Download Inorganic nutrients (minerals)

Food sources of
vitamin C
Blackcurrants
Guavas
n Rosehip syrup
n Green peppers
n Oranges and other
citrus fruits
n Strawberries
n Cruciferous plants, eg,
cauliflower, broccoli
cabbage
n Watercress
n Potatoes
n Liver and milk
Figure 2: Synthesis of active vitamin D from dehydrocholesterol
n
n
7-Dehydrocholesterol (Skin)
UV light
Previtamin D
Vitamin D
Dehydrocholesterol is a
companion of cholesterol in
the skin and is changed by
UV light to cholecalciferol
(vitamin D3), the natural vitamin.
The major form in the
blood (measured for diagnosis) is 25-hydroxyvitamin
D [25(OH)-vitamin D],
produced in the liver. This
is converted in healthy kidneys to small amounts of
1,25-dihydroxy vitamin D
[1,25(OH)2-vitamin D (calcitriol)], the active form of
the vitamin (figure 2).
Vitamin D level should
therefore be monitored in
people with liver disease or
renal failure.
The metabolic bone disease in chronic renal failure
is due to lack of 1,25-vitamin D. This form acts on a
specific vitamin D receptor
in the cell nucleus, which
switches on the gene that
induces synthesis of a calcium transport protein (calbindin) in the epithelium of
the small intestine and also
in bone cells.
Not so long ago nutritional opinion was that
Australians get plenty of
sun and, except for our
Warmth
Vitamin D3
Liver
25-hydroxyvitamin D3
(Circulates in the blood)
Kidneys
Sun exposure can be less
in today’s Australians than
often assumed — more
people wear hats, use sunscreen and avoid the sun to
prevent skin cancer, and skin
synthesis of vitamin D is less
efficient in dark-skinned and
older people.
It is likely that subclinical
vitamin D deficiency contributes to osteoporosis as
well as osteomalacia. In addition, breast, colon, prostate
and ovarian cancers are less
common at the sunniest latitudes in the world and there
is laboratory evidence that
vitamin D promotes differentiation in these cells.
So Australians should not
go too far in avoiding the
sun and should not ignore
dietary sources of vitamin D.
The only basic food routinely fortified with vitamin
D in Australia is margarine.
In the background is the
known toxicity of higher
doses of vitamin D, which
causes hypercalcaemia and
its consequences.
International units still
appear on bottle labels; 40
IU = 1µg vitamin D (cholecalciferol [D3] or ergocalciferol [D2]).
Vitamin E
1,25-hydroxyvitamin D3
(Active form)
Alpha tocopherol is the most
active of eight similar compounds with vitamin E activity, and the natural
stereoisomer “RRR” is more
active than the racemic
form, which is synthesised
chemically.
Fat-soluble vitamin E is
present in all cell membranes
where, being an antioxidant,
it is thought to reduce peroxidation of unsaturated
fatty acids by free oxygen
radicals.
Severe deficiency of vita-
submariners, do not need
the oral form of the vitamin.
Measurement of plasma
25OH vitamin D in population samples is now showing that in southern Australia not only housebound
old people but even some
young adults have low levels
at the end of winter.
min E is rare; it only occurs
in people with chronic fat
malabsorption, especially in
cystic fibrosis and abetalipoproteinaemia. There can
be ataxia, loss of tendon
jerks and pigmentary
retinopathy, which respond
to long-term vitamin E treatment.
Many people take vitamin
E supplements on their own
initiative, sometimes in large
doses well above nutritional
requirements. Earlier it was
rumoured to enhance virility (infertility had been the
first reported effect of deficiency in rats), but a doubleblind trial did not confirm
this.
In recent years the focus
has been on whether vitamin E’s antioxidant activity
Food sources of
vitamin D
n
Fish liver oils
Fatty fish (sardines,
herring, mackerel, tuna,
salmon, pilchards)
n Margarine (fortified)
n Infant milk formulas
(fortified)
n Eggs
n Liver
n
in vitro can reach sufficient
concentrations inside the
body to reduce atherogenesis. Two large-cohort epidemiological studies in the
US found less coronary
heart disease in people
taking vitamin E supplements. However, subsequently three randomised
intervention trials in Finland, Italy and Canada
failed to show any benefit.
The official nutritional
requirement is 10mg/day.
Although it is a fat-soluble
vitamin, tocopherol has low
toxicity. Few adverse effects
have been reported from
doses up to 3200mg/day.
Vitamin K
The “Koagulations” vitamin (first described in a
German journal) comes in
two chemical forms. Vitamin
K1 is found mostly in vegetables. The K2 vitamins are
produced by bacteria, for
example, in the gut.
