Vitamin C: food sources, functions, side effects and daily dosing

Vitamin C: food sources, functions, side effects and daily dosing
March 15, 2014 5:54 AM

Vitamins are organic molecules that are necessary for proper growth and functioning of human body. Vitamins actually act as “catalyst”. This means they speed up various chemical reactions taking place inside human body. Although vitamins are required by body only in small amount, yet their deficiency can result in impaired growth and a number of medical complications.

Vitamin C is one of the most important vitamins. Other name for vitamin C is “ascorbic acid”. Vitamin C is absorbed through small intestine and is distributed widely throughout the whole body. Since it is a water soluble vitamin, it is excreted through urine which means we need to consume this vitamin on daily basis to maintain an optimum level of this vitamin. Some animals and lower mammals have the ability to synthesize vitamin C in their body but humans lack such ability. Hence humans are totally dependent on dietary sources for fulfilling their requirement for vitamin C.

Food sources of vitamin C

It is a misconception that only citrus fruits contain vitamin C. No doubt these fruits are the richest natural sources of vitamin C but there are many other fruits and vegetables that contain vitamin C in high quantity. Some plentiful sources of vitamin C are given below.

Vitamin C containing fruits are:

  • Citrus fruits like lemon, oranges and grape fruits
  • Cantaloupe
  • Kiwi
  • Apricots
  • Mangoes
  • Papaya
  • Pineapple
  • Strawberries
  • Raspberries
  • Blueberries
  • Watermelon
  • Avocado
  • Guavas
  • Cherries
  • Peaches
  • Pears
  • Bananas
  • Plum

Vitamin C containing vegetables are:

  • Leafy vegetables
  • Cauliflower
  • Cabbage
  • Green peas
  • Tomatoes
  • Beans
  • Potatoes
  • Broccoli
  • Brussels sprouts
  • Turnip
  • Chili peppers
  • Spinach
  • Onion
  • Bell pepper
  • Green bell pepper
  • Squash
  • Asparagus
  • Artichoke
  • Cucumber

Kale Animal food sources of vitamin C are:

  • Calf liver
  • Beef liver
  • Lamb liver
  • Lamb heart
  • Calf adrenals

Functions of vitamin C

When it comes to beautiful and glowing skin, the first thing that comes to mind is vitamin C. Vitamin C is considered as a key to flawless and fresh looking skin. That is why vitamin C rich citrus fruits like lemons are used in various natural remedies for skin problem. But apart from this, vitamin C plays many important roles in human body.

Let’s discuss the functions of vitamin C one by one in detail:

Collagen synthesis

The main function of vitamin C is to assist the body in the synthesis of collagen. Collagen is an elastic, structural protein that is the chief component of connective tissues, cartilages, bones, blood vessels, skin, tendons, ligaments and teeth. Collagen molecules consist of 3 chains of amino acids twisted around each other in the form of triple helix.

Collagen molecule remains structurally functional as long as its helical configuration is preserved. These collagen molecules contain two amino acids named as proline and lysine that need to be hydroxylated to maintain the helical structure of collagen chains. The enzyme responsible for this hydroxylation is known as hydroxylase. Like any other enzyme, this hydroxylase enzyme needs a co-factor for its functioning. Now here comes the role of vitamin C.

Vitamin C acts as co-factor of hydroxylase enzymes. Vitamin C accelerates the hydroxylation of proline and lysine by assisting the hydroxylase enzyme. Thus by speeding up the hydroxylation step of amino acids, vitamin C helps in maintaining the structural stability of collagen.

Since collagen is responsible for maintaining the structural integrity of many important structures in the body, its deficiency would lead to several medical condition. This happens in case of vitamin C deficiency. Severe deficiency of vitamin C results in a disease called “scurvy” in which there is defective synthesis of collagen molecules. Deficiency of vitamin C stops the hydroxylation of amino acid, ultimately resulting in the accumulation of faulty collagen chains. Vitamin C deficiency or scurvy results in swollen bleeding gums, fractures of bones, internal bleeding and poor wound healing.

Wound healing

Wounds are healed when connective tissue is deposited to bridge the gaps. Vitamin C helps in the accumulation of connective tissues in wounds by stimulating the synthesis of collagen fibers. Thus, vitamin C is essential for proper wound healing and for maintaining the tensile strength of scar tissue. Deficiency of vitamin C results in poor wound healing and bleeding.

Bone deposition

The bones contain certain bone forming cells called “osteoblasts”. The function of these cells is to deposit connective tissue that maintains the strength of bones. Vitamin C stimulates these osteoblasts to deposit more and more connective tissue. Vitamin C deficiency may results in skeletal problems like weak bones and fractures.

