Vitamin Information Center

Vitamin A
•Found in animal foods and converted from beta-carotene in plant foods.
•Required for vision, gene expression, reproduction, embryonic development, red
blood cell production, and immune function.
•Prescription vitamin A derivatives are used to treat skin conditions (acne) and reti-
nitis pigmentosa (genetic eye disease).
•Defi ciency is rare in Canada, but common in developing countries due to malnutri-
tion. It causes night blindness, dry eyes and skin, and impaired growth.
•Drugs that deplete vitamin A: cholestyramine, colestipol, mineral oil, and neomycin.
•Supplements should be avoided by those at risk of lung cancer (smokers) or liver
toxicity (alcoholics, liver disease).
•Doses greater than 10,000 IU daily should be avoided by pregnant women due to the
risk of birth defects. Most prenatal vitamins provide 5,000 IU.
•Doses greater than 5,000 IU may increase risk of osteoporosis.
•Supplements of vitamin A beyond what is provided in a multivitamin are not rec-
ommended due to risk of toxicity. To avoid this risk, choose a multivitamin that
contains beta-carotene, which is converted to vitamin A in the liver, but is not as-
sociated with health risks.

Researchers at Rutgers have unlocked some of the mysteries of how the developing embryo reacts to fluctuations in the amount of vitamin A present in the maternal blood stream. Their results are presented in the February 28 issue of the Journal of Biological Chemistry.

The researchers studied the role of LRAT, a protein that facilitates the formation of vitamin A stores in the body, during embryonic development. In particular, they showed how LRAT protects developing tissues from potentially toxic levels of vitamin A that have been ingested by the mother. Although this function of LRAT had previously been hypothesized in adults, this is the first time that its role has been demonstrated during embryonic development.

The developing mammalian embryo is entirely dependent on the maternal circulation for its supply of retinoids, the vitamin A metabolites produced in the body. These are essential nutrients and they control the formation of the embryo’s heart, central nervous system, eyes and other important organs and tissues. Malformations of the developing embryo can occur when too little, or too much, vitamin A is consumed by the mother.

“We were looking for the mechanisms that allow the fetus to maintain adequate amount of retinoids, whether the mother has over- or under-consumed vitamin A,” said Dr. Loredana Quadro, an assistant professor in the Department of Food Science and member of the Center for Lipid Research at the Rutgers School of Environmental and Biological Sciences. “We also looked at the effects of different levels of vitamin A being transferred from the mother to the fetus.”

When vitamin A is ingested, it is converted into retinyl ester (RE) in the intestine from where it is secreted in the bloodstream packaged with other dietary lipids into lipoprotein particles called chylomicrons. The majority of dietary RE reaches the liver, the main body storage site of vitamin A. Under insufficient dietary vitamin A intake, the liver transforms RE into retinol (ROH), which is then secreted into the bloodstream bound to retinol-binding protein (RBP), its sole specific serum carrier, to be delivered to the target tissues. Upon intake through a specific membrane receptor named Stra6, ROH is ultimately converted to retinoic acid (RA), which is the active form of vitamin A. If tissue RA is in excess, it is transformed into inactive forms, such as 4-hydroxy retinoic acid or 4-oxo retinoic acid (OXO-RA) by the action of a specific enzyme named Cyp26A1.

“When we think about vitamin A, we think about one compound,” said Quadro. “But in reality, the term vitamin A comprises a family of different compounds. Each one has a slightly different action, and plays a different role.”

The Rutgers researchers took a closer look at how ROH is metabolized into RE and RA to maintain an optimal balance of retinoids during the formation of the embryo. Mutant mice lacking both RBP and LRAT were generated to perform this study, so as to interfere with the two main pathways of maternal vitamin A delivery to the fetus (ROH-RBP from the liver stores and RE of dietary origin).

“We hypothesized that the lack of ROH-RBP and LRAT would make the embryo more vulnerable to changes in maternal dietary vitamin A intake,” said Quadro “and our data proved this to be correct. Indeed, a severe embryonic vitamin A deficiency is readily attainable when the mothers are deprived of dietary vitamin A during pregnancy. Therefore, this strain turned out to be a very good model to study how embryonic development is affected by fluctuations in the amount of retinoids present in the maternal diet and hence in the maternal circulation”.

The researchers identified LRAT, Cyp26A1 and Stra6 as the three key molecular players that act in coordination to protect the developing tissues from potentially detrimental levels of vitamin A ingested by the mother. “Understanding vitamin A metabolism in the developing fetus could have broad implications,” said Quadro. “Consumption of large doses of dietary supplements and vitamins, including vitamin A, has become a very common practice in recent years, generating the necessity to investigate the effects of high doses of vitamin A intake at different stages of the lifecycle, including pregnancy and development. These studies expand our knowledge of maternal-fetal nutrition and dietary contribution to embryonic development and may ultimately provide new insight into appropriate dietary practices during pregnancy.”

