Dr Sarah Brewer explores the benefits of calcium, what happens if you're deficient, how to get calcium from your diet and what supplements are available.
Calcium has so many structural and metabolic roles in the body that we each harbour around 1.2kg of the mineral – more than any other – most of which is stored in our skeleton as hydroxyapatite.
Although 99 per cent of the dietary calcium you absorb goes straight into your bones and teeth, the other 1% is vital for blood clotting, muscle contraction, nerve conduction and the production of energy.
The best-known sources of calcium are cows' milk and dairy products, but it is also found in eggs and tinned salmon (if the tinned salmon includes the soft bones). For adults in Australia, about 60% of calcium intake comes from milk sources.
For those who follow a plant-based diet, or who have lactose intolerance, calcium can also be obtained from nuts and seeds, pulses, bread made from fortified flour and green leafy vegetables, especially broccoli (but not spinach, whose oxalate content reduces its uptake).
Some types of dietary fibre (phytates from wheat in unleavened breads such as chapati) also bind to calcium in the gut to reduce its absorption.
Did you know? A pint of skimmed or semi-skimmed milk contains around 720mg calcium – almost all your daily requirement.
The role of vitamin D
Calcium is only absorbed from your small intestine when sufficient vitamin D is present. Good intakes of both calcium and vitamin D are therefore vital throughout life to build strong bones and to help prevent bone thinning in later life.
Vitamin D regulates calcium metabolism and normal blood levels by:
- Increasing absorption in the small intestines
- Regulating calcium reabsorption in the kidneys
- Regulating secretion of parathyroid hormone, which releases calcium from bones
Calcium and Vitamin D
Chewable tablets for bone and teeth health
- Calcium and vitamin D to support teeth and bones
- Added vitamin K to help maintain bone health
- Helps reduce the loss of bone mineral linked to menopause
Benefits of calcium
You need sufficient calcium to build strong bones and to help prevent bone loss in later life.
A large analysis of clinical trials involving almost 31,000 adults suggested that calcium supplements (taken together with vitamin D) can reduce the rate of bone loss and reduce the risk of all types of fracture by 15% and of hip fracture by 30%.1
Calcium supplements are therefore a good idea for middle-aged and older adults, including postmenopausal women.
What else can calcium help?
Calcium also has a key role in ensuring healthy blood clotting, cell division and specialisation, muscle contraction, nerve transmission, the production of energy and for digestive enzymes to work properly.
Did you know? Vitamin K2 helps to ensure calcium is moved away from the arteries and laid down in the bones.
How much calcium do I need per day?
The EAR (estimated average requirement) for calcium for men between 19 and 70 years of age and women between 19 and 50 years of age is 840mg. For men over 70 years of age and women over 50, this rises to 1,100mg.
The RDI (recommended daily intake) for calcium is 1,000mg for men between 19 and 70 years of age and women between 19 and 50 years of age – and 1,300mg for men over 70 years of age and women over 50.
These are the definitions used by the Australian Government in the 'Nutrient References Values for Australia and New Zealand'.
EAR (estimated average requirement) – the daily nutrient level estimated to meet the requirements of half the healthy individuals in a particular life stage and gender group.
RDI (recommended daily intake) – the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98 per cent) of healthy individuals in a particular life stage and gender group.
If you avoid dairy foods due to intolerances or are cutting back to lose weight, you may not get your full calcium requirement.
If you are lacking in vitamin D, you will not absorb calcium well, either.
In Australia, 23 per cent of people are estimated to have vitamin D deficiency.2 In autumn and winter it becomes even more common, and is most prevalent in the south-eastern states of Victoria (49%), ACT (49%), and Tasmania (43%).3
When intakes of calcium (or vitamin D) are low, the body attempts to replenish blood levels by leaching calcium from your bones, leading to thinning (osteoporosis). Those at greatest risk of calcium deficiency include women (especially those who are pregnant, postmenopausal or who have an eating disorder), individuals with milk allergy or lactose intolerance, adolescents and the elderly.4
Some studies have suggested that the most effective doses for preventing bone loss in later life is 1200mg calcium plus 800IU (20mcg) of vitamin D.5
Low intakes of calcium are also linked with muscle aches and pains, twitching, spasm and cramps, heart palpitations, high blood pressure, osteoporosis, gum disease and loose teeth.
Supplements that contain calcium carbonate provide the most elemental calcium at 40mg per gram, and this is generally well tolerated and absorbed, especially when taken with food.6
Calcium citrate provides 21mg elemental calcium per gram, although this lower calcium content is partly compensated by greater absorption.
Calcium lactate contains 13mg per gram, and calcium gluconate 9mg per gram.7
Calcium tablets usually include other bone-friendly nutrients such as vitamin D3, vitamin K2, magnesium, boron, copper and zinc.
Select a supplement made to pharmaceutical standards (GMP) to ensure it provides a consistent dose that meets label claims.
How to take calcium tablets
Calcium tablets are best taken with meals. Some evidence suggests that they are better taken with an evening meal rather than breakfast, as the movement of calcium in and out of cells is greatest at night, when growth hormone is secreted.
If taking a high dose, however, it is usually best to divide it into two or three smaller doses spread throughout the day to maximise the amount you absorb.
Those taking certain medications, such as tetracycline antibiotics, need to ensure they do not eat or drink calcium-containing foods for at least an hour either side of taking their medication. This is because calcium binds with some tetracyclines to reduce their absorption.
Safety: can I take too much calcium?
Some studies have found a slightly increased risk of heart disease in people taking calcium supplements, but others have not. Studies finding a link have tended to take place in countries where vitamin D deficiency is common, such as Sweden, where up to one in two people are lacking in vitamin D during the winter months.8
According to the National Osteoporosis Foundation and the American Society for Preventive Cardiology, calcium supplements (with or without vitamin D) have no harmful effects on the risk for cardiovascular and cerebrovascular disease in generally healthy adults if calcium intake (from food plus supplements) does not exceed 2,000mg per day, and should be considered safe from a cardiovascular point of view.9,10
The Australian Government quote 2,500mg a day as the upper level of safe intake from food and supplements.11
People with a known tendency to form kidney stones should seek advice before taking calcium supplements (and drink sufficient fluids).12