Vitamin C

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Vitamin C is a water-soluble vitamin that is used in many tissues throughout the body. The adrenal gland contains the highest concentration of vitamin C, and the vitamin plays a crucial role in both the adrenal cortex and adrenal medulla [1]. Humans are one of the few species that cannot manufacture the vitamin in the body and must depend on diet or nutritional supplementation as a source of vitamin C. The best sources of vitamin C are fresh fruit (especially in the citrus family, including oranges, lemons, limes and tangerines), strawberries, cantaloupe and currants. Green leafy vegetables, including Brussel sprouts, collard greens, lettuce, cabbage, peas and asparagus, are also good sources.

During the early days of sea exploration, European sailors were often afflicted with scurvy. Private firms would supply a ship’s crew with food for long voyages. These firms charged a flat rate, so the cheaper the food supplied, the more money a firm would make. Common sailors were given salt fish, salt beef and rye crackers, all of which lack vitamin C. The officers got a few extras including potatoes, which contain vitamin C and protected them against scurvy. Sailors from other parts of the world didn’t get scurvy because they ate foods containing vitamin C. The Vikings ate sauerkraut and the Chinese ate bean sprouts, both of which are high in vitamin C. The name chemical name for vitamin C, ascorbic acid, is derived from a-, meaning without, and scorbuticus, meaning scurvy.

Vitamin C possesses immunostimulatory, anti-inflammatory and anti-allergic properties to a variety of illnesses [2]. Many studies suggest that both the severity and duration of the common cold may be reduced with moderately high doses of vitamin C [3]. A study in 2002 showed that there were fewer colds and recovery was faster with individuals taking vitamin C [4]. These results were partially supported by a 5-year study published last year showing that vitamin C supplementation significantly reduced the frequency of the common cold; however, it had no apparent effect on duration or severity [5].

Vitamin C is required to form and maintain bones, skin and blood vessels. Collagen is the main ingredient in all fibrous tissue and is necessary for the health of skin, tendons, joints, bones, teeth and blood vessels. Collagen is also essential for the healing of wounds. Normal collagen synthesis depends upon the hydroxylation of the amino acids proline and lysine, forming hydroxyproline and hydroxylysine. The enzymes that catalyze this reaction require vitamin C as a cofactor (meaning a substance that is bound by an enzyme and is required for catalysis). In cases of chronic vitamin C deficiency, hydroxyproline and hydroxylysine are not formed in appreciable amounts and the resulting collagen fibrils are considerably weaker. This condition leads to weakened enamel of the teeth, gingivitis (inflammation of the gums) and bleeding gums, swollen and painful joints, rough dry scaly skin, easy bruising, dry and splitting hair and decreased wound-healing rate. A severe form of vitamin C deficiency is known as scurvy, which mainly affects older, malnourished adults.

As we age, there is a reduction in bone mineral density, or osteoporosis. It is important to slow this process and maintain strong, healthy bones to decrease the risk of bone fractures. An estimated 44 million Americans, 55% of the people 50 years of age and older, have osteoporosis. In the U.S., 10 million individuals are estimated to already have the disease and almost 34 million more are estimated to have low bone mass, placing them at increased risk for osteoporosis. Of the 10 million Americans estimated to have osteoporosis, eight million are women and two million are men [6]. Especially when used in conjunction with other therapies, many studies have demonstrated that vitamin C helps to support bone mineral density [7-9].

Vitamin C functions as an antioxidant, helping to limit damage to the body from free radicals. Additionally, vitamin C enhances the antioxidant activity of vitamin E. Studies suggest that vitamin C may reduce the risk of many kinds of cancer [10]. Chemotherapy leads to an increase in reactive oxygen species, which stresses the body’s antioxidant defense system. Low antioxidant vitamin intake, especially of vitamin C, have been associated with increased adverse effects of chemotherapy [11]. However, due to concerns regarding potential negative interactions with chemotherapy [12], antioxidant supplementation is not encouraged without advising a patient’s conventional health care provider. Increased intake of vitamin C may also reduce the chances of developing diabetes [13-14].

Vitamin C possesses antihistamine activity and may help reduce allergy symptoms [15]. Vitamin C deficiency has also been associated with an increased risk of developing asthma [16]. Indeed, in a recent study plasma ascorbic acid was found be lower in severe compared with mild-to-moderate asthmatics [17].

