Vitamin A

Vitamin A was isolated in 1930, the first fat-soluble vitamin to be discovered. The body acquires some of its vitamin A through animal fats, the rest it synthesizes in the intestines from the beta-carotene and other carotenoids abundant in many fruits and vegetables.

Vitamin A is stored in the liver. Small amounts are also found in most human tissues in chemical forms called retinoids, a name related to the vitamin's critical effect on vision (and particularly on the retina of the eye).

Vitamin A is a fat-soluble vitamin, which means that it requires fats as well as minerals to be properly absorbed by your digestive tract. It occurs in two forms: Preformed vitamin A, also called retinol, which is found in foods of animal origin. The other form is Provitamin A, also called carotene and is most commonly found in fruits and vegetables. Carotene is the primary pigment of deeply colored fruits & vegetables. In nature, there are over 500 carotenoids, but the body can only convert about 50 of them to Vitamin A.

Vitamin A is essential for numerous intrinsic processes. The most well-known and understood process is that of vision. The retinal form of vitamin A is essential for the neural transmission of light into vision. Epithelial cells are highly dependent on retinoic acid and are commonly used to treat a variety of skin diseases. A developing fetus is also highly dependent on retinoic acid, as it is essential to the growth of the eyes, lungs, ears and heart. The retinoids are not only the most active form of vitamin A, but also a current area of interest to many scientists.

The carotenoids (which are precursors to vitamin A) are a potent family of antioxidants that include alpha-carotene, beta-carotene, lycopene, lutein, and zeaxanthin. Carotenoids quench singlet oxygen, which is not, chemically speaking a free radical, but is nevertheless highly reactive and can damage other body molecules. Carotenoids also act as anticancer agents, decrease the risk of cataracts and age-related macular degeneration (progressive damage to the eye), and inhibit heart disease.

The body converts beta-carotene into vitamin A as needed. Any leftover beta-carotene then acts as an antioxidant, breaking free radical chain reactions and preventing the oxidation of cholesterol. It also reduces the oxidation of DNA.

Vitamin D

Vitamin D is called the sunlight vitamin because the body produces it when the sun's ultraviolet B (UVB) rays strike the skin. It is the only vitamin the body manufactures naturally and is technically considered a hormone. It is a fat-soluble vitamin that has properties of both a vitamin and a hormone. It is required for the absorption and utilization of calcium and phosphorous. It is needed for growth, and it is especially important for the normal growth and development of bones and teeth in children. It also protects against muscle weakness and is involved in regulating the heartbeat.

It is also important in the prevention and treatment of breast and colon cancer, osteoarthritis, osteoporosis, and hypocalcemia; it enhances immunity and is necessary for thyroid function and normal blood clotting.

The form of vitamin D that we get from food or supplements is not fully active, but requires conversion by the liver, and then by the kidneys, before it becomes fully active. This is why people with liver and kidney disorders are at a higher risk for osteoporosis.

When the skin is exposed to the sun’s ultraviolet lights, a cholesterol compound in the skin is transformed into a precursor of vitamin D. Exposing the face and arms to the sun for fifteen minutes three times a week is an effective way to ensure adequate amounts of vitamin D in the body. Unfortunately, the body's ability to manufacture vitamin D appears to decline with age, so older adults may need to get more vitamin D through diet (fortified milk and fatty fish have good amounts) or supplements, whether they're exposed to sunlight or not.

Fish liver oils, fatty saltwater fish, dairy products, and eggs all contain vitamin D. It is also found in vegetable oils. Vitamin D is also formed by the body in response to the action of sunlight on the skin. Herbs that contain vitamin D include alfalfa, horsetail, nettle, and parsley.

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Vitamin A

Although vitamin A is probably best known for promoting and maintaining healthy eyesight, it has other important functions as well. One of its major contributions is to improve the body's resistance to infection. It does this in part by maintaining the health of the skin, mucous membranes, and other surface linings (intestinal tract, urinary tract, respiratory tract) so that harmful bacteria and viruses can't get into your body.

Another way that vitamin A boosts immunity is by enhancing the infection-fighting actions of the white blood cells called lymphocytes. Vitamin A is also vital to the growth of bones, the division of cells in your body, and to human reproduction.

Specifically, vitamin A may help to:

  • Promote healthy vision—This nutrient is involved in the proper functioning of the retina of the eye and is essential for the integrity of the mucous membranes surrounding the eyes. It is invaluable in preventing night blindness, and assisting the eye in adapting from bright light to darkness. Vitamin A eye drops (available over-the-counter) are also effective in treating a disorder known as dry eye, caused by a failure of the tear glands to produce sufficient fluid.

  • Ward off infections such as colds, flu, and bronchitis—By supporting the healthy maintenance of mucous membranes, vitamin A may be useful for fighting colds and other common infections. In the case of chronic bronchitis, the nutrient encourages healing of damaged lung tissue and may even help to prevent recurrences. In a Brazilian study of men with chronic lung disease, it was found that participants who were given 5,000 IU of vitamin A daily for 30 days could breathe more easily than those who took a placebo.

