Vitamin E deficiency

Vitamin E defi ciency
9.8.1 Defi ciency in animals
Vitamin E defi ciency in animals is readily demonstrable
and results in a variety of pathological conditions
that affect the muscular, cardiovascular, reproductive
and central nervous systems as well as the liver, kidney
and erythrocytes. There is a marked difference between
animal species in their susceptibility to different
defi ciency disorders. A complex biochemical interrelationship
exists between vitamin E and the trace element
selenium. Unsaturated fat, sulphur-containing
amino acids and synthetic fat-soluble antioxidants are
also implicated in some disorders. Consequently, in
order to experimentally induce a particular defi ciency
syndrome in a given species, it is usually necessary to
adjust the balance of these nutrients in the diet. The
most extensively studied defi ciency syndromes are
listed in Table 9.3.
Fetal resorption
In female rats deprived of vitamin E all reproductive
events are normal up to implantation of the fertilized
ova. Several days later, however, the developing fetus
shows abnormalities followed by intra-uterine death,
rapid autolysis and resorption. A defect in the fetal
blood vessels may be the primary event leading to
death of the fetus (Nelson, 1980). This disease can
be prevented by administering an adequate dose of
vitamin E as late as the tenth day of pregnancy. The
synthetic antioxidant DPPD is at least as effective
as α-tocopherol in preventing fetal resorption, but
ethoxyquin, which readily prevents encephalomalacia
in chicks, is inactive (Draper et al., 1964). Selenium
compounds have no effect on fetal resorption in rats.
Erythrocyte haemolysis
Erythrocyte plasma membranes are particularly vulnerable
to lipid peroxidation because of their direct
exposure to molecular oxygen and the presence of
haemoproteins which are catalysts of peroxidation.
Erythrocytes isolated from blood samples of vitamin
E-depleted rats exhibit spontaneous haemolysis when
added to dilute solutions of dialuric acid, whereas
erythrocytes of rats receiving vitamin E are resistant
to this haemolysis. This early manifestation of vitamin
E defi ciency can be prevented by certain synthetic
antioxidants administered to the animal or added to
the cell suspension in vitro as well as by vitamin E.
Selenium compounds have no effect on erythrocyte
haemolysis.
Encephalomalacia
This nutritional disorder occurs in growing chicks
fed vitamin E-defi cient diets containing adequate
amounts of selenium for the prevention of exudative
diathesis and suffi cient methionine or cystine for the
prevention of necrotizing myopathy. Encephalomalacia
is manifested by lesions of the cerebellum, the part
of the brain concerned with coordination of movement.
The cerebellum is softened, swollen and oedematous
with minute haemorrhages on the surface and
greenish-yellow necrotic areas. The necrosis may be
the result of thrombosis in the capillaries. Once established,
the lesions are irreversible. The main symptoms
are ataxia of gait and stance, backward or downward
retraction of the head, tremors, spasms of the
limb muscles, and eventually prostration, stupor and
death within a few hours. The incidence and severity
of the disease are markedly increased with increasing
levels of linoleic acid in the diet. Low concentrations
of synthetic antioxidants such as DPPD and ethoxyquin
in the diet readily prevent encephalomalacia, but
selenium has no effect.
Exudative diathesis
This is a vascular disease of chicks which develops
as a result of feeding diets that are low in both vitamin
E and selenium. The disease can be induced
for experimental purposes by feeding diets based on
Torula yeast, which is low in both micronutrients and
contains substantial amounts of unsaturated fatty
acids. The most obvious manifestation is a massive
accumulation of a greenish fl uid under the skin of the
breast and abdomen. Internally, the oedema extends
to the muscles and many organs, including the heart
and lungs. The oedema is the result of a leakage of
plasma from the capillaries caused by an increased
permeability of the capillary walls. The disease can
be prevented by administration of either vitamin E
or selenium, provided that the selenium defi ciency is
not too severe (Thompson & Scott, 1969). A severe
defi ciency of selenium causes degeneration of the
exocrine component of the pancreas and consequent
impairment of dietary lipid absorption, which will
affect the absorption of vitamin E (Thompson &
Scott, 1970). In this event, extremely high doses of
vitamin E are required to prevent exudative diathesis.
Some synthetic antioxidants, including DPPD and
ethoxyquin, are also effective, but only at concentrations
distinctly greater than those required to prevent
encephalomalacia.
Liver necrosis
Necrotic liver degeneration develops in weanling rats
after commencement of a diet based on Torula yeast,
which is defi cient in both vitamin E and selenium and
low in sulphur-containing amino acids. Necrosis is
preceded by degeneration of the sinusoidal cellular
plasma membrane and lipid peroxidation has been
detected late in the progress of the disease. The onset
of necrosis is delayed by cystine, which appears to have
a sparing action on the amount of vitamin E or selenium
required to prevent the disease.
