| | Vitamins are essential for the normal growth and development of a multicellular organism. Using the genetic blueprint inherited from its parents, a fetus begins to develop, at the moment of conception, from the nutrients it absorbs. The developing fetus requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other  things, skin, bone and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies have the potential to cause permanent damage.
For the most part, vitamins are obtained through food sources. However, a few vitamins are obtained by other means: for example, microorganisms in the intestine – commonly known as gut flora – produce vitamin K and biotin, and one form of vitamin D is synthesized in the skin with the help of natural ultraviolet in sunlight. Humans can produce some vitamins from precursors they consume: examples include vitamin A, which can be produced from beta carotene, and niacin, from the amino acid tryptophan.
Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues and organs that make up a multicellular organism. They also enable a multicellular life form (such as us) to efficiently use chemical energy provided by food eaten and to help process the proteins, carbohydrates and fats required for respiration. Vitamin deficiencies Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when you do not get enough of a vitamin in the food you eat. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, because of a “lifestyle factor,” such as smoking, excessive alcohol consumption or the use of medications that interfere with the absorption or the body's use of the vitamin. Individuals who eat a varied diet are unlikely to develop a severe primary vitamin deficiency. In contrast, restrictive diets have the potential to cause prolonged vitamin deficits, which may result in often painful and potentially deadly diseases.
Because humans do not store most vitamins in their bodies, we must consume them regularly to avoid deficiency. Human corporeal stores for different vitamins vary widely. Vitamins A, D and B12 are stored in significant amounts in the human body, mainly in the liver, and an adult human may be deficient in vitamin A and B12 for long periods of time before developing a deficiency condition. Vitamin B3 is not stored in the human body in significant amounts, so stores may only last a couple of weeks.
Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy) and vitamin D (rickets). In much of the developed world, such deficiencies are rare: this is due to 1) an adequate supply of food and 2) the addition of vitamins and minerals, often called fortification, to common foods. Vitamin side effects and overdose In large doses some vitamins have documented side effects. Vitamin side effects tend to increase in severity with increasing dosage. The likelihood of consuming too much of any vitamin from food is remote, but overdosing from vitamin supplementation does occur. At high enough dosages some vitamins cause side effects such as nausea, diarrhea and vomiting. Unlike some of the side effects caused by drugs, vitamin side effects rarely cause any permanent harm. When vitamin side effects emerge, recovery is often accomplished by reducing the dosage. Furthermore, the concentrations of vitamins an individual can tolerate vary widely and appear to be related to age and state of health. In the United States, overdose exposure to all formulations of vitamins was reported by 62,562 individuals in 2004 (nearly 80 percent of these exposures were in children under the age of 6), leading to 53 “major” life-threatening outcomes and 3 deaths – a small number in comparison to the 19,250 people who died of unintentional poisoning of all kinds in the U.S. in the same year (2004).
It is for these reasons that physicians and scientists carefully review the clinical data on supplement use in order to determine upper dosage thresholds for each vitamin that can be tolerated as a daily dose by the entire population without side effects. This dosage is known as the tolerable upper intake level (UL). Supplements Dietary supplements, often containing vitamins, are used to ensure that adequate amounts of nutrients are obtained on a daily basis, if optimal amounts of the nutrients cannot be obtained through a varied diet. Scientific evidence supporting the benefits of some dietary supplements is well established for certain health conditions, but others need further study.
