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Vitamin C 101: Understanding Testing, RDAs, and The Benefits of Supplementation

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Vitamin C 101: Understanding Testing, RDAs, and The Benefits of Supplementation

Over 70,000 research papers have been published on vitamin C since its discovery in 1913, and likely for a good reason; Vitamin C has a wide range of effects on the body. This article will discuss what vitamin C is, including its role in the body and deficiency causes and symptoms. Vitamin C testing and sources, including food and supplements, will also be discussed.


What is Vitamin C (Ascorbic Acid)?

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin found in the highest concentrations in the eyes, adrenal glands, leukocytes (a type of white blood cell), pituitary gland, and the brain. Most animals can innately produce vitamin C; however, humans cannot and thus must take in vitamin C. The amount of vitamin C in the body at any given time ranges from (at the very low end) 300 milligrams (mg) to two grams.

What is Vitamin C’s (Ascorbic Acid’s) Role in The Body

Vitamin C has various roles in the body, including biosynthetic roles, antioxidant functions, immune regulation, and iron absorption.

Biosynthetic Roles

Vitamin C is necessary for the creation of collagen, L-carnitine, and certain neurotransmitters. Collagen is a part of connective tissue and can affect the structure and strength of connective tissue, as well as increase the risk of injury and rate of healing in the previously mentioned tissues. Vitamin C is essential for the proper formation of collagen. L-carnitine is an essential nutrient required for converting fat into energy, and the creation of l-carnitine is dependent upon vitamin C status. Vitamin C is necessary for the creation of the neurotransmitters dopamine, epinephrine and norepinephrine and can also affect and enhance the response of those neurotransmitters in addition to GABA, glutamate, and acetylcholine through its neuromodulatory actions.

Antioxidant Functions

Vitamin C is known as a potent antioxidant that has a remarkable ability to neutralize free radicals and their products, reactive oxygen species (ROS). ROS can damage cellular parts as well as damaging DNA and seem to play a role in the pathogenesis of cardiovascular disease, chronic inflammatory disease, and cancer. High ratios of ROS to antioxidants have also been seen in neurodegenerative diseases, depression, and cognitive impairment and also seem to play a role in the aging process. ROS are a natural byproduct of specific biochemical pathways in the body but can also be created as a result of environmental exposures, including pollution, cigarette smoke, and ultraviolet (UV).

Immune Regulation

The immune system is made up of two distinct sectors: the innate immune response and the adaptive immune response. The innate immune response is the first line of defense, and its response is the same to all foreign invaders. The adaptive immune response kicks in later, and its response is specific to the foreign invader. Vitamin C is necessary for a proper response from both the innate and adaptive immune response in that it helps in barrier protection and certain cellular responses and actions.

Iron Absorption

Iron is present in two primary forms in foods: heme iron and non-heme iron. Heme iron, as found in animal foods, is readily absorbed and utilized in the body. Non-heme iron, as found in plant foods, requires more of a process in order for it to become bioavailable to the body. Vitamin C aids in the absorption process and specifically enhances non-heme iron absorption.

What Causes Vitamin C (Ascorbic Acid) Deficiency

Vitamin C deficiency is rare in developed countries. However, cases do occur and can be caused by diets with limited food variety (specifically, diets low in fruits and vegetables). People with malabsorptive diseases of the gastrointestinal tract (Crohn’s disease, celiac disease) and chronic diseases such as end-stage renal disease are also at risk for a vitamin C deficiency. Smoking depletes levels of vitamin C and thus puts those at risk for deficiency; even second-hand smokers, or people exposed to smoke, may be at risk for vitamin C deficiency. Lastly, infants given boiled or evaporated milk are at risk for vitamin C deficiency, as the heating process can reduce the already small amount of natural vitamin C found in cow's milk.  

Vitamin C (Ascorbic Acid) Deficiency Symptoms

Vitamin C deficiency is referred to as scurvy. Scurvy can begin to occur when vitamin C intake is below 10 milligrams per day for one month. Symptoms include:

  • Fatigue
  • Malaise (general feeling of discomfort)
  • Petechiae (round, red, pinpoint spots on skin measuring less than 4 millimeters [mm])
  • Purpura (larger version of petechia, ranging from 4-10mm)
  • Ecchymosis (largest version of petechiae, measuring 10 mm or larger )
  • Joint pain
  • Delayed wound healing
  • Hyperkeratosis (thickening of the outer layer of skin)
  • Corkscrew hairs
  • Depression
  • Swollen and bleeding gums
  • Loss of teeth
  • Iron deficiency anemia
  • Death (if untreated)

Children with scurvy can also develop bone disease.

