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.

Take a minute to review and find your vitamin deficiencies – they may be a root cause of your symptoms, concerns, and health risks!

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.

Vitamin C status assessement

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.

Assessment of nutrient status brings cost-effective immediate answers when your client:

• Feels stressed, tired, depressed
• Takes prescription meds but cannot alleviate symptoms
• Wants to achieve optimal wellness, prevent chronic disease, and manage the aging process

Nutri-IQ™ is a unique tool that helps Wellness Professionals easily and conveniently identify clients’ nutritional gaps as possible causes for clients’ complaints.

Research has shown that the amount of vitamin C circulating in the blood can differ between individuals even when the same amount of vitamin C is consumed. This can be explained by individual genetic differences in a gene called glutathione S- transferase T1 (GSTT1), a member of a large family of detoxifying enzymes. GSTs work with vitamin C to reduce oxidative stress and they can spare each other from oxidation. One class of the GST enzyme family is the theta class, which consists of the GSTT1 enzyme.

There is a common “deletion” variant in the gene that codes for the GSTT1 enzyme. Those who have two copies of the “deletion” variant do not produce a functional GSTT1 enzyme. That means that an elevated risk genotype, and consuming adequate vitamin C consistently is necessary to reduce the risk of deficiency.

Vitamin C: Inadequacy & Risk

How to find out if someone is at risk? On the market, there is an enormous number of companies doing different types of genetic testing, and we had written about them in our article Genetic Testing for Nutritional Intervention. We however are recommending one only. Epigenetic tests from Canadian research company Nutrigenomix examine your genes to determine if they can trigger nutrient deficiencies, including vitamin C deficiency. These epigenetic tests are the BEST on the market!

• analysis of 77 genes and more than double polymorphisms (most companies do about 30 genes and about 100 polymorphisms)
• insights into nutrient metabolism, food intolerances and sensitivities
• confirmed 99% accuracy of the tests (most companies do not confirm accuracy)
• analyzed in Toronto lab using state-of-the-art genetic testing procedures

We will be glad to help you to get Nutrigenomix test done, explain findings, implement recommendations, and even assist with creating the daily menus.

Please note that these tests also only can be ordered through trained professionals.

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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.

Age	Male	Female	Pregnancy	Lactation
0–6 months	40 mg*	40 mg*
7–12 months	50 mg*	50 mg*
1–3 years	15 mg	15 mg
4–8 years	25 mg	25 mg
9–13 years	45 mg	45 mg
14–18 years	75 mg	65 mg	80 mg	115 mg
19+ years	90 mg	75 mg	85 mg	120 mg
Smokers	Individuals 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

Food	Milligrams (mg) per serving	Percent (%) DV*
Sweet red pepper, raw, ½ cup	95	106
Orange juice, ¾ cup	93	103
Orange, 1 medium	70	78
Grapefruit juice, ¾ cup	70	78
Kiwifruit, 1 medium	64	71
Sweet green pepper, raw, ½ cup	60	67
Broccoli, cooked, ½ cup	51	57
Strawberries, sliced, ½ cup	49	54
Cooked Brussels sprouts, ½ cup	48	53
Grapefruit, ½ medium	39	43
Broccoli, raw, ½ cup	39	43
Tomato juice, ¾ cup	33	37
Cantaloupe, ½ cup	29	32
Cabbage, cooked, ½ cup	28	31
Raw cauliflower, ½ cup	26	29
Baked potato, 1 medium	17	19
Raw tomato, 1 medium	17	19
Cooked spinach, ½ cup	9	10
Cooked green peas, ½ cup	8	9

• *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

• Elson Haas. “Staying Healthy with Nutrition”
• U.S. Department of Health & Human Services: https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/