1、ALUMINUM AND HEALTH A REVIEW OF THE ISSUES, THE EFFORTS AND THE KNOWLEDGE SEYMOUR G. EPSTEIN TECHMCAL CONSULTANT THE ALUMINUM ASSOCIATION, INC. FOREWORD When this paper was first published in 1984 we indicated then our intention to update it to incorporate new findings and revised theories as they a
2、re developed. We continue to fund research and to follow closely the literature on aluminum and health. In that way we hope to have the latest information that accurately represents the state of our knowledge of aluminum and health at the time of publication. In recent years, oversight of the Alumin
3、um Industrys Health Research Program has been delegated to a Global Health Research Working Committee comprised of representatives of major aluminum companies, The Aluminum Association, national aluminum associations of Brazil, Canada, France, and Japan, the European Aluminium Association and the In
4、ternational Aluminium Institute. The Task Force meets regularly, obtains funding for needed research on all aspects of aluminum and health, and monitors the projects to completion. I am happy to report that The Aluminum Association continues to play a key role in this activity. J. Stephen Larkin * P
5、resident The Aluminum Association September 2003 INTRODUCTION In 1886, the first practical and economic process for producing aluminum metal was discovered. Cookware was the first commercial application for the new metal. It was not long after that salesman of competing cookware alleged various adve
6、rse health effects from exposure to aluminum. The first comprehensive treatise on aluminum compounds in food was published in 1927l. The author, Dr. E.E. Smith, then a fellow and former president of the New York Academy of Sciences, presented considerable evidence that aluminum is not injurious to h
7、ealth. He added, “Unfortunately, this question has become controversial by reason of conflicting commercial interests.“ These claims have persisted despite the fact that the vast majority of the scientific and medical communities neither originate nor support them. To the contrary, the U.S. Food and
8、 Drug Administration considers metallic aluminum and a number of aluminum compounds as “GRAS“: Generallv Recognized As Safe. The Aluminum Associationt in 1955 asked scientists at the Kettering Laboratory of the University of Cincinnati to search out and review the worlds literature on aluminum and h
9、ealth. The investigators reviewed more than 800 books and technical articles, and published their findings in 1957 in the American Medical Associations Archives of Industrial Health.2 They concluded that there is no need for concern among the public regarding hazards to human health from exposure to
10、 aluminum products. The review was updated in 1974 by Kettering researchers to include an additional 700 publications, and the results were published in Environmental Health perspective, a publication of the National Institute of Environmental Health Sciences. The basic conclusions were reaffirmed.
11、Allegations concerning neurological effects of aluminum began appearing in the media in the mid- 1970s. Aluminum, it was claimed, caused * References are found at the end of the paper. The Aluminum Association is a non-profit organization that represents aluminum companies in the United States and a
12、broad. Its member companies produce primary and secondary aluminum metal and semi-fabricated mill products. senility and was deemed a factor in Alzheimers disease (AD), then known as “presenile dementia.“ Recommendations were made to avoid aluminum in the diet and to avoid aluminum products for cook
13、ing or storing foods. These claims and “medical recommendations“ did not come from the scientific or medical communities but were loosely based on results of a few scientific studies then in progress. A task force of the Aluminum Associations Health Committee visited several leading investigators fo
14、r first-hand discussions of these studies. We learned that aluminum was also being linked with two conditions occurring in some patients with kidney failure: “dialysis dementia,“ a fatal neurological disorder, and “osteomalacia,“ a bone disease. In 1979, the Association again turned to the Kettering
15、 Laboratory staff for an in-depth reGiew of the neurological implications of aluminum. The Kettering team published its report in 1981, entitled “Neurotoxicity of Aluminum.“4 Based on a critical review of about 90 articles, the report concluded that “there is at present no direct clinical or experim
16、ental evidence that aluminum is neurotoxic to humans or animals under ordinary conditions of environmental exposure.“ It was, however, felt that gaps exist in the knowledge of the significance of aluminum in the human body. This is principally because aluminum was not generally regarded as posing a
17、health problem in the past and, hence, drew little scientific interest or study. Between 1980 and 1988, a research team at the University of Cincinnati continuously monitored and reviewed the literature on all aspects of aluminum and health.56 Since 1988, the search and review of the literature has
