nausea, headaches, stomach cramps, and diarrhea. Doses over 2,000 milligrams are considered extreme and may increase the risk of severe diarrhea and kidney stones.

While you can safely take vitamin C during pregnancy, excessive use may cause harm to the newborn. Generally speaking, between 85 and 120 milligrams per day is considered adequate.

Vitamin C can also raise your blood sugar and should be used with caution if you have diabetes. In older women with diabetes, vitamin C in amounts greater than 300 milligrams per day increases the risk of death from heart disease.

Drug Interactions

Vitamin C can slow the excretion of estrogen from the body. Taking vitamin C with estrogen or estrogen-based contraceptives may increase the risk of hormonal side effects.

The opposite may occur with the antipsychotic drug Prolixin (fluphenazine). When taken together, vitamin C can reduce the concentration of Prolixin in the bloodstream and reduce the drug's efficacy. Vitamin C supplements can also make certain chemotherapy drugs less effective.

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

Dosage and Preparation

When taken for general health, the recommended dietary allowance (RDA) of vitamin C is as follows:

  • Children 0 to 6 months: 40 milligrams per day
  • Children 7 to 12 months: 50 milligrams per day
  • Children 1 to 3 years: 15 milligrams per day
  • Children 4 and 8 years: 25 milligrams per day
  • Children 9 to 13 years: 45 milligrams per day
  • Females 14 to 18 years: 65 milligrams per day
  • Males 14 to 18 years: 75 milligrams per day
  • Females 19 and over: 75 milligrams per day
  • Males 19 and over: 90 milligrams per day
  • Pregnant females 14 to 18: 80 milligrams per day
  • Pregnant females 19 and over: 85 milligrams per day
  • Breastfeeding females 14 to 18: 115 milligrams per day
  • Breastfeeding females 19 and over: 120 milligrams per day

People who smoke should take an additional 35 milligram per day. Those with a diagnosed vitamin C deficiency should take between 100 to 200 milligrams per day until blood levels are normalized.

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

What to Look For

Not all vitamin C supplements are created equal. To better ensure quality and safety, choose supplements that have been tested and certified by an independent certifying body like the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International.

Also, be aware that there are different types of vitamin C, including L-ascorbic acid (typically derived from corn) and others that combine ascorbic acid with minerals (such as sodium or calcium), citrus bioflavonoids, or rose hips. None is considered better or more effective than the other.

If anything, you can save money by choosing a "plain" L-ascorbic acid supplements and avoiding all of the other non-essential add-ins.

Other Questions

Do I need a vitamin C supplement?

As a general rule, it is always best to get your nutrients from food rather than pills. With that being said, taking a daily vitamin C supplement won't cause you any harm and can bolster your RDA if you happen to fall short.

If you don't think you're getting enough vitamin C in your diet, don't hesitate to supplement at the recommended dosages. At the same time, increase your intake of the following foods rich in vitamin C:

  • Red pepper (raw): 95 milligrams per 1/2-cup serving
  • Orange juice: 90 milligrams per 3/4-cup serving
  • Orange: 70 milligrams per one medium fruit
  • Kiwi: 64 milligrams per one medium fruit
  • Green pepper (raw): 60 milligrams per 1/2-cup serving
  • Broccoli (cooked): 51 milligrams per 1/2-cup serving
  • Strawberries (sliced): 49 milligrams per 1/2-cup serving
  • Brussel sprouts (cooked): 48 milligrams per 1/2-cup serving
  • Tomato juice: 33 milligrams per 1/2-cup serving
  • Cantaloupe: 29 milligrams per 1/2-cup serving
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