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Calcium
DESCRIPTION
Calcium is the most abundant
mineral in the human body, comprising over 1.5% of the total
body weight. About 99% of the body’s calcium is found
in the bones, with the remaining 1% in the soft tissues. Calcium
absorption is vitally dependent upon Vitamin D and consequently
Vitamin D and calcium deficiency symptoms are often synonymous.
When blood calcium levels
are low, Vitamin D hormone increases the level of calcium
in the blood by promoting the absorption of calcium and Phosphorus
from the intestine and from the bone. To maintain the body’s
physiological ratio of calcium to phosphorus, Vitamin D hormone
also increases the excretion of phosphorus - not calcium -
from the kidneys.
FUNCTIONS
Calcium is involved in the
structural formation of bones and teeth. It is also needed
for muscle and nerve function and blood clotting and the maintenance
of blood pressure. Small amounts are required in assisting
intrinsic factor in absorption of B12.
DEFICIENCY
Severe deficiency of calcium
in children may cause rickets, though the disease is more
commonly due to Vitamin D deficiency. The equivalent disease
in adults is osteomalacia.
An insufficiency of calcium
during a woman’s lifetime is thought to be related to
the development of post-menopausal Osteoporosis (brittle bone
disease).
More immediate pointers
of calcium deficiency are muscle spasms, Insomnia and irritability.
Allergies may also be aggravated by calcium deficiency.
The National Osteoporosis
Society recommend:
Men, pre-menopausal women
and menopausal women on HRT - 1000mg a day
Pregnant and lactating women
- 1200mg a day
Post-menopausal women (not on HRT) - 1500mg a day
CALCIUM BALANCE
The body maintains an ideal
blood calcium level at all times. If dietary calcium raises
this level, then the bone uptake of calcium increases. If
dietary calcium is low, then the bones release calcium (and
phosphorus) to maintain blood levels of calcium. Thus, low
dietary intake of calcium over a long period may lead to thinning
of the bones (osteoporosis).
REQUIREMENTS
Upper safe level for daily
supplementation = 1500mg
Recommended Daily Allowance: = 800mg
SUPPLEMENTAL USES
Calcium may be taken by
anyone who is worried that they may be at risk of calcium
deficiency. This could include:
Vegetarians and especially
vegans (1).
Women with a history of osteoporosis in the family (2).
Post-menopausal women (2).
Pregnant and lactating women (3).
High salt users, or users of aluminium-containing antacids
(these deplete calcium) (4).
SAFETY
Body calcium metabolism
is under such close regulation that an excessive accumulation
in blood or tissues through high intake is virtually unknown.
Where such accumulation does occur, it is due to a failure
of the control mechanisms.
Whilst there is a lot of
talk about calcium supplementation causing Kidney stones,
this is not backed up by scientific reports. In fact to date,
kidney stones have only been known to develop in cases where
there is disturbed calcium metabolism. People with properly
functioning control mechanisms seem perfectly safe in taking
calcium supplements even at high level.
INTERACTIONS AND CONTRA-INDICATIONS
Vitamin D
Calcium needs to be taken with Vitamin D , as this nutrient
is vitally important for calcium absorption.
Thiazide Diuretics
Doctors' advice should be followed before taking calcium with
diuretics drugs, as some (especially thiazides) increase the
calcium level of the blood.
Antibiotics
Patients who are prescribed tetracycline antibiotics should
take these a few hours apart from their calcium supplement.
Calcium should be avoided
by those with:
Conditions associated with
hypercalcaemia and hypercalciuria.
Chronic renal impairment.
Kidney stones or a history of kidney stones.
Those with high blood pressure should ensure their blood pressure
is monitored when supplementing with calcium (4).
FOOD SOURCES
Food (mg/100g)
Skimmed milk powder 1230
Cheese, cheddar 800
Sardines 550
Tofu 506
Dried figs 280
Evaporated milk 260
Watercress 220
Natural yoghurt 200
Milk, whole 103
Peanuts, roasted 61
Cabbage 57
Bread, wholemeal 54
Eggs 52
Fish, white 22
The main sources of calcium
in the diet are milk, cheese and other dairy products.
REFERENCES
1. Donovan UM and
Gibson RS. Dietary intakes of adolescent females consuming
vegetarian, semi-vegetarian, and omnivorous diets. J Adolesc
Health, 18;4:292-300, 1996.
2. Nordin BE. Calcium and Osteoporosis. Nutrition, 13;7-8:664-686,
1997.
3. "Dietary Reference Values for Food, Energy and Nutrients
for the United Kingdom", Dept. of Health, HMSO, 1991.
4. "Handbook of Dietary Supplements", Pamela Mason,
Blackwell Science, 1995.
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