Vitamin C: Reference and Dietary Sources

Abstract

In this article, we describe:

  • the major purposes of this specific nutrient in the human body, 
  • its experimentally confirmed health uses, 
  • conventional ways to estimate nutrient status,
  • nutrient’s toxicities and deficiencies,
  • experimentally confirmed and approved levels of the nutrient intake for different demographics,
  • dietary sources of the nutrient.

Introduction

Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component.

Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters; and is also involved in protein metabolism. Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). Ongoing research is examining whether vitamin C, by limiting the damaging effects of free radicals through its antioxidant activity, might help prevent or delay the development of certain cancers, cardiovascular disease, and other diseases in which oxidative stress plays a causal role. In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function and improves the absorption of nonheme iron, the form of iron present in plant-based foods. Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility.

Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg/day. However, at doses above 1 g/day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine. Results from pharmacokinetic studies indicate that oral doses of 1.25 g/day ascorbic acid produce mean peak plasma vitamin C concentrations of 135 micromol/L, which are about two times higher than those produced by consuming 200–300 mg/day ascorbic acid from vitamin C-rich foods. Pharmacokinetic modeling predicts that even doses as high as 3 g ascorbic acid taken every 4 hours would produce peak plasma concentrations of only 220 micromol/L.

The total body content of vitamin C ranges from 300 mg (at near scurvy) to about 2 g. High levels of vitamin C (millimolar concentrations) are maintained in cells and tissues, and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and brain. Relatively low levels of vitamin C (micromolar concentrations) are found in extracellular fluids, such as plasma, red blood cells, and saliva.

Acute vitamin C deficiency leads to scurvy. The timeline for the development of scurvy varies, depending on vitamin C body stores, but signs can appear within 1 month of little or no vitamin C intake. Initial symptoms can include fatigue (probably the result of impaired carnitine biosynthesis), malaise, and inflammation of the gums. As vitamin C deficiency progresses, collagen synthesis becomes impaired and connective tissues become weakened, causing petechiae, ecchymoses, purpura, joint pain, poor wound healing, hyperkeratosis, and corkscrew hairs. Additional signs of scurvy include depression as well as swollen, bleeding gums and loosening or loss of teeth due to tissue and capillary fragility. Iron deficiency anemia can also occur due to increased bleeding and decreased nonheme iron absorption secondary to low vitamin C intake. In children, bone disease can be present. Left untreated, scurvy is fatal.

Today, vitamin C deficiency and scurvy are rare in developed countries. Overt deficiency symptoms occur only if vitamin C intake falls below approximately 10 mg/day for many weeks. Vitamin C deficiency is uncommon in developed countries but can still occur in people with limited food variety.

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Vitamin C inadequacy can occur with intakes that fall below the RDA but are above the amount required to prevent overt deficiency (approximately 10 mg/day). The following groups are more likely than others to be at risk of obtaining insufficient amounts of vitamin C: smokers and passive “smokers”; infants fed evaporated or boiled milk; individuals with limited food variety; people with malabsorption and certain chronic diseases (cachexia and some cancer patients).

Vitamin C has low toxicity and is not believed to cause serious adverse effects at high intakes. The most common complaints are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances due to the osmotic effect of unabsorbed vitamin C in the gastrointestinal tract.

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Recommended Dietary Allowances (RDAs) for Vitamin C

RDAs for vitamin C are based on its known physiological and antioxidant functions in white blood cells and are much higher than the amount required for protection from deficiency. For infants from birth to 12 months, the Adequate Intake of vitamin C is equivalent to the mean intake of vitamin C in healthy, breastfed infants.

AgeMaleFemalePregnancyLactation
0–6 months40 mg*40 mg*  
7–12 months50 mg*50 mg*  
1–3 years15 mg15 mg  
4–8 years25 mg25 mg  
9–13 years45 mg45 mg  
14–18 years75 mg65 mg80 mg115 mg
19+ years90 mg75 mg85 mg120 mg
SmokersIndividuals who smoke require 35 mg/day
more vitamin C than nonsmokers.

* Adequate Intake (AI)

Food Sources of Vitamin C

Fruits and vegetables are the best sources of vitamin C; examples include citrus fruits, tomatoes and tomato juice, red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, cantaloup, and potatoes are major contributors of vitamin C. Although vitamin C is not naturally present in grains, it is added to some fortified breakfast cereals. The vitamin C content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat. Steaming or microwaving may lessen cooking losses. Fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are usually consumed raw. Consuming five varied servings of fruits and vegetables a day can provide more than 200 mg of vitamin C.

Selected Food Sources of Vitamin C

FoodMilligrams (mg) per servingPercent (%) DV*
Sweet red pepper, raw, ½ cup95106
Orange juice, ¾ cup93103
Orange, 1 medium7078
Grapefruit juice, ¾ cup7078
Kiwifruit, 1 medium6471
Sweet green pepper, raw, ½ cup6067
Broccoli, cooked, ½ cup5157
Strawberries, sliced, ½ cup4954
Cooked Brussels sprouts, ½ cup4853
Grapefruit, ½ medium3943
Broccoli, raw, ½ cup3943
Tomato juice, ¾ cup3337
Cantaloupe, ½ cup2932
Cabbage, cooked, ½ cup2831
Raw cauliflower, ½ cup2629
Baked potato, 1 medium1719
Raw tomato, 1 medium1719
Cooked spinach, ½ cup910
Cooked green peas, ½ cup89
  • *DV = Daily Value.
  • The DV for vitamin C used for the values is 90 mg for adults and children age 4 years and older.  
  • Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

References

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