Supplements are, as required by law, not intended to treat, diagnose, mitigate, prevent, or cure disease. In some cases, dietary supplements may have unwanted effects, especially if taken before surgery, with other dietary supplements or medicines, or if the person taking them has certain health conditions. Vitamin supplements may also contain levels of vitamins many times higher and in different forms than one may ingest through food. Before taking a supplement, it is important to check with a knowledgeable health care provider, especially when combining or substituting supplements with other foods or medicine. | |
Vitamin | Actions | Sources | Possible Effects of Taking Too Much | A (retinol, retinal, retinoic acid) | Needed for vision; maintains healthy skin and mucous membranes; key to immunity, tissue repair, bone growth and the development of embryos; acts as an antioxidant (protects the body from damaging substances called free radicals) | Liver, fish,dairy products, egg yolks, carrots, sweet potatoes, tomatoes, fortified breakfast cereals | Nausea; vomiting; headache; dizziness; blurred vision; clumsiness; birth defects; liver problems; possible risk of osteoporosis NOTE: You may be at greater risk of these effects if you drink high levels of alcohol, or you have liver problems, high cholesterol levels or don’t get enough protein. | B1 (thiamin) | Helps your body use carbohydrates for energy; good for your nervous system | Lean beef, pork, liver, legumes, nuts, enriched whole-grain products | None reported | B2 (riboflavin) | Helps your body process protein, carbohydrates and fats; helps maintain healthy skin | Lean beef, pork, liver, legumes, eggs, cheese, milk, nuts, enriched whole-grain products | None reported | B3 (niacin) | Helps your body process protein and fats; helps maintain a healthy nervous system, skin and digestion | Liver, turkey, tuna,
salmon, swordfish,
peanuts, beans,
yeast, enriched
whole-grain breads
and cereals | Flushing (redness) of the skin; upset stomach | B5 (pantothenic
acid) | Helps your body process nutrients; helps your body make red blood cells | Organ meats, beef, chicken, lobster, milk, eggs, peanuts, peas, beans, lentils, broccoli, yeast, cereals, whole grains | None reported | B6 (pyridoxine,
pyridoxal,
pyridoxamine) | Helps your body use protein and fats; supports your nervous and immune systems; helps your blood carry oxygen to your body’s tissues; helps break down copper and iron; prevents one type of anemia; helps maintain normal blood sugar levels | Organ meats, pork, beef, poultry, fish, eggs, peanuts,
bananas, carrots,
yeast, fortified cereals | Nerve damage to the arms and legs, which may cause numbness, trouble walking
and pain | B12
(cyanocobalamin) | Maintains healthy nerve cells and red blood cells; needed to make genetic material in cells; prevents one type of anemia | Liver, poultry, clams, sardines, flounder, herring, eggs, milk, blue cheese, fortified
cereals | None reported | C (ascorbic acid) | Helps form connective tissues, such as cartilage and tendons; acts as an antioxidant and protects your body’s cells from
damage from free radicals (by-products of metabolism); good for your immune system | Broccoli, green
peppers, spinach,
brussels sprouts, citrus fruits, tomatoes, potatoes, strawberries, cabbage | Upset stomach; kidney stones; increased iron
absorption | D (calciferol) | Helps your body absorb calcium and phosphorous; may help prevent fractures from osteoporosis; prevents rickets and osteomalacia (diseases that cause weak bones); helps immune system function | Saltwater fish, eggs from hens that have been fed vitamin D, fortified milk products and fortified cereals
NOTE: Vitamin D is
also made in your
body after you’ve
been in the sunlight.
| Nausea; vomiting; poor appetite; constipation;
weakness; weight loss; confusion; heart rhythm problems; deposits of calcium
and phosphate in soft tissues | E
(tocopherol) | Acts as an antioxidant; helps blood flow; helpsrepair body tissues | Fish, milk, egg yolks, vegetable oils, nuts, fruits, peas, beans,
broccoli, spinach,
fortified cereals | Risk is low
NOTE: If you take blood thinners, talk to your doctor before taking vitamin E pills.
| H (biotin) | Helps your body use nutrients; good for your nervous system; helps form red blood cells | Liver, kidney, egg yolks, peas, beans,
nuts, tomatoes, yeast | None reported | | K | Important for blood clotting and forming bones | Cheese, spinach,
broccoli, brussels
sprouts, kale,
cabbage, tomatoes,
plant oils, margarine | None reported
NOTE: If you take blood thinners, talk to your doctor before taking vitamin K pills.
| Folic Acid (folate) | Helps your body make and sustain new cells; prevents one type of anemia; prevents
neural tube birth defects | Dark leafy vegetables, dry
beans and peas,
oranges, fortified
cereals and grain
products | Risks are low
NOTE: High levels of folic acid may hide signs of B12
deficiency (a deficiency that
can cause nerve damage),
especially in older adults.
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