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Issue # 65: A - Z of Nutrients Vitamin C
A to Z of Nutrients - Vitamin C
Vitamin C (ascorbic acid) is a ubiquitous compound, present in the physiologies of almost all plants and animals. Humans, other high primates, fruit bats and guinea pigs cannot produce their own bodily supply of vitamin C, and consequently require a regular dietary intake.
Vitamin C is an unstable water-soluble vitamin that is sensitive to heat, air, water (by leaching) and alkali (e.g. bicarbonate of soda). Certain metals, e.g. copper also speed the oxidative destruction of vitamin C.
What does it do?
Vitamin C has very many functions in the body - some still not completely understood. Below are listed some of the processes in which it is involved:
" Formation of collagen - the body's intracellular "cement" "
''Growth, tissue repair and wound healing''
" Formation of antibodies and stimulation of the white blood cells''
" Formation of corticosteroid hormones in the adrenal gland "
Absorption of iron and its necessary accumulation in the bone marrow, spleen and liver. " As an antioxidant nutrient, it protects water-soluble substances from oxidation by allowing itself to be oxidised. " As an anti-histamine, vitamin C reduces the effect of histamine produced by the immune system.
Histamine is responsible for many of the symptoms of allergies such as hay fever. " Carnitine formation in vegetarians, together with lysine.
What are the deficiency signs?
The classic vitamin C deficiency disease is scurvy, early symptoms of which are usually bleeding of the gums and loosening of the teeth, together with lassitude, weakness, irritability and muscle ache.
A prolonged marginal deficiency of vitamin C may not lead to clinical symptoms, but may predispose towards heart disease and lowered immunity.
Is it toxic?
Vitamin C is on the whole extremely safe, with no toxic effects even at dosages of grams per day. Transient diarrhoea is the usual side-effect that is noted when excess levels are taken.
The only other possibility of danger from high vitamin C intake occurs in people who have a family history of kidney stones, as oxalate can combine with calcium to form the stones. However, people who are not at high risk of kidney stones do not need to avoid vitamin C. Taking very high doses of vitamin C - 5000 mg a day and up - and then suddenly stopping the supplementation has been thought to possibly cause "rebound scurvy". However a recent review has shown there is no real basis for this belief. Nevertheless it is perhaps advisable to come off high level vitamin C slowly.
Who should supplement?
The daily requirement of vitamin C should be obtained through diet if current dietary guidelines are followed. However, those who are wishing to boost the immune system during the winter months may benefit from an extra vitamin C supplement. Intake levels: milligrams (mg) Upper safe level for daily supplementation = 2000mg Recommended Daily Allowance = 60mg (Smokers requirements are increased by 80mg)
Pepper, green 100
Brussels sprouts 90
Sweet Potato 25
Potatoes: new 16;
Oct-Dec 19; Jan-Feb 9; Mar-May 8
The main sources of vitamin C in the diet are potatoes, fruit juices, citrus fruit and green vegetables. The vitamin C content of foods varies very widely depending upon season, variety and freshness.
1.Vitamin and Mineral Safety, Council for Responsible Nutrition: 1997 2. Health Essentials, Vitamin Guide: 1994 3. Manual of Nutrition (MAFF): 1989
Vitamins are essential to maintain normal metabolic processes and balance within the body, and the role of vitamin C is probably the most varied of all vitamins making it the most versatile.
The amount of a specific vitamin required by an individual varies considerably and it is influenced by such factors as body size, growth rate, physical activity, and pregnancy. Most vitamins are stored minimally in human cells and vitamin C is no exception.
Vitamin C is a water-soluble vitamin, which means it is easily excreted by the body if it is not used quickly. It is for this reason that timed-release vitamins are useful for prolonging tissue saturation and preventing wastage of the water-soluble vitamins. However, the fat-soluble vitamins are stored in liver cells to a greater extent.
Vitamins A and D, for example, may be stored in sufficient amounts to maintain an individual without any intake for 5 to 10 months and 2 to 4 months, respectively. However, a deficiency of vitamin B compounds (except vitamin B12) may be noted within days, and the lack of vitamin C will manifest within weeks and may result in death in 5 to 6 months.