18、been conducted for the Association at the New York State Institute for Basic Research in Developmental Disabilities (IBR). The need was recognized for basic information on the way aluminum gets into the body, how much typically is absorbed, where it goes, and what happens once it gets there. To obta
19、in this information, the Association set into place a long-range research program, including: o The establishment of a Center for Trace Element Studies at IBR to provide basic research into effects of aluminum in the brain and continuing review of the worlds literature on aluminum and health; 1 Fund
20、amental studies of Alzheimers disease at laboratories of the National Institute on Aging (NIA); Studies of absorption of aluminum in the human body at the Harwell Laboratories of AEA Technologies in the U.K.; A study of clearance and translocation of aluminum oxide from lungs at the New York Univers
21、ity School of Medicine; Analysis of aluminum in the body and brain at the Universities of Kentuclq and Virginia and the IBR and NIA Laboratories; Analysis of aluminum in body fluids following occupational exposure at the Universities of North Carolina and Pittsburgh; Estimation of dietary intake of
22、aluminum at Hazleton Laboratories and the University of Wisconsin; and Studies of the effects of aluminum on bone at Duke University. In order to encourage open discussion on the subject, the Association sponsored and participated in a number of conferences on aluminum and health. The Association al
23、so sponsored a monograph, “Aluminum and Health - A Critical Review,“ edited by Dr. Hillel Gitelman of the University of North Carolina. Published in 1989, it represented a compendium of what was known about aluminum and its interaction with human biology. In 2000, the Association joined in with the
24、International Aluminium Institute and a number of national aluminum associations to form a Global Health Research Working Committee to fund and provide oversight for needed health studies on an international basis. This paper is an attempt to present for the lay audience a review of the issues and t
25、he efforts by the aluminum industIy to develop a better understanding of the role of aluminum, if any, in the human body. WHAT IS ALUMINUM? Before discussing what is known and not known about aluminum in the body let us consider a more basic question: What is aluminum? To most people, aluminum is a
26、light, silvery metal used to make a variety of products from airplanes and automobiles to pots and pans and baseball bats; nearly everyone uses aluminum foil. However, it is much more than that. Aluminum is a chemical element - one of 90 naturally occurring elements on earth that serve as the buildi
27、ng blocks in nature. As an element, aluminum has unique physical and chemical properties. It is the third most abundant element in nature, representing about eight percent of the earths crust, or surface. Only oxygen and silicon are found in greater quantities (see Table 1). Aluminum is . everywhere
28、; it is present in soils and clays, minerals and rocks and even in water - but not as a metal. TABLE 1 The Twelve Most Abundant Elements in the Earths Crusts PERCENT BY WEIGHT CHEMICAL IN SOLID PORTION OF ELEMENT SYMBOL EARTHS CRUST Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium Tit
29、anium Hydrogen Carbon Chlorine O Si Al Fe Ca Na K Ti H C c1 Mg - 47.3 27.7 7.9 4.5 3.5 2.5 2.5 2.2 0.5 0.2 0.2 o. 1 That is because aluminum is a very chemically active element. Because of its chemical activity, and particularly its affinity for oxygen, aluminum is not found in its free, or metallic
30、, state in nature; indeed, metallic aluminum was unknown until about 150 years ago. Instead, aluminum is always found chemically combined with other elements, particularly oxygen. Just as silicon and oxygen combine to form silica, commonly seen as sand and as quartz in most rocks, aluminum and oxyge
31、n combine to form alumina, commonly found in soil and clay and as the minerals corundum, sapphire and ruby. Bauxite, a clay-like substance that is the principal ore of aluminum, is a combination of alumina, silica and iron oxides. Most elements, including aluminum, have three chemical forms: combine
32、d, ionic and 2 uncombined or “free“. (A few elements are relatively inert and do not readily react with other species.) Aluminum compounds. Aluminum will combine chemically with other elements in fured ratios to form new species called compounds. Compounds have appearance and properties far differen
33、t than the elements comprising them; the elements completely lose their identity when combined in a compound. The classic example is the combination of two reactive gases, hydrogen and oxygen, which combine to form water, a liquid at room temperature. Aluminums favorite “partner“ in such combination