Healthy skin

Collagen or connective tissue is an important component of skin tissues. Vitamin C keeps the skin firm, taut, healthy and wrinkle free by increasing the collagen production in skin layers.

Vitamin C as an antioxidant

Vitamin C is an important antioxidant. It scavenges the harmful “free radicals” produced in body. Free radicals are reactive oxygen molecules that contain unpaired electrons. These reactive free radicals are very harmful for body tissues and cells because they cause the oxidation of cellular membranes, proteins and DNA, resulting in cell damage. But vitamin C has the ability to fight against these injurious free radicals. Ascorbic acid tends to stabilize these free radicals by donating them electrons.

Some antioxidants roles of vitamin C are as follows:

  • In heart diseases: Vitamin C is helpful in reducing the risks of heart diseases and strokes. Free radicals in body cause oxidation of LDL molecules (low density lipoproteins) or bad cholesterol. These cholesterols molecules are then deposited into arterial walls, resulting in the formation of atherosclerotic plaques. Vitamin C prevents the formation of theses plaques through its antioxidant role.
  • In cancer: Cancer arises when the cell DNA is mutated. Free radicals have the tendency to cause mutations in DNA. Studies show that vitamin C reduces the risks of cancer by suppressing the oxidation of DNA molecules.

Immunity booster

Vitamin C is commonly used as a natural remedy for common cold and sore throat. It helps in boosting the immunity by increasing the life span of immunity producing white blood cells. Vitamin C also helps in limiting the infection and inflammation by neutralizing the toxic compounds produced as the result of inflammatory response to infection.

Synthesis of neurotransmitters

Vitamin C helps in the synthesis of neurotransmitters like catecholamine. It acts as co-factor for enzyme dopamine hydroxylase, which converts dopamine to norepinephrine or catecholamine.

Energy production

Vitamin C enhances the synthesis of carnitine, a protein that helps to pump the fatty acids into the mitochondria for the production of ATP or energy.

Side effects of vitamin C

The side effects of vitamin C are very rare but their possibility cannot be ruled out. The upper limit of vitamin C which can be tolerated by an individual is 2000mg or 2g per 100g. Some possible side effects of vitamin C are:

Gastrointestinal disturbance

Consuming vitamin C more than the recommended dosage can cause gastrointestinal troubles like nausea, vomiting and indigestion problems. Taking too much vitamin C may cause diarrhea. Prolonged diarrhea and vomiting may lead to dehydration, mineral depletion and increased thirst.

Neurological problems

Consuming high doses of vitamin C over a prolonged period of time may cause migraine, headache, dizziness and faintness. But these side effects occur very rarely.

Hematochromatosis

Hematochromatosis is a hereditary condition in which excess iron is absorbed and stored in body, resulting in iron overload. Vitamin C promotes the absorption of iron in the body. So, toxicity of vitamin C will exacerbate Hematochromatosis by increasing the iron absorption by many folds. However, vitamin C toxicity itself cannot lead to Hematochromatosis. It can only worsen the symptoms of disease in patients suffering from it.

Insomnia

Too much consumption of vitamin C keeps the level of catechlomines always high in the body. These neurotransmitters produce a sense of alertness, making it difficult for a person to sleep well.

Kidney stones

The breakdown products of vitamin C are oxalates that are excreted through urine. Those people who take vitamin C supplements have high urinary oxalate output. These oxalate crystals have the tendency to precipitate and form stones in the kidneys. Therefore, consuming too much vitamin C daily might increases the risks of kidney stones formation.

Recommendations of vitamin C

The safe limit of each vitamin depends upon its RDA value. RDA stands for recommended dietary allowance, which means the amount of vitamin a person should consume every day.

The RDA value of vitamin C varies with different age groups:

  • For infants: 0-6 months: 40mg/day 7-12 months: 50mg/day
  • For children: 1-3 years: 15mg/day 4-8 years: 25mg/day
  • Women: Age 9-13 years: 45mg/day Age 14-18 years: 65mg/day Age 19 years and older: 75mg/day Pregnant females (14-18 years): 80mg/day Pregnant females (19 years and older): 85mg/day Lactating females (14-18 years): 115mg/day Lactating females (19+ years): 120mg/day
  • Men: Age 9-13 years: 45mg/day Age 14-18 years: 75mg/day Age 19 years and older: 90mg/day
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Written by: Michal Vilímovský (EN)
Education: Medical student, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic
Published: March 15, 2014 5:54 AM
Next scheduled update: March 15, 2016 5:54 AM
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