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 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
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).
- Those following very low fat diets, as they are relient on sun exposure only as a source of Vitamin D
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
Calcium needs to be taken with Vitamin D, as this nutrient is vitally important for calcium absorption.
Doctors' advice should be followed before taking calcium with diuretics drugs, as some (especially thiazides) increase the calcium level of the blood.
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).
Skimmed milk powder 1230
Cheese, cheddar 800
Dried figs 280
Evaporated milk 260
Natural yoghurt 200
Milk, whole 103
Peanuts, roasted 61
Bread, wholemeal 54
Fish, white 22
The main sources of calcium in the diet are milk, cheese and other dairy products.
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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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