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CALCIUM.TXT
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1995-03-13
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VegSocUK Information Sheet
THE VEGETARIAN SOCIETY
___________________________________
CALCIUM
Calcium is the most abundant mineral in the human body. Of the body's total
calcium, about 99% is in the bones and teeth where it plays a structural
role. The remaining 1% is present in body tissues and fluids where it is
essential for cell metabolism, muscle contraction and nerve impulse
transmission.
FUNCTIONS
The main function of calcium is structural. The skeleton of a young adult
male contains about 1.2 kg of calcium. There is continuous movement of
calcium between the skeleton and blood and other parts of the body. This is
finely controlled by hormones. Metabolites of Vitamin D are important in
this, increasing reabsorption of calcium by bones.
Calcium also plays a role in cell biology. Calcium can bind to a wide range
of proteins altering their biological activity. This is important in nerve
impulse transmission and muscle contraction. Calcium is also needed for blood
clotting, activating clotting factors.
Vitamin D is needed for absorption of dietary calcium and so calcium
deficiency may be linked with rickets in children. In adults, calcium
deficiency may lead to osteomalacia (softening of bones). This may be related
to repeated pregnancy with lengthy breast feeding.
Osteoporosis can be due to calcium deficiency. This involves loss of calcium
from the bones and reduced bone density. This causes bones to be brittle and
liable to fracture. Bone loss occurs with age in all individuals. This
usually occurs after 35-40 years and involves the shrinking of the skeleton.
Bone loss is greatest in women following the menopause. This is due to
reduced levels of the hormone, oestrogen. Postmenopausal women are
particularly at risk from osteoporosis.
Some research has indicated vegetarian women are at less risk of osteoporosis
than omnivorous women. This is thought to be due to animal protein increasing
calcium loss from bones. However, other research has found no difference
between vegetarians and omnivores.
The risk of osteoporosis may be altered by factors other than diet. Lack of
exercise, being underweight, smoking and alcohol can all increase the risk.
A low level of calcium in the blood and tissues can cause hypocalcaemia. This
involves sensations of tingling and numbness and muscle twitches. In severe
cases muscle spasms may occur. This is called tetany. It is more likely to be
due to a hormonal imbalance in the regulation of calcium rather than a
dietary deficiency.
Excess calcium in the blood can cause nausea, vomiting and calcium deposition
in the heart and kidneys. This usually results from excessive doses of
vitamin D and can be fatal in infants.
DIETARY SOURCES
Calcium is present in a wide range of foods. Dairy products, leafy green
vegetables, nuts and seeds (almonds, brazils, sesame seeds), tofu, and dried
fruit are all good sources of calcium for vegetarians. Most flour is
fortified with calcium carbonate so cereals can also be a good source. Hard
water may also provide calcium. Meat is a very poor source of calcium.
Calcium balance can be affected by a range of other factors. Vitamin D is
essential for absorption of calcium from the gut. This is because calcium is
transported into the body by a special carrier protein which requires vitamin
D for its synthesis.
A number of substances can inhibit the absorption of calcium. Phytic acid,
found in bran, whole cereals and raw vegetables is one of these. Uronic acid,
a component of dietary fibre, and oxalic acid, found in certain fruits and
vegetables can also bind calcium. However, diets habitually high in these
acids are not thought to have a major effect on calcium absorption. Saturated
fats can also lessen calcium absorption.
Calcium is lost in the faeces, urine and sweat. Calcium loss is roughly equal
to dietary calcium in adults. Calcium loss is reduced if dietary calcium is
low. Adaptation to both high and low calcium intakes occur. Reduced intake
leads to increased efficiency of absorption. In infants and children calcium
is retained for new bone growth. Calcium is also lost during lactation in
breast milk.
Good sources of calcium (single servings).
Broccoli, boiled (95g or 3 1/2 oz) 72 mg
Spinach, boiled (130g or 5 oz) 208 mg
Chick peas, boiled (200g or 8 oz) 92 mg
Baked beans (200g or 8 oz) 90 mg
Tofu (60g or 2 oz) 304 mg
Dried figs (4 figs) 168 mg
Sesame seeds (15g or 1/2 oz) 20 mg
Brazil nuts (9 nuts, 30 g) 54 mg
Cows milk (1/3 pint) 234 mg
Cheddar cheese (slice, 40 g) 288 mg
Soya cheese (slice, 40 g) 180 mg
Fair sources
Brown bread (2 slices) 70 mg
Dried apricots (8 apricots) 46 mg
Cottage cheese (45g or 1 1/2 oz) 33 mg
French beans, boiled (100g) 41 mg
Poor sources
Spaghetti, boiled (100g or 3 1/2 oz) 7 mg
Brown rice (190g or 8 oz) 7 mg
REQUIRED INTAKES
The old Recommended Daily Amounts (RDAs) have now been replaced by the term
Reference Nutrient Intake (RNI). The RNI is the amount of nutrient which is
enough for at least 97% of the population.
Reference nutrient intakes for calcium, mg/day.
Age RNI
0 to 12 months 525 mg
1 to 3 years 350 mg
4 to 6 years 450 mg
7 to 10 years 550 mg
11 to 18 years, male 1000 mg
11 to 18 years, female 800 mg
19 + years 700 mg
Breast feeding women 1250 mg
During pregnancy, calcium absorption from the gut increases and no additional
calcium is generally needed. Pregnant adolescents are an exception to this,
having particularly high calcium needs.
Breast feeding women need an extra 550 mg of calcium. A lactating women can
lose up to 300 mg a calcium/day in breast milk.
Calcium absorption decreases with age so it is important the elderly have
adequate dietary calcium.
MEAL PLAN
Sample one day's meal plan to meet the RNI of 700 mg for an adult
Breakfast
Muesli 114 mg
Soya milk, unfortified 15 mg
Lunch
2 slices of brown bread toast 140 mg
Baked beans (200g or 8 oz) 90 mg
Evening meal
Tofu (60g) with broccoli (95g) 376 mg
Brown rice, boiled (165g) 7 mg
Total calcium intake 742 mg
___________________________________
//
This article is copyright to the Vegetarian Society (UK), but may be freely
copied for non-commercial use provided it is kept intact, not altered
and these lines are included.
For futher information contact: The Vegetarian Society, Parkdale, Dunham Road,
Altrincham, Cheshire WA14 4QG, England. Tel: (England) 061 928 0793
email: vegsoc@vegsoc.demon.co.uk
//
[The text of this file was obtained from the Vegetarian Society (UK) in
March 1995.]