Testicular atrophy
In male rats depleted of vitamin E from early life there
is no testicular injury until the onset of sexual maturity,
when a progressive degeneration of the germinal
epithelium of the seminiferous tubules occurs and the
testes atrophy. The resultant sterility does not respond
to vitamin E and is truly permanent.
Necrotizing myopathy
This disease is manifested as a progressive muscular
weakness which affects the skeletal muscles of many
vertebrate species. It was originally called nutritional
muscular dystrophy, but this term suggests an aetiological
relationship between the myopathy of vitamin
E defi ciency and human muscular dystrophy. Although
many of the pathological lesions are similar
in these two diseases, human muscular dystrophy is
genetically determined and does not respond to vitamin
E treatment.
Necrotizing myopathy is characterized histologically
by marked variation in the cross-sectional
diameter of the muscle fi bres, segmental fragmentation
with interstitial oedema and necrosis and, in the
later stages, extensive replacement of muscle tissue by
connective tissue. The disease can be detected in its
early stages by an increased excretion of creatine in
the urine (creatinuria), which is the result of a loss of
creatine from the affected muscles. Creatine excretion
is often expressed as the creatine:creatinine ratio, the
excretion of creatinine being relatively constant on a
body weight basis.
Necrotizing myopathy in rabbits, guinea pigs, rats
and monkeys responds primarily to vitamin E. Selenium
is not capable of completely replacing vitamin
E in these species, although it does reduce the vitamin
requirement. The myopathy, as studied in the chick,
does not respond to dietary synthetic antioxidants at
levels several times those needed to prevent encephalomalacia.
The disease is induced in the chick when
the dietary vitamin E is accompanied by a defi ciency
in the sulphur-containing amino acids, methionine
and cystine. Approximately 0.5% of dietary linoleic
acid (but not linolenic acid) is necessary to produce
myopathy. Concentrations above 0.5% do not increase
the amount of vitamin E required for preven-
Vitamin E 249
tion. The chick appears to be unique in that the myopathy
can be prevented in the absence of vitamin E
by supplementing the diet with cystine or methionine.
Cystine is about twice as effective as methionine on an
equal sulphur basis (Scott, 1970).
9.8.2 Defi ciency in humans
Apart from haemolytic anaemia in premature infants,
vitamin E, in the context of human nutrition,
has long been considered ‘a vitamin looking for a
disease’. It is now recognized that vitamin E is responsible
for the neurological abnormalities that had
been described in patients with long-term disorders
of fat absorption.
Haemolytic anaemia
Newborn infants generally have low serum vitamin
E levels because of the vitamin’s limited transfer
through the placenta. A haemolytic anaemia associated
with vitamin E defi ciency in premature infants
6 to 10 weeks after birth was fi rst reported by Oski &
Barness (1967). This defi ciency syndrome was further
investigated in infants fed commercial milk formulas
that were high in PUFA and relatively low in vitamin
E (Hassan et al., 1966; Ritchie et al., 1968). Control infants
were fed identical formulas supplemented with
vitamin E. The syndrome consisted of haemolytic
anaemia, oedema and skin lesions. The erythrocytes
lysed when treated in vitro with dilute hydrogen peroxide
(i.e. the cell contents leaked out of the damaged
cell membrane) and the blood fi lm showed abnormal
red cell morphology, such as spiky and fragmented
cells. Erythrocyte survival was shortened and an
increase in the number of reticulocytes (erythrocyte
precursors newly arrived in the blood from the bone
marrow) indicated a response to increased erythrocyte
destruction. Erythroid hyperplasia was observed
in the bone marrow and an increased platelet count
was indicative of a general increase in bone-marrow
activity. The infants were restless, breathing was noisy
and there was a watery nasal discharge. Oedema appeared
and slowly progressed until it involved the
entire face, lower limbs and genitalia. The oedema is
analogous to the exudative diathesis observed in vitamin
E-defi cient chicks. The skin lesions began on the
sides of the face extending into the neck and adjacent
parts of the scalp. All of the symptoms were associated
with low serum vitamin E levels; the symptoms
were not observed in the controls, which had higher
serum vitamin E levels. The symptoms disappeared
in response to oral vitamin E therapy; there was no
response to iron or vitamin B12. The lengthening of
erythrocyte survival coincident with the rise in serum
vitamin E was direct in vivo evidence that vitamin E
prevented haemolytic anaemia. The therapeutic effect
of vitamin E in these experiments is presumably
attributable to its ability to protect the vital phospholipids
in cell membranes from peroxidative degeneration.
