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ORIGINAL ARTICLE
Iron loading in humans: A risk factor for enhanced
morbidity and mortality
E. D. WEINBERG, PhD
Department of Biology and Program in Medical Sciences, Indiana University, Bloomington, IN 47405,
USA
Abstract
Purpose. To develop an overview of the kinds of disease that can be exacerbated by excessive/
misplaced iron; to briefly consider mortality data on iron-loaded persons; and to summarize methods
for the prevention and therapy of iron loading.
Design. Literature review.
Materials and methods. A survey of clinical and research medical journals of the past decade was
carried out. The diseases were categorized by medical specialty and by currently proposed types of
iron association.
Results. A remarkably diverse assemblage of diseases have been reported to be associated with
and/or exacerbated by excessive or misplaced iron in specific tissue sites. Reduced longevity was
associated with iron loading in two studies, but not in a third. Behavioral factors, as well as
genetic modifiers, have been described that can result in an increase in inhaled, ingested and
injected iron.
Conclusions. Our present knowledge strongly indicates that methods for the reduction of iron loading
could contribute considerably to the improved health and longevity of human populations.
Key words: Inhaled iron, iron-associated diseases, iron chelation, iron-enhanced morbidity, iron-
enhanced mortality, iron loading
Introduction
Excessive iron in specific tissue sites promotes infection and neoplasia. Moreover, elevated
iron is also a risk factor for cardiomyopathy, arthropathy, and an array of endocrine,
neurodegenerative and other chronic diseases. The metal, which cannot substantially be
excreted, is hazardous in several ways. Non-protein-bound ferric ions are reduced by
superoxide and the ferrous product is reoxidized by peroxide to regenerate ferric ions and
yield hydroxyl radicals. The latter attack all classes of macromolecules. Hydroxyl radicals
can depolymerize polysaccharides, inactivate enzymes, initiate lipid peroxidation and, not
least, cause DNA strand breaks [1].
Correspondence: E. D. Weinberg, Biology Department, Indiana University, Bloomington, IN 47405, USA. Email: eweinber@
indiana.edu
Journal of Nutritional & Environmental Medicine
February 2007; 16(1): 43–51
ISSN 1359-0847 print/ISSN 1364-6907 online #2007 Informa UK Ltd
DOI: 10.1080/13590840601167685
Furthermore, overabundant iron can serve as a readily available nutrient for invading
neoplastic cells, as well as for bacterial, fungal and protozoan pathogens. Even microbial
strains that are usually not dangerous can cause disease when present in iron-loaded tissues,
fluids or cells [2]. Vertebrate hosts maintain an iron-withholding defense system [3]
designed to prevent the accumulation of non-protein-bound (free) iron in sensitive sites
and to sequester the metal in innocuous packages in ferritin. However, numerous
behavioral factors and genetic modifiers can result in contravention of the iron-withholding
defense system.
Method
A survey of clinical and medical research journals of the past decade was carried out. The
diseases were categorized by medical specialty and by currently proposed types of iron
association.
Iron enhances morbidity
In Table I, iron-associated diseases are grouped by medical specialty. As is evident,
the iron-loaded patient might be diagnosed and treated not only by the family practitioner
but also by a considerable variety of medical specialists. Possible mechanisms whereby
excessive or misplaced iron can initiate or exacerbate a disease are summarized in
Table II.
Diseases can often be subdivided with regard to the initiating condition. For instance,
among established causes of osteoporosis are deficiencies in vitamin D, ascorbic acid or
calcium; hyperparathyroidism; or prolonged therapy with thyroid hormone or steroids [4].
Recently, an additional cause has become well documented, i.e. iron loading. In animal
models and in human patients, iron per se can, by specifically suppressing osteoblast
formation, cause osteoporosis in the absence of the conditions listed above [5]. Indeed the
term ‘siderotic osteoporosis’ might be an appropriate designation. Similarly, the adjective
‘siderotic’ might be applied to a subset of such other diseases as cardiomyopathy and
growth deficiency when, in specific cases, iron is established to be the sole initiator.
Iron enhances mortality
Three studies have presented data on mortality rate in untreated iron-loaded persons.
In one, the percentage of C282Y heterozygote hemochromatotic carriers in a Danish
population of 376 women decreased from 19.5 to 9.9% between age 45 and 74 years;
in 363 men from 12.4 to 8.1% (Table III) [38]. Some, but not all, carriers tend
to acquire excess iron [39]. Unfortunately, in this study, body iron levels were not
ascertained.
In another study [40], in a set of 10,714 US adults, 2.3% had transferrin iron saturation
(Tfsat%) values .55%. During the subsequent 22 years, the rate of mortality of the iron-
loaded group was accelerated (Table IV). Except for a higher amount of diabetes and
hepatic cirrhosis in persons with Tfsat% .55%, the causes of death were similar to those
with Tfsat% ,55%.
