Calcium is the most abundant mineral in the human body. On average, calcium makes up about 2.3% of a person’s body weight. Nearly all calcium in the body is stored in the bones and teeth. The body needs a ready supply of calcium to keep bones strong. Even after we have stopped growing bone is constantly being remodelled meaning bone is broken down and rebuilt with mineral deposits to replace the bone material that has been lost. Calcium is also needed for other body processes so if blood or tissue calcium levels become low calcium is released from the bones.
Dietary requirements for calcium are largely determined by the amount needed for bone development and maintenance. This need varies throughout life, with greater requirements during childhood and adolescence, pregnancy, lactation and later life. There is considerable disagreement among experts as to what the recommended daily calcium intake should be for different groups (1). That said, it is fairly well established that many people do not reach the recommended daily intake of calcium. In those at risk of fractures, calcium supplements are generally recommended.
Calcium in Childhood and Later Life
During childhood there is a great need for the minerals involved in bone health. Most individuals can continue to build bone mass until their mid-30s. However, after age 35, they can only slow the rate of bone loss, which is a natural part of ageing. Bone loss accelerates after the menopause in women, as well as in men as they age.
Inadequate dietary calcium in early life impairs bone development. Calcium supplementation for periods of up to 3 years has been shown to enhance bone mineral status in children and adolescents. However, it is unclear whether this benefit is long term.
In later years inadequate dietary calcium accelerates bone loss and may contribute to osteoporosis. Calcium supplementation in post-menopausal women and older men has been shown to reduce the loss of bone mineral density over periods of 1–2 years. However, the extent to which this outcome reduces fracture risk needs to be determined. Even allowing for disagreements on recommended intakes, evidence indicates that dietary calcium intake is inadequate for maintenance of bone health in a substantial proportion of people, particularly adolescent girls and older women (1).
Calcium, Vitamin D and Bone Health
Vitamin D improves the absorption and utilisation of calcium. Vitamin D supplementation is especially important in elderly people because skin synthesis and absorption of vitamin D is often impaired.
A high dietary calcium intake combined with vitamin D can increase bone density and reduce fractures in older women and probably men. The Institute of Medicine in the US recommends that people aged 19 to 50 years of age consume 1,000mg of calcium per day and that people over the age of 50 consume 1,200mg per day. The average American consumes less than 800mg of calcium per day (2).
Other Functions of Calcium
Calcium is also vital for:
- Teeth development and prevention of decay
- Blood clotting
- Muscle contraction
- Regulating the heartbeat
- Enzyme and hormone secretion
- Functioning of the central nervous system.
- Conduction of nerve impulses that send messages through the central nervous system
- Blood vessel and muscle contraction and expansion
- Regulation of fluid balance by controlling the flow of water into and out of the cells
- Enzyme and hormone secretion
When calcium levels in the blood fall too low, the bones release calcium to tissues and fluids so that normal body functions can continue. Ultimately this can lead to thinning of the bones and an increased risk of fractures.
Reasons for Calcium Citrate
Supplements containing calcium citrate and calcium carbonate complexes are the most frequently used. A recent meta-analysis found that absorption of calcium citrate was 27% higher than that of calcium carbonate when taken on an empty stomach and 22% higher when taken with meals (2,3). In another study, 500mg of calcium citrate taken with breakfast produced serum calcium levels significantly higher than those after the same amount of calcium carbonate (2,3).
Calcium citrate is suggested as being a valuable product for the management of several chronic conditions, in particular, those with, or at risk of, osteoporosis as well people with low stomach acid and chronic hypo-parathyroidism. Excess calcium can be implicated in kidney stones although citrate salts have an inhibitory effect on kidney stone formation (4).
Other Ways to Improve Calcium Absorption
Taking calcium with food in dosages of 500mg or less increases absorption. Foods such as spinach, rhubarb and wheat bran can decrease calcium absorption so it’s best to take calcium supplements away from these foods.
Calcium can interfere with absorption of iron, zinc and some medications including bisphosphonates and some antibiotics so should not be taken at the same time as these supplements and medications. Check with your medical specialist before supplementing with calcium, especially if you take any medications or have a medical condition.
Side Effects of Calcium Supplementation
The most common adverse effects of calcium supplements are constipation, intestinal bloating and excess gas. Adverse effects occur most frequently with calcium carbonate. Switching to calcium citrate and increasing fluid intake may relieve symptoms. Patients who form calcium-containing stones are generally advised not to take calcium supplements. However, a low intake of calcium can aggravate the risk of stone formation by increasing absorption and urinary excretion of oxalate so a balance must be struck.
Tom Oliver’s Calcium Citrate
Those who could benefit from calcium supplementation include:
- Adolescent girls
- Menopausal and post-menopausal women
- Older men
- Those on restricted diets
- Those with dairy intolerance
- People with low stomach acid
- Anyone at risk of osteoporosis
- People with hypo-parathyroidism
- Pregnant or lactating women