What is calcium?
Calcium is the main component of bone. It makes up about 67 per cent of human bone tissue with the remaining 33 per cent being made up of collagen fibres. Collagen gives the bone flexibility while calcium gives it strength and rigidity. Ninety-nine per cent of calcium in the body is found in the bones and teeth. Calcium is deposited by specialised bone cells which are controlled by a hormone from the thyroid gland.
It is estimated that the whole skeleton is replaced every seven to 10 years in adults and every two years in children, so a regular intake of calcium is required. Other cells in the body such as the heart, nerves and muscles also require calcium to function normally. If blood levels of calcium become low, the body will take calcium from the bones - this may result in weakened bones if this calcium is not replaced.
Calcium deposits and bone density can be laid down in bones until the age of about 30. Whether or not you develop osteoporosis later in life can be dependent on the level of bone mass acquired during these early years.
When is it necessary to take extra calcium?
Calcium supplements are necessary in a number of situations. For example, people with hypothyroidism, a condition in which the thyroid gland does not work effectively, may require calcium supplements. Children who suffer from milk allergies or multiple food allergies may also require additional calcium. Some strict vegetarians may lack calcium as a result of dietary insufficiencies.
Calcium requirements are greatest during growth periods, including pregnancy and lactation. Lowered progesterone levels, such as following the menopause, can cause bone loss if dietary intake of calcium is low so post-menopausal women are also given calcium supplements.
Osteoporosis is a condition in which the bones lose calcium and become porous and brittle as a result. This leads to an increased incidence of fractures, particularly in post-menopausal women. Hip fractures can be fatal in around 10 to 15 per cent of cases and other fractures can cause permanent disability and deformity. It is very important to ensure that sufficient calcium is taken before osteoporosis or bone weakness occurs - prevention is a continual process and should be a lifelong consideration.
How much calcium should be taken additionally?
Medical advice should be obtained regarding the level of calcium it is necessary for you, as an individual, to take. Calcium is available as a number of different salts including carbonates, gluconates, lactates and phosphates. Calcium supplements are available in a number of different presentations including chewable tablets, effervescent tablets, powders and liquids. They are usually taken once a day.
Calcium and vitamin D supplements have been proven to reduce the risk of hip fracture in frail older people.
The only side effect of calcium supplements may be gastric irritation, therefore, people with ulcers or other gastric problems may need careful observation.
Recommended daily calcium intakes
Adults (men and women, including pregnant women*).......700mg
Boys 11-18 years...........................................................1000mg
Girls 11-18 years............................................................800mg
Children 1-3 years..........................................................350mg
Children 4-6 years..........................................................450mg
Children 7-10 years........................................................550mg
*women who are breastfeeding may require additional calcium
Examples of calcium content of foods
100ml milk (full cream, skimmed or semi-skimmed) = 118mg, 120mg and 122mg, respectively
100g fruit yoghurt = 122mg
100g cheddar cheese = 739mg
100g cottage cheese = 127mg
100g white bread = 177mg
100g wholemeal bread = 106mg
100g pilchards in tomato sauce = 250mg
100g sardines in tomato sauce = 430mg
Self-help measures to strengthen bones:
- Ensure youeat a balanced diet that includesenough calcium-containing foods (see recommendeddaily intakes above). Avoid eating excessive amounts of protein or salt as this can result in loss of calcium. Your salt intake should not exceed 6g per day.
- Take regular weight-bearing exercise (eg, jogging, walking, dancing).Exercise strengthens the bones and helps the body to store calcium.
- Increase calcium intake at particular times of life when calcium needs are greater, such as during pregnancy and breast feeding and after the menopause. Women should ensure that they increase their calcium intake at these times so that calcium is not taken from their bones causing bone weakness.
- Avoid smoking, excess caffeine and excess alcohol - these can all interfere with calcium levels, particularly if the dietary calcium intake is low.
- Maintain a healthy body weight - being overweight is bad for your health in generalwhile being underweight can increase the risk of broken bones if you fall.
Further information
British Nutrition Foundation
High Holborn House
52-54 High Holborn
London WC1V 6RQ
Tel: 020 7404 6504
Email: postbox@nutrition.org.uk
Internet: www.nutrition.org.uk
National Osteoporosis Society
Manor Farm
Skinners Hill
Camerton
Bath BA2 0PJ
Tel: 01761 471771
Helpline: 0845 4500 230 (Monday to Friday, 9am-5pm)
Email: nurses@nos.org.uk
Internet: www.nos.org.uk
Fact sheet provided by MIMS
Date last reviewed: March 2008