How to Test Vitamin C (Ascorbic Acid) Levels

Vitamin C levels can be tested in the blood. Testing for vitamin C, such as with the Vitamin C test offered by Access Medical Laboratories, should result in a level between 0.6-2 milligrams per deciliter (mg/dL). Vitamin C can also be found on micronutrient tests such as the Vibrant America Micronutrient Panel.


How to Make Sure You Are Getting Enough Vitamin C (Ascorbic Acid) in Your Diet

The Institute of Medicine at the National Academies formed a Food and Nutrition Board (FNB) that created Dietary Reference Intakes (DRIs) for vitamins and minerals. A Recommended Daily Allowance (RDA) is one type of DRI defined as the average daily intake needed to meet nutritional adequacy in 97-98% of the healthy population. In the event that there is not enough evidence to form an RDA, an Adequate Intake (AI) level is created. AIs are defined as levels assumed to reach nutritional adequacy.

RDAs for Vitamin C (Ascorbic Acid)

It’s important to note that smokers have a recommendation of an additional 35 mg of vitamin C in addition to their respective RDA.

Pregnant and lactating women often have different RDAs as compared to their female counterparts of the same age. The RDA for pregnant women aged 14-18 years is 80 mg, and for those 19+ years is 85 mg. For lactating women, the RDA for those 14-18 years is 115 mg, and for those 19+ years is 120 mg.

AIs were developed for infants to 1 year old. The AI for males and females from birth to six months is 40 mg. For male and female infants six months to 1 year, the AI is 50 mg.

Vitamin C can be sourced from foods and supplements.

Food Sources of Vitamin C (Ascorbic Acid)

Food Sources of Vitamin C (Ascorbic Acid)

Supplements of Vitamin C (Ascorbic Acid)

Vitamin C can be found in multivitamins, combination products, and as a stand-alone supplement. Various forms of vitamin C can be found in supplements, including ascorbic acids and mineral ascorbates, such as calcium and sodium ascorbate. Additionally, ascorbic acid can be found in combination products such as EsterC, which contains many different forms of vitamin C. There is no definitive evidence to suggest one form is superior to others, and the low cost of producing ascorbic acid leads to that form being generally recommended.

Vitamin C levels in supplements often range from 250 mg - 1,000 mg. While vitamin C has low toxicity, high amounts can cause unpleasant side effects such as diarrhea, abdominal cramping, nausea, and other gastrointestinal complaints. This is due to the limited ability of our body’s to absorb excess vitamin C. It’s thought that doses over 1,000 mg result in only 50% absorption and that the adverse effects mentioned above can occur at doses larger than 3,000 mg per day. Additionally, high doses of vitamin C can contribute to kidney stones in people with a history of kidney stones or kidney disease and worsening of gout. Lastly, those with hemochromatosis, a condition of excess iron, are advised to avoid vitamin C due to the enhanced absorption effect of iron from vitamin C.

The FNB also created the DRI measurement Tolerable Upper Intake Levels (ULs). ULs are defined as the maximum amount of a vitamin or mineral that is unlikely to cause side effects.

Upper Intake Levels (ULs) for Vitamin C

Pregnant and lactating women have ULs that match their respective age groups. There are no ULs for infants under the age of one, as formula and foods should be the only sources of vitamin C for that age group.



Vitamin C is a vitamin of paramount importance due to its wide-reaching effects on the body. We must receive vitamin C in the form of food and or supplements due to our bodies' lack of ability to synthesize vitamin C. Vitamin C testing can be helpful to ensure levels are not deficient or approaching deficiency. Vitamin C supplementation can be appropriate for those who may have low intakes of fruits and vegetables. However, care should be taken to avoid excess vitamin C, as it can lead to unpleasant side effects, and its absorption rate makes overconsumption a financial waste.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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