In a different study of 41,038 US adults, which included 152 C282Y homozygotes,
selective loss of the latter as the population aged was not observed [41].
44 E. D. Weinberg
Behavioral and genetic factors can increase body iron burden
Examples of behavioral and genetic factors that can enhance body iron loading are listed in
Tables V and VI. Among patients who have a particular factor, there is much variation in
specific tissue sites of iron deposition. Moreover, combinations of factors can result in
synergistic rather than merely additive damage.
Table I. Examples of diseases for which excessive/misplaced iron can be a risk factor.
Cardiovascular
atherosclerosis
cardiomyopathy
hypertension
Dermal
porphyria cutanea tarda
Endocrine
diabetes
growth deficiency
hypogonadism
hypothyroidism
Gastrointestinal
colorectal cancer
Hepatic
cirrhosis
hepatoma
steatohepatitis
viral hepatitis
Infectious
microbial infections of all body systems
Neurologic
ALS
Alzheimer’s
depression
Friedreich’s ataxia
Huntington’s
multiple sclerosis
PKAN
Obstetric
neonatal hemochromatosis
pre-eclampsia
Ophthalmic
macular degeneration
Orthopedic
gout
hemophilic synovitis
osteoarthritis
osteoporosis
Otologic and Renal
aminoglycoside toxicity
Pediatric & Neonatal
Down syndrome
epilepsy
sudden infant death
Pulmonary
cystic fibrosis
lung cancer
pneumoconiosis
Iron-associated morbidity and mortality 45
For example, in a group of 3410 US adults, 27.3% had serum levels of low-density
lipoprotein (LDL) .160 mg dl
21
and 1.64% had Tfsat% .55% [42]. If only LDL or
Tfsat% was elevated, the relative risk of dying with atherosclerosis was 1.4 or 1.57,
respectively. However, if both factors were high, the relative risk was 5.21. An animal
model has confirmed this observation. Rabbits with both hypercholesterolemia and an
Table II. Examples of mechanisms of iron-associated disease.
Iron, by itself, has been observed to initiate:
cardiomyopathy [6]
growth deficiency [7]
hemophilic synovitis [8]
hypogonadism [9]
lung cancer [10]
osteoporosis [5]
pneumoconiosis [11]
Iron can be a cofactor in promoting:
Alzheimer’s disease [12]
bacterial infections [13]
diabetes [14]
fungal infections [15]
gout [16]
hepatoma [17]
multiple sclerosis [18]
protozoan infections [15]
osteoarthritis [19]
oto- and renal toxicity [20]
Iron deposits are observed in disease-associated tissue sites:
basal ganglia in Hallervorden–Spatz (PKAN) disease [21]
hepatocytes in viral- and steato-hepatitis [22,23]
retina in macular degeneration [24]
mitochondria in Friedreich’s ataxia [25]
pulmonary secretions in cystic fibrosis [26]
substantia nigra in Parkinson’s disease [27]
Body iron loading is associated with above-normal incidence of:
amyotrophic lateral sclerosis [28]
atherosclerosis [29]
colorectal cancer [30]
Down syndrome [31]
epilepsy [32]
hypertension [33]
pre-eclampsia [34]
porphyria cutanea tarda [35]
sudden infant death syndrome [36]
Maternal antibodies can impair fetal iron metabolism
fetal or neonatal death in neonatal hemochromatosis [37]
Table III. Decline in frequency of C282Y carriers with age.
45–54 years 55–64 years 65–74 years
Number %C282Y Number %C282Y Number %C282Y
Women 200 19.5 85 17.6 91 9.9
Men 161 12.4 91 8.8 111 8.1
Data from Table 2 in [38].
46 E. D. Weinberg
elevated iron level had significantly more aortic atherosclerosis than rabbits that were above
normal in either one of the two factors [43].
Nevertheless, in patients with a common cause of iron loading, i.e. hemochromatosis, the
incidence of atherosclerosis uniquely is not raised [44]. A possible reason for this anomaly
Table IV. Enhanced mortality associated with elevated transferrin iron saturation (Tfsat).
Time (years) after initial transferrin test
Mortality (%)
Tfsat ,55% Tfsat .55%
225
4 3.5 6
6 5.5 13
8816
10 10 19
12 13 24
14 16 27
16 20 32
18 23 33
20 25.5 34
22 26.5 36
The initial population was comprised of American adults aged 24–74 years: 10,468 had Tfsat ,55%; 246 had
Tfsat .55%. Data from Figure 1 in [40].
Table V. Behavioral factors that enhance body iron loading.