The current recommended dietary allowance (RDA) of vitamin C is 60 mg, which is based on the vitamin's role as an antioxidant as well as protection from deficiency. A severe deficiency of vitamin C will result in a state called scurvy, and it is thought that only 10mg of vitamin C is needed per day to prevent this.
Early symptoms of scurvy include excessive bleeding of the gums, and it is the ability of vitamin C to strengthen collagen fibres that causes this.
Collagen is one of the most abundant proteins in the human body and is incorporated into connective tissues, which include tendons, ligaments and blood vessels. All proteins are made up of amino acids and collagen is built using a repeating sequence of three amino acids called glycine, proline and hydroxyproline. Hydroxyproline is produced by the addition of oxygen to the proline amino acid once incorporated into the collagen structure, and this is achieved by vitamin C.
If vitamin C is absent, this conversion will not take place and the collagen fibre will break down causing weakened connective tissue and weakened arteries. This is primarily the reason why death can result if no vitamin C is consumed for 5-6 months. High intakes of the vitamin are generally well tolerated, and it is generally accepted that tolerance levels of vitamin C will vary among individuals.
Where some could easily consume 5g of vitamin C a day without experiencing any adverse effects, others may only be able to tolerate 500mg. Several populations warrant special attention with respect to vitamin C requirements. These include patients with periodontal disease, smokers, pregnant and lactating women, and the elderly.
Scientific studies have determined the effects of chronic vitamin C intake on the immune systems antioxidant defences during the immune response induced by intense exercise.
Blood samples were taken from 16 voluntary athletes in normal conditions, both immediately after and 1 h after a duathlon competition. Sportsmen's nutrient intakes were determined before the competition.
After determining the normal blood vitamin C levels, the results were analysed taking into account the vitamin C intake and their blood levels. Two groups were constituted; the vitamin C supplemented group and the control group, with the dietary vitamin C intake as the only statistical difference between groups. The intense exercise induced a significant increase in the production and distribution of white blood cells involved in the immune response, which was higher in the supplemented group.
The results showed that high vitamin C intake influenced the response of the immune systems antioxidant defences to oxidative stress induced by exercise. Therefore it can be concluded that high vitamin C intakes before intense exercise results in an increased immune response by white blood cells.
Free Radic Res. 2003 Sep;37(9):931-8
The antioxidant properties of vitamin C in the carotid body (tissue that monitors the levels of oxygen) make it a likely nutrient for detecting low blood oxygen levels. This study aimed to determine the effect of vitamin C on breathing rate in a population of elderly women, in whom blood oxygen and vitamin C levels may be deficient.
The study used 18 healthy females aged 60-80 years, and were given 1g of vitamin C twice daily. They found that vitamin C improved the detection of low blood oxygen levels by an average of 44%.
It was concluded that supplementation of vitamin C could improve the body's reaction to low blood oxygen levels.
J Int Med Res. 2003 Sep-Oct;31(5):448-57
Exposure to environmental tobacco smoke (ETS) has been linked to increased risk of lung cancer and heart diseases in non-smokers.
Current research suggests that some of these diseases are associated with increased damage to cells. A study investigated the effect of antioxidant (AO) intervention on damage in the blood of non-smokers exposed to ETS (passive smokers).
They measured cell damage in the blood of 67 passive smokers, at the beginning and after 2 months of daily intervention with AOs or placebo. The study subjects were randomised into one of three treatment groups: vitamin C, "mixture" (vitamin C, vitamin E, and a-lipoic-acid), and placebo.
Oxidative stress in subjects in the vitamin C and mixture groups decreased significantly when compared with the placebo group. Daily AO supplementation (especially with vitamin C) decreases damage to blood system cells in passive smokers. This finding might be of importance for the prevention of ETS-associated adverse health effects in non-smokers.
Nutr Cancer. 2003;45(2):176-84
Recent results indicate that cigarette smoke induces the damage of human blood proteins which is almost completely prevented by vitamin C.Cigarette smoke-induced damage of proteins and blood fats are accompanied by a decrease in the tissue vitamin C levels.
Also, the cigarette smoke-induced damage of proteins and lipid is reversed after discontinuation of cigarette smoke exposure accompanied by vitamin C therapy
The results indicate that comparatively large doses of vitamin C may protect the smokers from cigarette smoke-induced damage and associated degenediseases such as heart disease.
Free Radic Biol Med. 2000 Jul 15;29(2):115-24