Vitamin overdoses, toxicity

The water-soluble vitamins are the eight B vitamins and vitamin G. Because excesses are excreted rather than stored, it had previously been assumed that overdosing on water-soluble vitamins has no toxic effects. With the rise in popularity of megadoses of vitamins, some toxic reactions have been observed. It does, however, take much greater quantities of water-soluble vitamins to create harmful effects than for the fat-soluble vitamins. 

Proponents of this vitamin therapy often understand the risks of vitamin overdose. The scientific literature reports several well documented cases, sometimes with fatal consequences. Fat-soluble vitamins are of the Itighest concern in this respect, both acute (a single extremely large dose) or chrotuc (from continuous large doses) toxicity is known for them. It is not an accident that three of the four fat-soluble vitamins have widely accepted UL values, whereas water-soluble vitamins rarely have rehably known upper hmits. Studies of both hypo- and hyper-vitantin-osis contain enough scientific literature to fill libraries, and this short stoiy carmot even scratch the surface. Table 3.4 displays a few vitamins with reliable UL values and lists the symptoms of overdose. Care must be taken, as the toxic dose is usually lower for children than for adults, and the symptoms in kids may be more serious. 

Overdose Vitamin A toxicity in three children has been described [3 ]. 

Vitamin overdoses (hypervitaminoses)— The best known vitamin toxicities are those which result from vitamin A and vitamin D, because (1) these vitamins are fat soluble, (2) small amounts of them have strong effects, and (3) they tend to accumulate in the liver. Toxic effects do not occur so readily with vitamins E and K, which are also fat-soluble, unless high potency supplements are taken. 

Reported cases of vitamin toxicity owing to overdose are usually associated with increased over-the-counter availabiHty of supplemental vitamins and indiscriminate supplementation. The misconception that if a Httle is good a lot is better has compounded toxicological problems with the vitamins. Eat-soluble vitamins tend to accumulate in the body with relatively inactive mechanism for excretion and cause greater toxicological difficulties than do water-soluble vitamins. 

Since only a few vitamins can be stored (A, D, E, Bi2), a lack of vitamins quickly leads to deficiency diseases. These often affect the skin, blood cells, and nervous system. The causes of vitamin deficiencies can be treated by improving nutrition and by administering vitamins in tablet form. An overdose of vitamins only leads to hypervita mi noses, with toxic symptoms, in the case of vitamins A and D. Normally, excess vitamins are rapidly excreted with the urine. 

In foods vitamin B2 occurs free or combined both as FAD and FMN and complexed with proteins. Riboflavin is widely distributed in foodstnffs, but there are very few rich sources. Only yeast and liver contain more than 2mg/100g. Other good sources are milk, the white of eggs, fish roe, kidney, and leafy vegetables. Since riboflavin is continuously excreted in the urine, deficiency is qnite common when dietary intake is insufficient. The symptoms of deficiency are cracked and red lips, inflammation of the lining of the month and tongue, mouth ulcers, cracks at the comer of the mouth, and sore throat. Overdose of oral intake present low toxicity, probably explained by the limited capacity of the intestinal absorption mechanism [417]. 

The effects of most vitamin B overdoses have not been documented, although large dosages of pyridoxine have been reported to cause peripheral neuropathies. Ataxia and numbness of the hands and feet and impairment of the senses of pain, touch, and temperature may result. Excessive niacin intake may result in flushing, pruritus, and gastrointestinal disturbances. These symptoms are due to niacin s ability to cause the release of histamine. Large dosages of niacin can result in hepatic toxicity. 

Direct organ toxicity. Some substances may directly damage cells of a particular organ or system, either because they or their metabolites are specifically toxic to these cells, or because they are concentrated in one area, e.g. the renal fluoride ion toxicity of methoxyflurane, or the liver damage that occurs in paracetamol overdose because of a toxic intermediate product binding to hepatocytes. Secondary effects. Some effects are only indirectly related to the action of the drug, e.g. vitamin deficiency in patients whose gut flora have been modified by broad-spectrum antibiotics. 

Be cautious about overdosing on dietary supplements. Large doses of some nutrients act as drugs and prolonged heavy use can reach toxic levels. For example, too much Vitamin A can cause headaches, nausea, and diarrhea. High doses of Vitamin D can cause kidney damage. Too much iron can harm your liver. 

Chloramphenicol Palmitate Chloramphenicol has concentration-dependent incompatibility with many drugs. Chloramphenicol has severe toxic effects, and overdose may be treated by hemoperfusion of charcoal. It interacts with coumarin anticoagulants, some oral hypoglycemics, antiepileptic drugs, and nutrients such as iron and vitamin B12. 

It is now also recognized that overdoses of certain vitamins, especially some of the fat-soluble ones, may result in serious toxic effects. For this reason, the addition of vitamins to foods should be carefully controlled. 

A large single dose of vitamin D has biological effects for as long as 6 months (because of metabolism and storage). Thus the agent is cumulative and overdose by a mother anxious that her child shall have strong bones can cause serious toxicity. 

