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.
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.
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/a>
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).
Upper safe level for daily
supplementation = 1500mg
Recommended Daily Allowance: = 800mg
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).
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 (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.
Related News Stories
Smoking cigarettes can lower vitamin
D and calcium metabolism
A small study suggests oligofructose
helps the absorption of minerals.
A study involving calcium
supplementation could aid research into osteoporosis.
A study on the RDA of protein
suggests it could be higher for optimum absorption of calcium.
The links between calcium intake and
high blood pressure.
American research supports the
benefits of 1500mg calcium intake a day.
The importance of ensuring adequate
mineral intake in a vegetarian diet, which can sometimes be low
in minerals.
Vitamin K helps prevent against
diseases of the bone, like osteoporosis, and an adequate intake
should be ensured particularly for the elderly and vegetarians.
Multivitamins and vitamin E intakes
may help decrease the risk of colon cancer, studies suggest.
The effects of calcium supplements
on bone mineral density
The results of trials on
postmenopausal women suggest they may benefit from increased
intake of certain nutrients to protect against bone loss
It is common for smokers to have a
lower bone mineral density than non-smokers and various
suggestions have been put forward to explain this. However the
association is still not well understood.
Researchers in a recent study
provided strong evidence on why older adults should consume at
least 1300mg calcium daily.
The results of a study to see if
diet can modify calcium metabolism.
The buffering effect of essential
minerals is illustrated.