Vitamin C is required for synthesis of dopamine, noradrenaline and adrenaline (hormones that help the body respond to physical stress) in the nervous system or in the adrenal gland. Vitamin C is also necessary to synthesize carnitine, which is required for the oxidation of fatty acids. In a recent study, ascorbic acid was found to protect rats against the effects of high fat diets, reducing the increase in body weight, total body fat and enlargement of adipose deposits without affecting food intake [18]. Vitamin C may help decrease total and LDL cholesterol and triglycerides, as well as increase HDL levels [19-20]. However, antioxidants have been found to blunt the effects of niacin and simvastatin alone [21].

Because of its acid content, physicians recommend taking a buffered form of vitamin C if you are taking it in higher doses. Vitamin C in high doses (more than 2,000 mg daily) can cause diarrhea, gas, stomach cramps, nausea and may increase the risk of developing kidney stones. High doses of vitamin C can also deplete the body of copper, an essential nutrient. Vitamin C increases the absorption of iron and should be avoided by people with iron overload diseases. People who have kidney problems should check with a healthcare provider before taking vitamin C supplements. Infants born to mothers taking 6,000 mg or more of vitamin C may develop rebound scurvy due to the sudden drop in their daily intake.

References

1. Patak et al. Vitamin C is an important cofactor for both adrenal cortex and adrenal medulla. Endocr Res. 2004 Nov;30(4):871-5.
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2. Anderson R. The immunostimulatory, antiinflammatory and anti-allergic properties of ascorbate. Adv Nutr Res. 1984;6:19-45.
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3. Pauling L. How to Live Longer and Feel Better. New York: W.H. Freeman and Company; 1986:118-21.
4. Van Straten and Josling. Preventing the common cold with a vitamin C supplement: a double-blind, placebo-controlled survey. Adv Ther. 2002 May-Jun;19(3):151-9.
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5. Sasazuki et al. Effect of vitamin C on common cold: randomized controlled trial. Eur J Clin Nutr. 2006 Jan;60(1):9-17.
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6. National Osteoporosis Foundation
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8. Hall and Greendale. The relation of dietary vitamin C intake to bone mineral density: results from the PEPI study. Calcif Tissue Int. 1998 Sep;63(3):183-9.
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10. Byers and Guerrero. Epidemiologic evidence for vitamin C and vitamin E in cancer prevention. Am J Clin Nutr. 1995 Dec;62(6 Suppl):1385S-1392S.
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11. Kennedy et al. Low antioxidant vitamin intakes are associated with increases in adverse effects of chemotherapy in children with acute lymphoblastic leukemia. Am J Clin Nutr. 2004 Jun;79(6):1029-36.
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12. Labriola and Livingston. Possible interactions between dietary antioxidants and chemotherapy. Oncology (Williston Park). 1999 Jul;13(7):1003-8; discussion 1008, 1011-2.
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13. Zhang et al. Maternal plasma ascorbic Acid (vitamin C) and risk of gestational diabetes mellitus. Epidemiology. 2004 Sep;15(5):597-604.
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14. Bates et al. Nutrient intakes; biochemical and risk indices associated with Type 2 diabetes and glycosylated haemoglobin, in the British National Diet and Nutrition Survey of people aged 65 years and over. Diabet Med. 2004 Jul;21(7):677-84.
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15. Bielory and Gandhi. Asthma and vitamin C. Ann Allergy. 1994 Aug;73(2):89-96; quiz 96-100.
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16. Hatch GE. Asthma, inhaled oxidants, and dietary antioxidants. Am J Clin Nutr. 1995 Mar;61(3 Suppl):625S-630S.
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17. Misso et al. Plasma concentrations of dietary and nondietary antioxidants are low in severe asthma. Eur Respir J. 2005 Aug;26(2):257-64.
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18. Campion et al. Diferential gene expression and adiposity reduction induced by ascorbic acid supplementation in a cafeteria model of obesity. J Physiol Biochem. 2006 Jun;62(2):71-80.
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19. Jialal et al. Physiologic levels of ascorbate inhibit the oxidative modification of low density lipoprotein. Atherosclerosis. 1990 Jun;82(3):185-91.
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20. Rezaian et al. The salutary effects of antioxidant vitamins on the plasma lipids of healthy middle aged-to-elderly individuals: a randomized, double-blind, placebo-controlled study. J Med Liban. 2002 Jan-Apr;50(1-2):10-3.
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21. Cheung et al. Antioxidant supplements block the response of HDL to simvastatin-niacin therapy in patients with coronary artery disease and low HDL. Arterioscler Thromb Vasc Biol. 2001 Aug;21(8):1320-6.
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