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Selenium in food and human health

Date:2016-12-11 12:27:17    Visit:497

Selenium is a contradictory nutrient. It has been called the essential poison—too much of it  in the diet can be toxic; too little can result in chronic, and sometimes
fatal, deficiency. Even health authorities have at times been confused. Although
today in the USA, as in most other countries, selenium appears among the trace
elements for which recommended dietary allowances (RDAs) have been estab-
lished, it was at one time declared by the Food and Drug Administration (FDA)
to be a carcinogen and banned as an additive in food.
Selenium is considered by some to be a serious hazard to the environment and
to animal health. Selenium-contaminated water has brought deformity and death
to wildlife in nature reserves in western USA. There is even concern that because
of selenium contamination of soil, crops supplied to the great cities of California
could become unfit for human consumption. In large areas of China, endemic
selenium toxicity is a hazard for locals who depend on crops grown on selenium-
rich soil. Yet, in the UK, and in other parts of Europe, fears are expressed that soil
selenium levels are inadequate. There are demands that the example of Finland
should be followed and soil selenium levels increased by the addition of selenium
to fertilizers.
There may be controversy among the experts and health authorities about sele-
nium, but this has not deterred the general public from deciding that the element
has an important role to play in health. In New Zealand, when the use of selenium
was first permitted to prevent deficiency in farm animals, but was still not
approved as a supplement for humans, people took the matter into their own
hands. Veterinary preparations containing selenium were used by those who
believed that what was good for animals must also be good for humans.
Undeterred by reports of their possible toxic effects, today millions of people
worldwide consume selenium supplements. They are encouraged to do so, not
only by articles in the popular media but also by the results of investigations by
reputable scientists which indicate that selenium has a vital role to play in human
health, not least in the prevention of cancer. Their findings indicate that selenium
is a key player in cellular metabolism, is an essential component of enzymes that
protect the body against oxidative damage, and has important roles in thyroid
metabolism, human fertility, and many other vital functions.

But not all the experts are convinced by such findings. They point out that there
is still a great deal we do not know about selenium and its relation to body func-
tion and human health. They argue that not all the evidence supports the claims,
for instance, of selenium’s anticancer role. It must not be forgotten, they point
out, that selenium is both a toxic and an essential element and that the difference
between the two is measured in minute amounts.
Thus, though selenium is probably the most widely investigated of all the
trace element nutrients, it continues to be highly controversial. Indeed, it has
been so all through the nearly 200 years since it was first identified by the
Swedish scientist, J ns Jakob Berzelius. He named his new discovery selenium
after the moon goddess, Seleˉneˉ—an appropriate name, since, like the moon, the
element has two faces—dark and light, good and bad. It is because of the inter-
actions of those opposing faces that selenium remains a controversial topic to the
present day.
It has been estimated that more than 100,000 scientific papers, not to mention
popular articles and books, about selenium have been published over the past 50
years. These publications continue to appear without showing any sign of diminu-
tion today. This mass of writing makes it very difficult for anyone who is not a
dedicated and specialized scientist to get a clear picture of what is now known
about the element and its role in human health. Not only for the general reader
who wants to make an informed judgment about the competing claims for and
against its value as a nutritional supplement, but even for some professionals who
want to keep abreast of the latest findings about its potential role in the manage-
ment of human health, this is a serious deterrent to their quest for knowledge.
The first edition of this book was written with the intention of providing reli-
able and up-to-date information to readers who wanted to learn more about sele-
nium, but who were deterred by either a lack of time or, they believed, by their
inadequate scientific background, from wading through the extensive literature
then available. Its aim was to present, in a readable and user-friendly manner, a
review, based on a wide range of scientific and other literature. It would, it was
hoped, provide all that was essential for readers who wanted to know more about
selenium, as a component of food and diet, its biological significance, and its role
in health and disease.
Ten years later, this new edition of Selenium in Food and Health is written with
the same aim, to provide readers with a clear and reliable account of the extraor-
dinary story of selenium and its role in human health. It is based on the author’s
more than 3 decades of teaching undergraduate and graduate students about trace
elements and his active participation in selenium research, as well as on extensive
reading of the pertinent literature and information gathering at workshops and
conferences in many different countries.
This new edition takes into account the considerable amount of fresh informa-
tion that has been published over the past decade, by investigators from a wide
range of specialisms, not all of which might at first glance appear to have much
to do with human health. For readers who have the background to do so, and are
willing to search further, many references to original and up-to-date reports and
reviews in the scientific literature are provided. The book will not tell the final
story—much is still to be discovered. Even as I write, new findings are being
reported and new discoveries about selenium are being made, especially as mod-
ern bioinformatics and genetic techniques are brought to bear. It is hoped that
what has been produced will help to make the picture clear and help readers to
form their own, informed, opinion about the importance of selenium in human
food and health, and that the text is readable and comprehensible, bringing clar-
ity without distortion or oversimplification. It is intended for a wide audience,
including dietitians, nutritionists, and other health professionals, food scientists,
medical practitioners, and, not least, general readers who want to learn about the
element that is so often in the news.
This book is dedicated to the memory of my late wife, Ann, who not only
encouraged me to write but also took part in some of the research on which it is
based, and also in the days when literature searches required more than sitting at
a computer keyboard, spent long hours reference checking in the library stacks.
The book owes much to the generous help of the library staff of the Queensland
University of Technology, especially to the wonders of the Internet that allowed
me to access journals and other publications in the library’s databases, even when
I was more than 12,000 miles away from the antipodes. I also thank the staff of
the Bodleian Library of Oxford University, where I had the special pleasure of
being able to read, in the original, the earliest of the publications on selenium,
including the key paper in which Berzelius announced, in 1818, his discovery of
the element.
Gratitude is due also to others who contributed to the writing of the book.
I thank several of my academic colleagues and friends in many countries, in par-
ticular Dr. Fiona Cumming and Dr. Ujang Tinggi, Professor John Arthur,
Professor Jim Oldfield, Dr. Margaret Rayman, and several others who prefer to
be nameless. They helped in different ways, by taking part in my research activ-
ities, supplying copies of their publications, discussing my ideas, and in some
cases reading and commenting on sections of the text. The views expressed in this
book, however, are solely mine and do not necessarily reflect their opinions.
Conor Reilly
Enstone, Oxfordshire, UK
58棋牌January 31, 2006

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