Nowadays, infant milk formulas contain
added vitamin E and an adequate ratio of vitamin E to
PUFA; this has almost completely eradicated haemolytic
anaemia.
It is well documented that a diet rich in polyunsaturated
fat, but which does not contain a correspondingly
high amount of vitamin E, induces defi ciency
signs in animals. This also applies to humans as shown
by the above experiments with premature infants. In
a long-term human study (the Elgin project), adult
male volunteers received a diet in which about half of
the fat content was composed of vitamin E-stripped
lard. After 30 months this fraction of the fat content
was replaced by stripped corn oil and 9 months later
the amount of stripped corn oil was doubled. No
manifestations of anaemia were observed and it was
not until the 72nd month that a well-controlled study
of erythrocyte survival was performed. The data obtained
showed that the erythrocytes of the vitamin
E-depleted subjects were being destroyed at a rate
about 8–10% faster than in the subjects in the control
groups. The experiment was terminated soon after
these observations, but it is logical to assume that if
the diet had been made more defi cient, the pathology
would have been more severe (Horwitt, 1976).
Fat malabsorption
Because of the intimate association between intestinal
absorption of dietary fat and vitamin E, any condition
causing the prolonged malabsorption of fat (steatorrhoea)
will lead to a secondary defi ciency of vitamin
E. Thus, patients with a variety of chronic fat malabsorption
conditions exhibit low plasma vitamin E
concentrations. The major nongenetic causes of
steatorrhoea associated with a symptomatic vitamin
E defi ciency state are chronic cholestatic hepatobiliary
disorders, cystic fi brosis and short bowel syndrome.
Abetalipoproteinaemia and homozygous hypobetalipoproteinaemia
are genetic causes of steatorrhoea.
250 Vitamins: their role in the human body
Chronic cholestatic hepatobiliary disorders
These disorders include diseases of the liver and of
the intrahepatic and extrahepatic bile ducts. The
impaired bile fl ow leads to an insuffi cient concentration
of bile constituents in the intestinal lumen and
a consequent failure to produce micelles. The result
is malabsorption of dietary fat-soluble substances.
Because of their low vitamin E body stores, infants
with cholestatic liver disease show symptoms of
neuropathy as early as the second year of life, the
neurological damage becoming irreversible if the
vitamin E defi ciency is not corrected. Correction of
the defi ciency by oral administration requires very
high doses of vitamin E (100–200 IU per kg per day)
or the use of a water-soluble form (α-tocopheryl polyethylene
glycol-1000 succinate) which forms micelles.
Alternatively, vitamin E can be administered by intramuscular
injection.
Cystic fi brosis
In cystic fi brosis, increased viscosity of pancreatic
secretions causes obstruction of pancreatic ducts
leading ultimately to destruction and fi brosis of the
exocrine pancreas. The resultant failure to secrete
pancreatic digestive enzymes causes steatorrhoea and
vitamin E defi ciency. Despite the common observation
of neuroaxonal lesions in the posterior column
of the spinal cord at autopsy, overt neurological dysfunction
is rare in vitamin E-defi cient cystic fi brosis
patients. Most patients who do exhibit neurological
dysfunction also have fi brotic livers.
Short bowel syndrome
Short bowel syndrome is a collection of signs and
symptoms used to describe the nutritional consequences
of major surgical resections of the small
intestine. Resections are carried out for treatment of
Crohn’s disease and mesenteric vascular thrombosis,
among other disorders. The causes of vitamin E defi
ciency in these conditions are a reduced intestinal
absorptive surface area and excessive faecal bile acid
losses. Although low plasma vitamin E concentrations
may be present within several years of surgical resection,
10 to 20 years of severe malabsorption are generally
required before the manifestation of neurological
symptoms. This is because of the prior accumulation
of vitamin E in most tissues and its relatively slow release
from nervous tissues.
Abetalipoproteinaemia
Chylomicrons contain apoB-48, among other apoproteins,
while VLDL and LDL contain apoB-100.
These two apoB proteins are encoded by the same
gene, apoB-48 being synthesized in the intestinal
mucosa and apoB-100 in the liver. Abetalipoproteinaemia
is a rare inborn error of lipoprotein production
and transport characterized by undetectable or very
small amounts of apoB-containing lipoproteins (chylomicrons,
VLDL and LDL) in the circulation. The
underlying genetic defect in abetalipoproteinaemia
is a mutation in the gene coding for the microsomal
triglyceride-transfer protein. This protein is essential
for lipoprotein assembly in the Golgi apparatus; without
it the lipoproteins are not secreted by the intestine
or liver. Abetalipoproteinaemia patients become
vitamin E defi cient because the steatorrhoea caused
by the absence of chylomicrons severely impairs
absorption of the vitamin. Furthermore, the lack of
VLDL secretion by the liver means that no LDL can
be formed, and so any vitamin E that might have been
absorbed cannot be transported in the usual manner.