Inhalation
Mining: iron; iron-contaminated coal or sand; iron silicates in amosite, crocidolite or tremolite asbestos
Processing: steel grinding or polishing; asbestos in building materials
Painting: iron silicate in tremolite
Smoking: iron-contaminated tobacco smoke
Urban habitation: iron-contaminated urban and subway air particulates
Ingestion
Iron additives in processed foods
Iron supplements
Heme iron in red meats
Ascorbic acid supplements consumed with iron-containing items
Ethanol consumed with iron-containing items
Injection
Iron saccharates
Erythrocytes or whole blood
Table VI. Examples of genetic disorders associated with body iron loading.
Enhancement of intestinal absorption of ingested iron
Aceruloplasminemia
African siderosis
Juvenile or adult hemochromatosis
Thalassemia
Requirement for periodic blood transfusions
Myelodysplasia
Sicklemia
Thalassemia
Iron-associated morbidity and mortality 47
is that, in this specific iron disorder, macrophage iron remains low, apparently due to a lack
of hepcidin. For the development of atherosclerosis, iron-rich macrophages are considered
to be important components [45].
The oxidative role of iron in lipid peroxidation may be critical, not only in the
development of atherosclerosis, but also in such neurodegenerative conditions as
Alzheimer’s disease [27]. Oxidized LDL induces neuronal cell death [46]. In a group of
6558 US adults aged .40 years, followed for 20 years, the relative risk of developing
Alzheimer’s disease when both total cholesterol and Tfsat% were at the 75th percentile was
3.19 [47]. When only one of the factors was elevated, there was no increased risk for
Alzheimer’s disease.
Prevention of iron loading
All persons, not only those with mutations that enhance body iron loading, should
minimize as much as possible the behavioral factors listed in Table V. Industrial workers
exposed to airborne iron should be advised to wear masks. Their on-the-job clothing should
be carefully laundered to prevent their families or laundry workers from being exposed to
iron dust. Home owners should be warned against applying tremolite paint to the inner and
outer walls of their houses [48]. Curtailment of active and passive inhalation of tobacco
smoke is essential for the prevention of iron toxicity to respiratory tract tissue [10].
Persons whose diets include high amounts of non-heme iron can lower the quantity
absorbed by concurrent consumption of the natural phenolic iron chelators in tea [49] and
of phytates in whole grains [50]. A reduction in heme iron intake can be achieved by
lowering the ingestion of red meat [50]. Men of all ages, as well as post-menopausal
women, should consider periodic donations of blood; each unit drawn results in a reduction
in the iron burden of 250 mg [51].
An increasingly large number of clinical reports on the hazards of iron loading continue
to emphasize the necessity of including the Tfsat% level in routine biochemical profiles of
adults of all ages. Individuals with high iron values should be counseled to take prompt
action. Just as persons predisposed to hypertension or hypercholesterolemia are urged to
take hypotensive or cholesterol-lowering drugs, respectively, while their cardiovascular
system has not yet become damaged, so must hyperferremic persons be urged to lower their
iron burden while their general health has not yet been compromised.
Therapy of iron loading
In hemochromatosis, hemoglobin is normal; thus blood transfusions are not required and
iron loading can be treated appropriately by phlebotomies. In contrast, in hemoglobino-
pathies, such as thalassemia and sicklemia, as well as in myelodysplasia, specific iron-
chelating drugs must be administered to reduce the transfusion-associated iron burden.
Presently in most countries, subcutaneous deferoxamine (DF), oral deferiprone (DP) and
their combinations are the established iron-chelating drugs [52]. A combination of DP
during the day and DF at least three nights per week can achieve a negative iron balance
and the clearance of cardiac iron.
A more recently developed oral iron chelator, deferasirox, is in clinical trials. Combinations
of DF or DP with deferasirox may be necessary to increase the ability of the latter to maintain a
negative iron balance and cardiac iron clearance [52]. Among other iron chelators in
preliminary stages of development are deferitrin, L1NA11, and starch DF polymers.
48 E. D. Weinberg
Two natural product protein iron chelators, transferrin and lactoferrin, are becoming
available for therapy of iron loading at specific sites. Transferrin has been extracted from
human serum, de-ironed and purified [53]. The product is employed in conditions in
which iron saturation of the patient’s transferrin has become highly elevated. Moreover, in
pre-term infants, such oxygen radical injury as retinopathy and bronchopulmonary
dysplasia might be alleviated by the injection of apotransferrin [54].
Recombinant human lactoferrin is produced in molds as well as in cells of plants and
animals [55]. Another source of the protein is bovine lactoferrin extracted from cow’s milk.
Lactoferrin is being tested/employed in a considerable diversity of nutraceutical,
preservative and pharmaceutical applications. In most, but not all, the mechanism of
action of lactoferrin is considered to be that of iron chelation.
Acknowledgment
This review is dedicated to Gu¨ nter Weiss, MD, in recognition of his fundamental research
on the anemia of chronic disease.
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Iron-associated morbidity and mortality 51