VITAMINS
Vitamin C
The vitamin C deficiency disease, scurvy, was recognized at least 3000 years ago but it was not until the 16th century that people realized that certain fruits and vegetables could prevent or cure the disease. In the late 18th century, English sailors carried limes on long voyages to ward off scurvy, causing them to be nicknamed "limeys". In 1928 vitamin C was isolated and shown to be the substance necessary to prevent and cure scurvy. In its pure form, vitamin C, which is also known as ascorbic acid, is a water soluble white powder. Humans are among the few species that cannot manufacture vitamin C and must obtain it from food.
What it does in the body
Vitamin C is involved in hundreds of vital biological processes in the body.
Collagen and connective tissue
The main role of vitamin C is in the manufacture of collagen. This protein forms the basis of connective tissue, the most abundant tissue in the body, and acts as a cementing substance between cells. It helps support and protect blood vessels, bones, joints, organs and muscles, and forms a sizable proportion of skin, tendons, the cornea of the eye, ligaments, cartilage, teeth and bone. Collagen forms a protective barrier against infection and disease, and promotes healing of wounds, fractures and bruises.
Immune system
Vitamin C is critical to immune function as it is involved in antibody production and white blood cell function and activity. Other functions include the production of interferon, an antiviral and anticancer substance. Vitamin C requirements are raised when the immune system is under stress.
Antioxidant properties
Vitamin C is a powerful water soluble antioxidant and plays a vital role in protecting against oxidative damage. It neutralizes potentially harmful reactions in the watery parts of the body, such as the blood and the fluid inside and surrounding cells. It also helps protect LDL cholesterol against free radical damage. This antioxidant action helps to protect against cancer, the effects of aging, heart disease, and an array of other health problems (See page 417 for more information.)
Hormones
Vitamin C is important in the synthesis of adrenal hormones and is depleted from the adrenal glands in times of stress.
Nervous system
Vitamin C plays a role in the manufacture of neurotransmitters. It is necessary for the conversion of tryptophan to serotonin, and of tyrosine to dopamine and adrenaline.
Other functions
Vitamin C is involved in the manufacture of carnitine, a substance necessary for the production of energy from fatty acids in cells, especially cardiac and skeletal muscle cells. (See page 374 for more information.) Vitamin C is necessary for the activity of the enzyme system which metabolizes drugs in the body. It is also necessary for iron absorption and plays a role in the conversion of cholesterol to bile acids for excretion. Vitamin C may also affect prostaglandin metabolism.
Absorption and metabolism
Absorption of vitamin C occurs in the intestine. The amount absorbed depends on the dose as the absorption mechanism is saturable and any excess excreted in the urine in two to three hours. As vitamin C is water soluble, only a small amount (about 4 to 5 g) is stored in the body. Vitamin C levels in the body are regulated by absorption and kidney excretion mechanisms.
Deficiency
A lack of vitamin C leads eventually to scurvy. The symptoms are mainly due to poorly formed collagen and include the breaking open of small blood vessels, the reddening and bleeding of gums, loose teeth, joint pains, dry scaly skin and blood vessel damage. Other symptoms include general weakness, fluid retention, depression and anemia. Vitamin C deficiency can also cause slower wound-healing, increased susceptibility to infections, male infertility and increased genetic damage to sperm cells, which may lead to birth defects.
Scurvy and severe vitamin C deficiency are rare in developing countries but marginal deficiencies may be relatively common and may play a role in the development of diseases such as cancer and heart disease. The first National Health and Nutrition Examination Survey (NHANES I) looked at the vitamin C intake of over 11 000 people during a five-year period. Results showed that men whose intakes of vitamin C were greater than 50 mg daily had a 34 per cent lower chance of death from all causes than those whose intakes were lower than 50 mg daily.1
In a 1998 study, researchers at Arizona State University assessed the vitamin C status of nonsmoking college students during fall and winter. From one to two per cent of students were vitamin C-deficient and 12 per cent of those tested in the fall were marginally deficient while 16 per cent of those tested in winter were. If smokers had been included in the sample, it is likely that the number of students with deficiency would have been greater.2
Men, the elderly, smokers, diabetics, those with high blood pressure and perhaps oral estrogen-containing contraceptive users have lowered plasma vitamin C levels and are at greatest risk of deficiency-related diseases.
