 | NUTRITIONAL
|  |
TABLE OF CONTENTS:
 INTRODUCTION / DEFINITION
| CONTAMINANTS IN FOODS
|
E-mail address gin@student.umass.edu
Last updated 5/22/97
| Toxicology is the science dealing with poisons or toxicants. Nutritional toxicology is the nutritional aspects of toxicology. It is not synonymous with food toxicology, although the two are related and overlap. Nutritional toxicology is concerned with toxicants in the diet and their interrelations with nutrition, whereas food toxicology deals with toxicants in foods. Nutritional toxicology is the branch of toxicology and nutrition concerned with the diet as a source of toxicants, the effects of toxicants on nutrients and nutritional metabolism on toxicants, and the scientific basis for regulatory decisions affecting toxicological safety of dietary components. Nutritional toxicology has many facets of extensive practical and theoretical importance. Nutrients |  |
| may act as toxicants when consumed in excess. Some of these toxicities, especially of Vitamins A and D, sometimes cause significant problems of human health. The diet may contain nonnutrients which are cause for toxilogical concern. Toxicants may alter nutrient intake, digestion, absorption, transport, activation, function, metabolism, or elimination. Conversely, food consumption, meal timing, nutrient intake, and nutritional status alter the actions, potencies, and detoxification of toxicants. Finally, nutritional toxicology is concerned with the scientific basis and consequences of regulatory decisions relating to control of toxicant residues in foods, e.g., setting legal tolerances or maximum permissible levels of natural toxicants such as aflatoxins. The responses of organisms to toxic substances vary widely depending on the organism and the identity of the substance, dose, route of administration, timing, synergists or antagonists, and numerous other factors. Depending on the substance and its specific effects, the response may be acute, subacute, or chronic. The toxic characteristics of a chemical may be descibed in terms of its qualitative type of toxicity, and in terms of its potency which is the quantitative ability of the substance to produce its effects. | |
Intakes of essential nutrients form a contiuum from lethally deficient to lethally excessive. Certainly for the usual range of nutrients to have any possibility of posing a toxic hazard, the nutrient must be extremely potent or capable of bioaccumulation. With naturally occurring concentrations of nutrients in foods, toxicity problems are primarily restricted to Vitamins A and D and, in some locations, to selenium or fluoride. Vitamins are essential to good health, yet the consumption of excessive amounts of some vitamins, particularly A and D, can lead to toxicity. With excessive nutrient supplementation, the list can be expanded to include niacin, ascorbic acid, sodium, and many other nutrients.
Naturally-occurring intoxications with vitamins are EXTREMELY RARE and result only from ingestion of 1) liver from animals that really pack away a lot of retinyl ester (Vitamin A) in their stellate cells (polar bear, shark, tuna, dogs, etc.) and 2) one of three or four plants containing vitamin D-like calcinogenic glycosides (1, 25 dihydroxycholcalciferol derivatives).
Vitamin Toxicity
 Vitamin A Toxicity
|  |
| |
Recommendations range from 2.5 micrograms (100IU) per day for adult Canadians to 10 micrograms per day for Canadian infants (400 IU). USRDA is 5 micrograms per day. 2000 IU daily poisons children, and especially sensitive kids have been intoxicated with less than half of that.
Active vitamin D increases gut absorption of calcium and phosphorus, resorption of calcium and phosphorus by the kidneys and increased bone turnover (needed for proper bone formation and mineralization, but also specifically promotes bone resorption).
The principal direct toxic effects of this fat soluble vitamin,vitamin D, are excessive absorption of calcium from the intestine and resorption of calcium from bone. This results in deposition of calcium and phosphorus in soft tissues all over the body, with particular damage to the heart, blood vessels and kidneys. This a fairly reliable method for inducing high blood pressure in model animals (such as dogs). This is presumably renal hypertension caused by calcification of the renal arteries. Extreme toxicities caused by the calcinogenic plants results in calcium deposition in and damage to lungs, tendons, ligaments with attendent lameness.
Nicotinic acid and nicotinamide are now known as the vitamin niacin, a water soluble vitamin.
All organisms need to absorb or make nicain, because it forms the active core of oxidation/reduction cofactors NAD and NADP. Without niacin, cells can not function and individual animals will die.
