characterized by deposits of iron compounds in organs such as the liver
and heart. Acute ingestion of large doses of ferrous salts can be fatal,
particularly in children under the age of two. Manganese deficiency is rare
but is believed to cause ataxia, hearing loss and dizziness. Inhalation of dust
from mining and other industrial sources can lead to manganese toxicity
and causes severe neurological dysfunction, similar to Parkinson’s disease
(Chapter 18). A dietary deficiency of molybdenum has not been reported.
However, molybdenum deficiency was noted in a patient on parenteral
nutrition who suffered from mental disturbances that progressed to coma.
Supplementation of molybdenum improved the patient’s clinical condition.
Levels of manganese in food and water must exceed 100 mg kg–1 body
weight to produce manganese toxicity. However, few data are available but
the major signs include diarrhea and anemia. The high concentrations are
thought to stimulate xanthine oxidase, leading to increased serum uric acid
and gout (Chapter 8).
Selenium deficiency results from a low dietary intake in parts of the world with
soils of low selenium content and has been reported in patients on long-term
parenteral nutrition. A deficiency of selenium may lead to a cardiomyopathy.
In China, this is called Keshan’s disease and affects young women and children
in selenium deficient regions and although selenium deficiency is a basic
factor in Keshan’s disease, its occurrence is seasonal and it is associated with
viral infections that cause inflammation of the heart. Prophylactic selenium
prevents the disease developing but selenium supplements do not reverse
heart muscle damage. A large intake of selenium causes selenosis, a condition
characterized by loss of hair, skin and nails.
Zinc deficiency is relatively common in populations in rural areas of the
Middle East and subtropical and tropical areas where unleavened whole
wheat bread can provide up to 75% of the energy intake. The little zinc in
wheat is bound by the relatively large amounts of phytic acid and fiber present
that inhibit its absorption. This is not a problem in leavened bread, as yeasts
produce phytases that inactivate the phytic acid. Zinc deficiency also occurs
during prolonged parenteral nutrition if inadequate amounts are provided.
A deficiency is associated with a period of severe catabolism, as would occur
in PEM. A severe deficiency occurs in the skin condition acrodermatitis
enteropathica, where there is an inherited defect in GIT zinc absorption. A
deficiency of zinc delays the onset of puberty. High doses of zinc reduce the
amount of copper the body can absorb causing anemia and weakness of the
bones.
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caries than those in areas where the water fluoride was below
0.1 ppm. Indeed, removal of fluoride from the water increased
the incidence of caries. These UK studies have been supported
by others worldwide, where similar results have been obtained
despite ethnic, social, climatic and dietary differences. Fluoride
in toothpastes, mouthwashes or when consumed in a liquid
or tablet form is also effective in preventing dental caries. The
addition of fluoride to drinking water at concentrations greater
than 12 ppm promotes dental fluorosis, a mottling of the teeth
as they form in the jaws. Its effects are generally cosmetic and
only cause functional problems when the disorder is severe.
Other concerns of fluoridation include its possible association
with cancer and arthritis. There is, however, a weak association
between fluoridation and an increased susceptibility to bone
fractures.The addition of fluoride to drinking water has also raised ethical
issues because it is seen by some as an infringement of personal
liberty in that individuals have no choice but to drink water
containing fluoride. The use of fluoridation requires careful
consideration of the ethical issues and the balance between its
beneficial and any potentially harmful effects.