34、s is oxygen, and aluminum will combine with oxygen whenever it is able to do so. Aluminum compounds, and not the metal, are the “natural“ forms of aluminum and the way aluminum is found in nature - not as a metal, but combined with other elements in compounds. Ionic aluminum. While most aluminum com
35、pounds will not dissolve in water, some do. A notable example is aluminum sulfate, commonly known as alum, extensively used in water treatment facilities. In solution, aluminum is released, as a positively charged ion*, from the sulfate portion of the compound. The free aluminum combines with other
36、elements in solution to form new compounds which, if insoluble, precipitate from the solution. Very little aluminum ion is normaily present in neutral (non-acidic and non-alkaline) waters .9 Metallic aluminum. This is the recognizable form of aluminum, although it has only existed in appreciable qua
37、ntities in this form for the past 100 years. The aluminum industry reduces alumina, that is, “frees“ aluminum from oxygen and puts it into its metallic, “useful“ form. Only an infinitesimally small percentage of naturally occurring aluminum has been thus converted. The properties of metallic aluminu
38、m are well known and have been summarized elsewhere.10 Even in its metallic form, however, aluminum remains a chemically active element. Aluminum Oxide. What makes aluminum usable as a metal is that it instantly forms a thin layer of protective oxide by reacting with the oxygen in air.10 Once formed
39、, the oxide adheres tightly to the metal surface and protects it from further oxidation and from attack by other * An atom is the smallest unit of an element; an ion is an atom with a positive or negative charge and can only exist as such in solution, or in the gaseous state. elements. However, the
40、oxide is only stable in a pH range of about 4.5 to 9 (a pH value of 7 is neutral), which means that aluminum is subject to attack by both acids and alkalies. This propem of aluminurn oxide has come to light in the controversies concerning acid rain phenomena. Acid precipitation can break down the al
41、uminum oxide, stable and inert in nature since the dawn of time, and release ionic aluminum from the soil. Once in a body of water, the aluminum will tend to precipitate out of solution as the waters are neutralized. Thus, we see that aluminum can have several forms. However, in foods, in waters and
42、 in the body, it is chemical aluminum - either in compound or ionic form - and not metallic aluminum that is present. In every case when mention is made of the presence of aluminum in the body, it is as chemical aluminum and not the metal - unless, of course, the person mentioned has a medical impla
43、nt for which the metal is used. ALUMINUM IN THE BODY Let us now briefly consider what is known and not known about aluminum in the body - how it gets in, how much typically gets in, and what it does there. Three basic factors will be discussed: Emosure - what are the sources of aluminum to which we
44、are exposed. Absomtion and Metabolism - whether aluminum gets into the body, where it goes and how the body disposes of it. Effects - what medical and biological consequences the element may produce. Figure 1. The Aluminum Cycle 3 Exposure to Aluminum Figure 1 graphically illustrates how aluminum in
45、 the soil is acted upon by natural forces, carried into the air and bodies of water, and enters the food chain. Virtually all foods, water and air contain measurable amounts of the element. Thus it is practically impossible to avoid exposure to aluminum, but the human body appears to have adjusted w
46、ell to its everyday exposures. Table 2 lists the sources of aluminum which might be ingested in everyday circumstances. Estimates are given for the daily amounts of aluminum typically expected from those sources where data are available. The amounts are in milligrams (mg) of aluminum per day (a mill
47、igram is one-thousandth of a gram, and it takes about 28,000 mg to make one ounce). Very little of the ingested aluminum is absorbed, since it is estimated that the adult body contains only about 35 to 40 mg of aluminum.11 TABLE 2 Estimated Daily Intake of Aluminum from Various Sources12 Category So
48、urce Mg Allday FOOD Natural Content 2-10 Intentional Additives 20-50+ (FDA-approved Ai compounds) Unintentional Additives 3.5* (from metallic Ai products) Total Diet: Literature Values 10-100 Greger (1985) 20-40 FDA Study (1989) 9- 14 FDA Study (1995) 7-9 WATER Natural Content, Aium 1-2 AIR Dust, Sm
49、oke, Toiletries, Sprays 1 DRUGS Antacids 50-1000+ Buffered Aspirin 10-loo+ *Maximum value under “worst-case scenario.“ Food The Food and Drug Administration (FDA) publishes a Total Diet Studv which lists 235 foods commonly eaten in the U.S. Using one such list,l3 Dr. Janet Greger, a professor of nutrition at the University of Wisconsin, evaluated the aluminum content of typical American diets. In a published paper,14 she estimated that Americans ingest from three to over 100 mg of aluminum daily, with most adults probably consuming between 20 to 40 mg each day
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