The vitamin C deficiency disease, scurvy, was recognized at least 3000 years ago but it was not until the 16th century that people realized that certain fruits and vegetables could prevent or cure the disease. In the late 18th century, English sailors carried limes on long voyages to ward off scurvy, causing them to be nicknamed "limeys". In 1928 vitamin C was isolated and shown to be the substance necessary to prevent and cure scurvy. In its pure form, vitamin C, which is also known as ascorbic acid, is a water soluble white powder. Humans are among the few species that cannot manufacture vitamin C and must obtain it from food.
What it does in the body
Vitamin C is involved in hundreds of vital biological processes in the body.
Collagen and connective tissue
The main role of vitamin C is in the manufacture of collagen. This protein forms the basis of connective tissue, the most abundant tissue in the body, and acts as a cementing substance between cells. It helps support and protect blood vessels, bones, joints, organs and muscles, and forms a sizable proportion of skin, tendons, the cornea of the eye, ligaments, cartilage, teeth and bone. Collagen forms a protective barrier against infection and disease, and promotes healing of wounds, fractures and bruises.
Immune system
Vitamin C is critical to immune function as it is involved in antibody production and white blood cell function and activity. Other functions include the production of interferon, an antiviral and anticancer substance. Vitamin C requirements are raised when the immune system is under stress.
Antioxidant properties
Vitamin C is a powerful water soluble antioxidant and plays a vital role in protecting against oxidative damage. It neutralizes potentially harmful reactions in the watery parts of the body, such as the blood and the fluid inside and surrounding cells. It also helps protect LDL cholesterol against free radical damage. This antioxidant action helps to protect against cancer, the effects of aging, heart disease, and an array of other health problems (See page 417 for more information.)
Hormones
Vitamin C is important in the synthesis of adrenal hormones and is depleted from the adrenal glands in times of stress.
Nervous system
Vitamin C plays a role in the manufacture of neurotransmitters. It is necessary for the conversion of tryptophan to serotonin, and of tyrosine to dopamine and adrenaline.
Other functions
Vitamin C is involved in the manufacture of carnitine, a substance necessary for the production of energy from fatty acids in cells, especially cardiac and skeletal muscle cells. (See page 374 for more information.) Vitamin C is necessary for the activity of the enzyme system which metabolizes drugs in the body. It is also necessary for iron absorption and plays a role in the conversion of cholesterol to bile acids for excretion. Vitamin C may also affect prostaglandin metabolism.
Absorption and metabolism
Absorption of vitamin C occurs in the intestine. The amount absorbed depends on the dose as the absorption mechanism is saturable and any excess excreted in the urine in two to three hours. As vitamin C is water soluble, only a small amount (about 4 to 5 g) is stored in the body. Vitamin C levels in the body are regulated by absorption and kidney excretion mechanisms.
Deficiency
A lack of vitamin C leads eventually to scurvy. The symptoms are mainly due to poorly formed collagen and include the breaking open of small blood vessels, the reddening and bleeding of gums, loose teeth, joint pains, dry scaly skin and blood vessel damage. Other symptoms include general weakness, fluid retention, depression and anemia. Vitamin C deficiency can also cause slower wound-healing, increased susceptibility to infections, male infertility and increased genetic damage to sperm cells, which may lead to birth defects.
Scurvy and severe vitamin C deficiency are rare in developing countries but marginal deficiencies may be relatively common and may play a role in the development of diseases such as cancer and heart disease. The first National Health and Nutrition Examination Survey (NHANES I) looked at the vitamin C intake of over 11 000 people during a five-year period. Results showed that men whose intakes of vitamin C were greater than 50 mg daily had a 34 per cent lower chance of death from all causes than those whose intakes were lower than 50 mg daily.1
In a 1998 study, researchers at Arizona State University assessed the vitamin C status of nonsmoking college students during fall and winter. From one to two per cent of students were vitamin C-deficient and 12 per cent of those tested in the fall were marginally deficient while 16 per cent of those tested in winter were. If smokers had been included in the sample, it is likely that the number of students with deficiency would have been greater.2
Men, the elderly, smokers, diabetics, those with high blood pressure and perhaps oral estrogen-containing contraceptive users have lowered plasma vitamin C levels and are at greatest risk of deficiency-related diseases.