  • Fight cancer—This immune-system booster may be of value in combating breast and lung cancers and in increasing the survival rate of leukemia patients. It may also protect against the development of a melanoma (a form of skin cancer that is often malignant). In addition, some research indicates that cancer patients with high vitamin A levels respond particularly well to chemotherapy treatment.

  • Treat skin disorders, such as acne, eczema, psoriasis, and rosacea—Research has shown that vitamin A is vital for healthy skin. In the l940s, high doses were prescribed for conditions such as psoriasis and acne. This practice ended abruptly with the realization that such high doses are toxic.

    • Today, doctors commonly prescribe safer medications made from derivatives of vitamin A, such as retinoic acid (Retin A, a popular prescription cream for acne and wrinkles) and isotretinoin (Accutane, an oral drug prescribed for severe acne). Short of prescription medications, however, careful use of moderate oral doses--see the Dosage Recommendations Chart--may be key to promoting skin health.

  • Control cold sores—Vitamin A has well-known antiviral properties, and it may be worth trying orally to boost immunity. Liquid forms can even be applied directly to cold sores, also known as fever blisters, which develop as a result of a herpes simplex viral infection.

  • Correct hair and scalp problems—One of the signs of a vitamin A deficiency (albeit a severe one) is flakiness of the scalp. Correcting the deficiency may eliminate this often itchy and embarrassing condition. But keep in mind that more isn't always better when it comes to vitamins: Too much vitamin A (more than 100,000 IU a day) taken over a long time can actually cause hair loss (among other problems).

  • Encourage healing of minor burns, cuts, and scrapes—When applied to the skin, vitamin A cream or ointment can accelerate the healing of minor cuts, burns, and scrapes.

  • Protect against certain gastrointestinal problems—Because it is helpful in protecting the lining of the digestive tract, vitamin A may ease symptoms of inflammatory bowel disease and ulcers. A large study of doctors ages 40 to 75 showed that those who were least likely to suffer from ulcers of the duodenum (a part of the small intestine) were the ones who had the highest intake of vitamin A, mainly from a combination of diet, multivitamins, and supplements.

Vitamin D

By promoting the absorption and balance of calcium and phosphorous in the body, vitamin D strengthens the bones and teeth and also fosters normal muscle contraction and nerve function. It is also useful for promoting immunity and blood cell formation. In addition, Vitamin D supplements may slow or even reverse some cancers.

Specifically, vitamin D may help to:

  • Prevent osteoporosis—The body cannot absorb calcium from food or supplements without an adequate intake of vitamin D. If calcium levels in the blood are too low, the body will steal the mineral from the bones and supply the muscles and nerves with the amount they need. Over time, the loss of calcium in the bones can lead to osteoporosis, a disease in which bones become porous and prone to fractures. After menopause, women are particularly at risk for developing this condition. Vitamin D taken along with calcium plays a critical role in maintaining bone density.

    • In a study of 176 men and 213 women over age 65 done at Tufts University, those who took 500 mg of calcium and 700 IU of vitamin D daily for three years experienced a decrease in bone density loss. Moreover, the incidence of fractures was cut in half. In another study, of 3,270 healthy elderly French women, a daily dietary supplement of 1,200 mg calcium plus 800 IU of vitamin D lowered the incidence of hip fractures by 43% in just two years.

  • Protect against certain types of cancer—Some studies indicate that vitamin D may be useful in preventing cancer of the breast, colon, and prostate. In a clinical trial of 438 men, researchers reported that participants with colon cancer had lower blood levels of vitamin D than those who did not have the disease. In addition, the men with the highest intake of vitamin D were the least likely to get colon cancer. More studies are needed to support this finding and to determine if it is applicable to women.

  • Slow joint damage due to arthritis—One recent study showed that taking 400 IU or more of vitamin D daily was effective in delaying or stopping the progression of osteoarthritis of the knees. It did not, however, prevent the disease from developing.

  • Ease back pain—Individuals who are prone to back problems may benefit from taking vitamin D because of its ability to promote strong bones and cartilage.

  • Protect against multiple sclerosis—Preliminary animal research suggests a possible connection between high vitamin D levels and immunity to this disabling nerve disorder. This hypothesis may explain why both in the tropics (where there is ample sun to boost vitamin D levels) and in coastal Norway (where sun is scarce, but fatty fish rich in this nutrient abound and are eaten by the local population), cases of MS are rare. More studies in humans are needed, however.

  • Relieve the symptoms of psoriasis—Because it plays a role in skin cell metabolism and growth, vitamin D may be helpful in treating the itching and flaking associated with this skin ailment. A few studies show that individuals with psoriasis have low levels of this vitamin. Don't bother with over-the-counter vitamin D creams and supplements, however; they have little effect on psoriasis. Studies do show that a vitamin D3 derivative (1,25 dihydroxycholecalciferol), or activated vitamin D, which is available only by prescription in cream and supplement form, may be useful for psoriasis. It is thought to work by helping skin cells to replicate normally.

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