The paper was previously published on the Journal of Biological Chemistry’s web site on December 19, 2007.

Source: Rutgers University

A multivitamin is needed by most individuals to provide all of the needed vitamin and mineral missing in ones diet to support proper bodily functions on a daily basis. Here are some nutrients that it provides in sufficient levels, which include vitamin A, vitamin D, B vitamins, vitamin C, vitamin E, and Minerals.

Vitamin A, which is important for normal vision, integrity of the skin and those cells lining the inner surfaces of the body, gene expression, reproduction, embryonic development, growth, and immune function, is most commonly found as beta-carotene in a multivitamin. Unless the person supplementing is diabetic, the body can convert beta-carotene into vitamin A as it is needed. Therefore, the risk of vitamin A deficiency is nearly nonexistent, while the daily value for vitamin A is 5,000 IU, although supplementation of up to 25,000 IU of beta-carotene is safe and effective.

Vitamin D has recently become more and more recognized by the greater public. Its main role in human nutrition is the absorption of calcium and phosphorus from the intestinal tract, which therefore promotes the mineralization of the bones. Vitamin D can be made in our body by ultraviolet rays of the sun converting a cholesterol derivative in the skin. The daily value for vitamin D is 400 IU, while a range of 400 to 1,000 IU is a good daily dosage.

The B vitamins are involved directly or indirectly in energy metabolism. Some B vitamins facilitate the energy-releasing actions themselves while others help to build new cells to deliver the oxygen and nutrients which allow the energy pathways to run. The B vitamins are also involved in the function of the nervous system. The daily value of these vitamins differ according to the B vitamin, with the dosage ranging from 10 to 100 mg, and the dosage for folic acid ranging from 400 to 800 mcg/day.

Vitamin C promotes collagen synthesis in the body, offers antioxidant protection against free radicals, supports thyroxin synthesis and amino acid metabolism, strengthens resistance to infection, and helps in the absorption of iron. The daily value for vitamin C is a simple 60 mg, but studies have safely used 500 to 3000 mg/day.

Vitamin E is very valuable and worth taking as a separate supplement to get the best dosage. It helps the body by providing antioxidant protection against free radicals, stabilizing cell membranes, regulating oxidation reactions, and protecting both polyunsaturated fatty acids and vitamin A. It has also been proven in studies that a natural vitamin E is three times more active in the human body than synthetic vitamin E at similar doses.

Minerals have often been overshadowed in importance by vitamins, but the need for them is vital as they are recognized as essential to human nutrition. Important minerals include calcium, magnesium, iron, zinc, copper, iodine, potassium, manganese, selenium, and chromium.

Calcium is necessary for the formation of bones and teeth as well as blood clotting and normal muscle and nerve activity. Adequate calcium helps to maintain good bone health and may reduce the risk for osteoporosis later in life. The daily value for calcium is 1,000 mg but some research suggests that higher doses may be beneficial.

Magnesium is important for muscle and nervous tissue function and helps with the formation of bones and teeth. Supplementing with magnesium may help to reduce indications of bone loss. Research has shown that supplementing with 250 to 750 mg/d of magnesium can help stop bone loss and increase bone mass.

Another important mineral is iron, which transports oxygen in the body and is also makes oxygen available for muscle contractions. It is also necessary for the utilization of energy. The daily value for iron is 18 mg, but if a deficiency is diagnosed doctors may recommend up to 200 mg/day of iron.

Zinc is associated with the hormone insulin, zinc is involved in making genetic material and proteins, immune reactions, transport of vitamin A, taste perception, wound healing, the making of sperm, and normal development of the fetus. The daily value for zinc is 15 mg, but for specific purposes, levels up to 60 mg/day can be recommended for a short time. However, increased zinc levels can lower copper levels, which is responsible for the formation of red blood cells and nerve fibers. Therefore, copper should be added if zinc is being consumed at higher levels.

Other important minerals include iodine, which is essential in regulating metabolic rate; potassium, which helps to maintain normal osmotic pressure of body fluids and the acid-base balance of the body; manganese, which activates enzymes and is involved in fatty acid metabolism and protein synthesis; selenium, which detoxifies products of oxidized fats, and is found in red blood cells; and chromium, which is necessary for the formation of glucose tolerance factor, a complex that works with insulin.

Most generic multiple vitamins found at mass market stores only supply the RDA for vitamins and minerals. When looking for a good multiple vitamins you should buy only name brands and read the label to see that the above mentioned vitamins and minerals are supplied in the recommended doses. If the one you look at doesn’t have the above listed potency then move to another brand that does supply what is needed for optimal health.

A multivitamin is needed by most individuals to provide all of the needed vitamin and mineral missing in ones diet to support proper bodily functions on a daily basis. Here are some nutrients that it provides in sufficient levels, which include vitamin A, vitamin D, B vitamins, vitamin C, vitamin E, and Minerals. Continue Reading…