Toxic overdoses of niacin are not possible with natural foods, but are accomplished by ingestion of purified nicotinic acid or the even more potent nicotinamide supplements. "Megadoses" taken for reputed medical benefits have resulted in niacin toxicity and some less serious complications associated with vitamin C. When used at very high supermegadose levels of nicotinic acid (2000 to 4000 mg rather than the customary 5-20mg) as an adjunct to tryptophan treatment of depression or to lower blood cholesterol and raise HDL's, some patients report flushing (red skin), itching skin (urticaria), heartburn, nausea, etc
The important major minerals for healthy adults 19-50 yrs that cause side effects when taken in excess
| Phosphorous |  | The RDA for men and women is 1200 mg. Dietary sources of phosphorous are milk, cheese, yogurt, meat, poultry, grains, fish. Major function is bone and teeth formation and acid base balance. Excess intakes of this mineral can result in the depletion of body calcium and also erosion of the jaw. | ||
| Potassium |  | The RDA for men and women is 2000 mg. Dietary sources of potassium are leafy vegetables, lima beans, potatoes, bananas, milk, meats, coffee, and tea. Major function is fluid balance, nerve transmission, and acid base balance. Excessive intakes of this mineral can cause potassium build up and cardiac arrythmias if there is poor kidney function. | ||
| Sodium |  | The RDA is between 1100-3300 mg for men and women. Dietary sources are from common salt. It's major function is acid base balance, body water balance, and nerve function. Excessive amounts of this mineral will cause high blood pressure. | ||
| Chlorine |  | The RDA is 700 mg for mem and women. It is part of salt containing food, and also found in some fruits and vegetables. It is an important part of extracellular fluids. Along with excess intakes of sodium, it also contributes to high blood pressure. | ||
| Magnesium |  | The RDA is 350 mg for men and 280 mg for women. It is founn in whole grains, and green leafy vegetables. It's major function is activating enzymes, and involved in protein synthesis. Excess intakes of this mineral causes diarrhea. |
The important trace minerals for healthy adults 19-50 yrs that cause side effects when taken in excess
 Iron |  | The RDA for men is 10 mg and 15 mg for women. Dietary sources are from eggs, lean meats, legumes, whole grains, and green leafy vegetables. It is a constituent of hemoglobin and enzymes involved in energy metabolism. Excessive intakes of this mineral causes siderosis and cirrhosis of the liver. | ||
| Fluorine |  | The RDA for men and women is between 1.5-4.0 mg. Found in drinking water, tea, and seafood. It may be important in maintenance of bone structure. Excessive amounts of this mineral causes mottling of teeth, increased bone density, and neurologic disturbances. | ||
| Zinc |  | The RDA for men is 15 mg and 12 mg for women. It is widely distributed in foods. This mineral is a constituent of enzymes involved in digestion. Excessive amounts of this mineral causes fever, nausea, vomiting, diarrhea. | ||
| Copper |  | The RDA is 1.5-3.0 mg for men and women. Found in meats and drinking water. Constituents of enzymes associated with iron metabolism is it's major function. An excessive amount of this mineral causes a rare metabolic condition called Wilson's disease. | ||
| Selenium |  | The RDA is 0.070 mg for men and 0.055 mg for women. Found in seafood, meat, and grains. It functions in close association with vitamin E. Very high intakes of this mineral causes gastrointestinal disorders and lung irritation. | ||
| Iodine |  | The RDA is 150 mg for both men and women. Found in marine fish and shellfish, dairy products, vegetables, and iodized salt. It is a constituent of the thyroid hormone. Very high intakes of this mineral depresses thyroid activity. | ||
| Chromium |  | The RDA for males is between 0.075-0.25 mg for males and between 0.05-0.25 mg for females. Found in legumes, cereals, organ meats, fats, vegetableoils, meats, and whole grains. Constituent of some enzymes, and involved in glucose and energy metabolism. Excessive amounts of this mineral causes inhibition of enzymes. Also causes skin and kidney damage from occupational exposure. |
Natural toxicants in foods include inorganic elements, oxyanions, toxic proteins, peptides and amino acids, vaso and psychoactive substances, gitrogens and other sulfur containing compounds, mycotoxins and toxic stress metabolites, bacterial toxins, plant produced toxins of many types, and bioaccumulated substances. Some toxins affect very few people but occasionally do produce dramatic and sometimes lethal intoxications. Toxins may occur naturally in the plant or animal matter taken as food, or they may be produced by contaminating microorganisms.
Contaminants may enter the food chain at many different stages. Natural soil constituents, fertilizer ingredients and contaminants, irrigation water contaminants, and pesticides can enter through the roots of food crops. Contaminants in forages and other feeds can be transmitted to animal products. Veterinary pharmaceuticals and drugs given as growth stimulants can leave residues in animal products. Environmental chemicals such as lead and mercury from many sources have sometimes been significant food contaminants.
Lead is a naturally occurring element that has been used almost since the beginning of civilization. Because of the many industrial activities that have brought about its wide distribution, lead is ubiquitous in the environment today . All humans have lead in their bodies, primarily as a result of exposure to manmade sources. Lead enters the body primarily through ingestion and inhalation.
Today, the major environmental sources of metallic lead and its salts are paint, auto exhaust, food, and water. For children, the most important pathways are ingestion of chips from lead-painted surfaces, inhalation of lead from automobile emissions, food from lead-soldered cans, drinking water from lead- soldered plumbing, and medications in the form of folk remedies. The primary sources of environmental exposure to lead are leaded paint, auto emissions, and drinking water.