There is minimal tissue storage of water soluble vitamins in the body, therefore, water soluble vitamins are less likely to accumulate to toxic levels than are fat-soluble vitamins. In the case of an overdose of vitamins, fat-soluble vitamins are potentially more toxic than water-soluble vitamins. 

Hypervitaminosis K. Although it is possible to overdose with this vitamin, the fact that it is available only over the counter in small doses in multivitamin preparations has resulted in little knowledge of any toxicities. Toxicities do not appear in animals administered large doses. It is known that excess intake of the vitamin does not promote clot formation. There is no Tolerable Upper Intake Level. 

Reflect and Apply Give a reason for the toxicity that can be caused by overdoses of lipid-soluble vitamins. 

Micronutrients (vitamins and minerals) are also listed on food packaging. The vitamins we require are compounds that are necessary for metahohc processes either our bodies cannot synthesize them, or they cannot synthesize them in amounts sufficient for our needs. As a result, we must obtain vitamins from dietary sources. DVs are listed for the fat-soluble vitamins—vitamins A, D, and E (Section 8.7)—but care must be taken to avoid overdoses of these vitamins. Excesses can be toxic when lai e amounts of fat-soluble vitamins accumulate in adipose tissue. Excess vitamin A is especially toxic. With water-soluble vitamins, turnover is frequent enough that the danger of excess is not normally a problem. 

Lipid-soluble vitamins accumulate in fatty tissue, leading to toxic effects. Water-soluble vitamins are excreted, drastically reducing the chances of an overdose. 

Vitamin A is a lipid-soluble vitamin, which can accumulate in the body. Overdoses of this vitamin can be toxic. 

Because of their mechanism of action, bile acid sequestrants can potentially bind with and decrease the oral absorption of almost any other drug. Because these anion-exchange resins contain numerous positive charges, they are much more likely to bind to acidic compounds than to basic compounds or nonelectrolytes. This is not an absolute, however, because cholestyramine and colestipol have been reported to decrease the oral absorption of propranolol (a base) and the lipid-soluble vitamins. A, D, E, and K (nonelectrolytes). As a result, the current recommendation is that all other oral medication should be administered at least 1 hour before or 4 hours after cholestyramine and colestipol. Interestingly, this drug interaction has been used in a beneficial manner to treat digitalis overdose and toxicity. 

A. Acute overdose. Isoniazid produces acute toxic effects by reducing brain pyridoxal 5-phosphate, which is the active form of vitamin Bg and an essential cofactor for the enzyme glutamic acid decarboxylase. This results in lower CNS levels of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, which leads to uninhibited electrical activity manifested as seizures. INH may also Inhibit the hepatic conversion of lactate to pyruvate, exacerbating the lactic acidosis from seizures. 

Other symptoms of overdose of ginkgo seed may include abdominal pain, dyspnea, and other symptoms related to central nervous system disturbances (Bensky et al. 2004 Chen and Chen 2004). The compound 4 -0-methylpyridoxine, a neurotoxin that can cause vitamin B5 deficiency symptoms, is believed to be responsible for the toxic effects of ginkgo seed (Wada et al. 1985). Although... 

Some vitamins (A, D, E, and K) have very nonpolar molecular structures and therefore dissolve only in nonpolar solvents. In the body, the nonpolar solvents are the lipids we have classified as fats, so these vitamins are called fat-soluble. The fat-soluble vitamins have diverse functions in the body, and they act somewhat like hormones (Table 12.3). Care must be taken to avoid overdoses of the fat-soluble vitamins. Toxic effects are known to occur, especially with vitamin A, when excess amounts of these vitanfins accumulate in body tissue. Excesses of water-soluble vitamins are excreted readily through the kidneys and are not normally a problem. 

Vitamins are organic micronutrients that the body cannot produce in the amounts needed for good health. A number of vitamins have a high water solubility resulting from the highly polar nature of their molecules. All but one of the water-soluble vitamins are known to function as coenzymes in the body and are involved in many important metabolic processes. Fat-soluble vitamins have nonpolar molecular structures. As a result, they are insoluble in water but soluble in fat or other nonpolar solvents. Fat-soluble vitamins act somewhat like hormones in the body. Fat-soluble vitamins do not dissolve in water-based body fluids, so they are not excreted through the kidneys. Amounts in excess of bodily requirements are stored in body fat. Thus, it is much easier to produce toxic effects by overdosing with fat-soluble vitamins than with water-soluble vitamins. 

The risk of vitamin A overdose is exceptionally high as it has a relatively narrow safe range (the UL value is barely four times the RDA). Although adults are not expected to show symptoms of toxicity below one-time doses of about one hundred times the RDA, the regular consumption of 8000 pg/day already involves a significant risk of developing the symptoms of toxicity. Children are especially sensitive. Overdose in pregnant women may also lead to problems in the prenatal development of the fetus. 

Toxicity. Most cases of hypervitaminosis D found in the literature are the consequences of overdosing with either chole-calciferol or ergocalciferol. Toxic concentrations of vitamin D... 

Toxicity. Both of these members of the B complex vitamins are similar in their exceedingly low toxicity and adverse reactions. Biotin may have some influence on the inhibition of pentose phosphate pathway metabolism at extremely large overdoses (Marks, 1975). 

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