Deficiency of vitamin K
manifests itself as a bleeding
disorder. The vitamin is necessary for synthesis of an
unusual amino acid (gammacarboxyglutamic acid) which
is part of the coagulation
factors II, VII, IX and X.
Vitamin K plays a role in
obstetrics, biliary surgery
and cardiology.
At birth vitamin K 1 is
given to prevent haemorrhagic disease of the newborn because transport
across the placenta is limited.
In adults vitamin K deficiency is to be expected in
obstructive jaundice and
other fat malabsorption syndromes, so that the vitamin
should be given before biliary surgery.
For people at risk of
thrombosis, oral anticoagulants of the warfarin
group owe their therapeutic
action to antagonism of vitamin K. Vitamin K1 is the
antidote and the effective
dose of anticoagulant can be
affected if a patient changes
consumption of green leafy
vegetables.
Vitamin K is also involved
in biosynthesis of a protein
involved in bone formation,
osteocalcin. Research is
under way to see if vitamin
K affects bone density or
turnover. There are not yet
any conclusive results.
Inorganic nutrients (minerals)
EIGHTEEN inorganic elements play roles in the function of
the human body and can be regarded as essential nutrients.
The possibility of one or two more is still being researched
and discussed.
Nine of these inorganic elements have some place in general
practice and are available in pharmaceutical products. For
each of these there is an official recommended nutrient intake
(dietary reference intake), ranging from 50µg/day for selenium to more than 2000mg/day for potassium (again, as for
vitamins, a 40,000-fold range of nutritional requirements).
Iron and calcium are used to fortify different foods —
fluoride is added to some cities’ drinking water and to toothpastes; iodide is added to some table salt (look for the label).
If fluoride intakes
are too high in
the first eight
years of life
teeth may
show mottling.
Where water is fluoridated
or naturally high in fluoride,
young children should use
junior toothpaste with halfstrength fluoride. If drinking
water is naturally low in fluoride and not fluoridated, fluoride tablets or drops should
be considered for young children for prophylaxis of dental
caries (0.25-1mg fluoride a
day, depending on water fluoride and age).
Fluoride
Sodium
The dentist’s nutrient. Communities overseas with 1ppm
naturally occurring fluoride have low rates of dental caries.
Australian cities have low water fluoride and the content is
brought up to that of communities with natural fluoride at
this safe level. Except for the possibility of fluorotic mottling of teeth (see below), there are no possible toxic effects of
fluoride as used in our water fluoridation.
An intake of 1-3mg/day — as occurs if drinking water has
fluoride added up to a concentration of 1mg/L — increases
the dental enamel’s resistance to acid produced by oral bacteria, especially if this fluoride is taken while enamel is being
laid down before teeth erupt in children.
Most toothpastes contain fluoride and if fluoride intakes
are too high in the first eight years of life teeth may show
mottling (not associated with any dysfunction).
Essentially common salt —
sodium chloride. The usual
medical advice to people is
to reduce intake because
average sodium intakes
are 150mmol/day or more
and the requirement is
40mmol/day or less. Intakes
less than 100mmol/day (2.3g
Na or 6g NaCl) contribute to
lowering blood pressure and
the NHMRC has been recommending this since 1982.
Most people eat more
sodium than they need and
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normal kidneys promptly
adjust urinary excretion to
the sodium intake.
Most salt in the diet is
added during food processing. Wheat flour, for example, contains 4mg Na per
100g but breads contain
500mg/100g or more.
There are nevertheless some
illnesses in which patients need
extra NaCl, for example,
Addison’s disease and some
cases of chronic renal failure.
There are preparations like
Slow Sodium for those who
find the taste of salt too strong.
The most common situation calling for extra sodium
is gastroenteritis in young
children. The need here is for
potassium, bicarbonate and
glucose with the NaCl. The
UNICEF oral rehydration
formula is NaCl 3.5g,
Na2CO3 5g, KCl 1.5g and
glucose 20g in a litre of
water. There are pharmaceutical products with similar
composition( eg, Gastrolyte).
Magnesium
Magnesium is the second
most abundant cation inside
cells, the fourth most abundant metal in the body, and
cofactor for several important enzymes.
Depletion (hypomagnesaemia) is almost always
secondary to disease — malabsorption, prolonged diarrhoea, vomiting and nasogastric suction, some renal diseases, loop diuretics and alcoholism.
Injections of magnesium
sulphate are used in the treatment of acute MI and in
obstetrics. Oral supplements
of several magnesium salts
are used for treating mild
cases of magnesium depletion
(some of which are listed
above) and also for indications with less strong evidence, for example, muscle
cramps and hypertension.
The RDI of magnesium is
300mg/day or 12mmol. Supcont’d next page
21 March 2003 | Australian Doctor |
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