Food may contain lead from the environment or from containers. Agricultural vehicles are not required to use unleaded gasoline; consequently, lead can be deposited on and retained by crops, particularly leafy vegetables. Acidic foods have been found to leach lead from lead solder in cans and lead glazes used in making pottery and ceramicware. Water from leaded pipes, soldered plumbing, or water coolers is another potential source of lead exposure.
Once in the bloodstream, lead is primarily distributed among three compartments blood, soft tissue, and mineralizing tissue. The bones and teeth of adults contain more than 95% of total lead in the body. In times of stress, the body can mobilize lead stores, thereby increasing the level of lead in the blood.
For lead poisoning to develop, major acute exposures to lead need not occur. The body accumulates this metal over a lifetime and releases it slowly, so even small doses, over time, can cause lead poisoning. It is the total body burden of lead that is related to the risk of adverse effects. (fig. 4)
Fig. 4 Body burdens of lead in ancient people (left), typical american (middle), and clinical caseof lead-poisoning (right). Each dot represents 40ug of lead. (source)
| Frank wrist drop occurs only as a late sign of lead intoxication. (Fig. 2) | |
| Fig. 2 Chronic lead poisoning in an american house painter aged 60 years. 5 Years: Repeated attacks of lead colic. 18 Months: Bilateral Wrist-drop. 3 Weeks: Symmetrical Paralysis and waisting of Shoulder-girdle muscles. | ||
|  |
| |
 | Fig. 6 The Blue Line - a deposition of lead sulphide at the gingival margin associated with poor dental hygiene and lead poisoning. |
Whether lead enters the body through inhalation or ingestion, the biologic effects are the same; there is interference with normal cell function and with a number of physiologic processes. The lowest observable blood lead levels associated with specific health effects in chronically exposed children and adults are shown in Figure 5
The most sensitive target of lead poisoning is the nervous system. Lead affects primarily the peripheral and central nervous systems, the blood cells, and metabolism of vitamin D and calcium. Lead also causes reproductive toxicity. Neurologic deficits, as well as other effects caused by lead poisoning, may be irreversible.
Effects in children generally occur at lower blood lead levels than in adults. The developing nervous system in children can be affected adversely at blood lead levels of less than 10 ug/dL. Lead inhibits several enzymes that are critical to the synthesis of heme. Lead poisoning in children only rarely results in anemia. Lead-induced chronic renal insufficiency may result in gout. Lead interferes with a hormonal form of vitamin D, which affects multiple processes in the body, including cell maturation and skeletal growth. Maternal lead stores readily cross the placenta, placing the fetus at risk.
Effects of Toxicants on Nutrition
Toxicants can interfere with the intake, digestion, absorption, function, metabolism of nutrients. The effects include increased nutrient needs or decreased nutritional status.
A.) Modification of Nutrient Contents of Foods:
The earliest stage at which toxicants can affect nutrition is by alteration of the nutrien contents of foods.
Many toxicants can decrease food intake. Most toxic responses include growth depression, lethargy, metabolic inhibition, and loss of appetite. Decreased food intake may be a secondary effect of growth depression or inhibited cellular function, but with some toxicants loss of appetite is the primary effect which leads to other results.
Many toxicants inhibit digestion ,and assuming that digestion occurred or was not required for a particular nutrient, many toxicants have direct or indirect inhibitory effects on nutrien absorption.
Metabolism of nutrients includes modification, activation, and synthesis into the ultimately active forms of the nutrient, and metabolic processing and degradation into forms suitable for excretion. Toxicants, which prevent the anabolic reactions leading to execretory products, will have antinutritive effects. Some toxicants may inhibit both the synthesis of the ultimately active form of the nutrient and its function after synthesis. Nutrients involved in metabolic conjugation of toxicants are needed in increased amounts when the organism is exposed to those toxicants.
 | The National Center for Toxicological Research's mission is to conduct peer-viewed scientific research that supports and anticipates the FDA's current and future regulatory needs. This involves fundamental and applied research specifically designed to define biological mechanisms of action underlying the toxicity of products regulated by the FDA.This research is aimed at understanding critical biological events in the expression of toxicity and at developing methods to improve assessment of human exposure, susceptibility and risk. | |
| The National Toxicology Program (NTP) was established in 1978 by the Secretary of Health and Human Services to coordinate toxicology research and testing of potentially hazardous chemicals. The NTP is composed of sections of several Federal agencies that perform toxicology research. | |
| The EXTension TOXicology NETwork (EXTOXNET) is an effort of University of California, Davis, Oregon State University, Michigan State University, and Cornell University. Its purpose is to facilitate the exchange of toxicology-related information in electronic form, accessible to all with access to electronic mail (email) or the Internet. |
VITAMIN TOXICITY