The treatment of abetalipoproteinaemic patients
with massive oral doses of vitamin E (100 IU per kg
per day) allows a small proportion to be absorbed,
resulting in detectable plasma levels and correction of
in vitro erythrocyte haemolysis (Traber et al., 1993).
Normal plasma levels are rarely, if ever, attained. Interestingly,
the enterocytes of abetalipoproteinaemic
patients are able to synthesize HDL, which do not
require apoB for their formation (Deckelbaum et al.,
1982). It is possible that this abnormally produced
enteric HDL facilitates the intestinal secretion and
plasma transport of vitamin E in the absence of the
apoB-containing lipoproteins. The principal clinical
features of abetalipoproteinaemia are steatorrhoea
and spiky erythrocytes (both congenital), pigmented
retinopathy and a chronic progressive neurological
disorder. The characteristic neurological and retinal
symptoms manifest in the fi rst decade of life, evolving
into a crippling ataxia with visual impairment by the
second or third decades (Sokol, 1989).
Homozygous hypobetalipoproteinaemia
Patients with this condition have a defect in the
apoB gene and secrete lipoproteins containing truncated
forms of apoB. These defective lipoproteins can
transport minor amounts of vitamin E but they have
Vitamin E 251
a rapid turnover and constitute only a tiny fraction of
the circulating lipoproteins in these patients.
Ataxia with vitamin E defi ciency (AVED)
Ataxia with vitamin E defi ciency (AVED) uniquely
represents a primary vitamin E-defi cient state.
Originally called ‘isolated vitamin E defi ciency syndrome’,
and later ‘familial isolated vitamin E’ (FIVE)
defi ciency, AVED is the result of a mutation in the
gene for α-tocopherol transfer protein (α-TTP) on
chromosome 8. Infants born with this syndrome have
normal gastrointestinal function and yet their plasma
vitamin E levels are only 1% of normal. There is either
a complete absence of α-TTP or a defect in the
α-tocopherol-binding region of the protein (Traber,
1994); in either case, there is impaired hepatic secretion
of α-tocopherol in VLDL. The dramatic fall in the
plasma level of vitamin E is due to the rapid removal of
α-tocopherol from the plasma to the liver and excretion
in the bile, with no α-TTP to salvage it. The ataxia
and other neurological symptoms appear between the
ages of 4 and 18 years. They are manifestations of the
neurological damage that arises from the impaired
delivery of vitamin E to the nervous tissues, which are
especially sensitive to variations in plasma vitamin E.
When given vitamin E supplements (about 1 g per
day), patients maintain normal plasma α-tocopherol
concentrations and progression of the neurological
damage is halted. If patients stop taking the supplements,
their plasma concentrations fall to defi ciency
levels within days and the damage progresses.
Clinical features and histopathology of vitamin E
defi ciency
Sokol (1988) compared the clinical features found in
abetalipoproteinaemia, chronic childhood cholestasis,
other fat malabsorption disorders and isolated
vitamin E defi ciency (now known as AVED). The
most common fi ndings include loss of deep tendon
refl exes, truncal and limb ataxia, loss of positional and
vibratory sensation, muscle weakness and dysarthria.
Ophthalmoplegia (impairment of eye movements)
and pigmented retinopathy are common features in
abetalipoproteinaemia, cholestasis and other fat malabsorption
disorders, but they are not seen in AVED. A
possible explanation is the fact that the fi rst three disorders
represent secondary defi ciency states, malabsorption
being the primary cause. In contrast, AVED,
with no evidence of fat malabsorption or of other
nutritional defi ciencies, represents a primary defi -
ciency state. A concomitant defi ciency of vitamin A
is probably required to produce the ocular symptoms
present in cases of secondary vitamin E defi ciency, the
two vitamins acting synergistically.
Sokol (1988) also described the histopathology of
vitamin E defi ciency in humans. Axonal degeneration
and demyelination of large-calibre neurons are
universal in both primary and secondary advanced
defi ciency. Disturbance in function of the posterior
columns of the spinal cord, sensory nerves and
spinocerebellar tracts account for the loss of vibratory
and positional sensation and truncal and limb ataxia.
The nerve degeneration presumably originates from
peroxidation of constituent phospholipids. Peroxidative
injury and the formation of lipopigments is the
cause of pigmented retinopathy commonly seen in
older patients with abetalipoproteinaemia.