Calcium is one of the most plentiful minerals in our body. Most of it – about 99 per cent – is stored in our bones and teeth, where it is essential for their structure. Calcium is not just important for bones and teeth, however – it also has vital roles in muscle and nerve function, for energy, for normal blood clotting, and even for our digestion. Because it’s the most plentiful mineral, we need quite a lot of it compared to most other minerals – between around 800 to 1000 mg a day.
Primary functions of Calcium
- Calcium is vital for strength of our bones and teeth, where it is stored together with phosphorus as part of a substance called hydroxyapatite. The bones also act as a store of calcium for its other vital roles, and so if our calcium intake is not adequate, it will be taken from the bones, potentially leading to a reduction in bone strength. Calcium together with vitamin D is needed for bone growth in children, and can help prevent bone mineral loss in women after menopause.
- Calcium is essential for the transmission of nerve impulses around the body. Without calcium, we wouldn’t be able to think, feel or move!
- Calcium is needed for muscle contraction. Muscle fibres contract when calcium ions flood into muscle cells, causing more calcium to be released from storage inside the cell, which causes the fibres to contract. As part of this role, it is also needed for our blood vessel walls to contract and relax, allowing blood to flow normally around the body.
- Calcium is needed for normal blood clotting – it activates several ‘blood clotting factors’ that also depend on vitamin K. Our blood needs to clot to stop too much being lost when we’re injured.
- Calcium helps the enzymes in our body to work. This includes the digestive enzymes in our gut that break down our food so we can absorb it.
- Calcium is needed in the process of cell division. This means it’s necessary for all processes of growth and repair in the body.
How much calcium do we need?
The nutrient reference value for calcium in the UK is 800 mg for adults. Nutrient reference values refer to the amount needed to ensure that the needs of nearly all the population (97.5%) are being met. The tolerable upper level for daily intake for adults is set at 2500 mg; however, it is not generally advised to take more than 1000mg in supplement form.
Deficiency signs and symptoms*
Calcium levels have to be very tightly regulated in the blood to keep us alive. This means that – as mentioned above – if we aren’t consuming enough calcium, the bones will give up their stores to maintain the right level in the blood. As a result, the main consequences of calcium deficiency will be weakened bones and potentially osteoporosis.
The primary symptom of weakening bones or osteoporosis is fractures.
If blood calcium levels do fall low – which may be due to another condition such as lack of parathyroid hormone production, poor kidney function or vitamin D deficiency – then symptoms can be many and varied, including anxiety, palpitations, numbness and cramping, insomnia, pain and cognitive impairment (memory, reasoning, learning, etc.).
*If you experience any of these symptoms, please consult your doctor or health practitioner.
The best food sources of calcium include:
- Dairy foods – milk, cheese, yoghurt and some whey proteins. One of the best sources of calcium is parmesan cheese, which contains almost 1,400mg of calcium per 100g! Milk and yoghurt contain around 120mg per 100g, and other cheeses anywhere in between.
- Bone broth. Making your own bone broth by simmering left-over bones (e.g. a chicken carcass) for several hours is an excellent way to get easily absorbed calcium and other bone minerals.
- Green leafy vegetables: per 100g, kale contains around 200mg of calcium, watercress 120mg and spinach
- Canned sardines or salmon, when eaten with the soft bones. A can of sardines can contain up to 350mg of calcium!
- Nuts – especially almonds. Almonds contain around 250mg of calcium per 100g. However, an average serving is more likely to be around 20 grams, giving you around 50mg of calcium.
- Seeds – especially sesame seeds and chia seeds. Sesame seeds contain almost 1000mg and chia seeds around 630mg of calcium per 100g, but this is equivalent to just 90mg and 60mg in a tablespoon. Tahini, made from sesame seeds, contains around 420mg of calcium per 100g, equivalent to around 60mg per tablespoon.
Forms and bioavailability / What to look for when buying a supplement
When looking at calcium supplements, it’s important to note that some forms of calcium are more absorbable than others.
- Calcium carbonate can be a common form used in cheaper supplements. It is generally thought to be poorly absorbed compared to some other forms such as calcium citrate, especially for people who have low stomach acid.
- Calcium citrate is perhaps the next most common form found in supplements. It is thought to be a good form for absorption when compared to carbonate (as above).
- Calcium gluconate and calcium bisglycinate (which may be seen as ‘chelated calcium’) are also considered good forms of calcium for absorption.
- ‘Whole food’ calcium contains natural calcium, often from seaweed or marine algae. Whereas most supplements contain an ‘isolated’ calcium, ‘wholefood’ forms contain naturally occurring calcium from the seaweed/algae, together with small amounts of other minerals. Again, this form is considered well absorbed, and may actually be better utilised in the body compared to a standard calcium supplement.
- Calcium hydroxyapatite provides whole hydroxyapatite – the form in which calcium is naturally found in bone. There seems to be little information on how absorbable this form is compared to other forms of calcium.
As general advice, we would recommend choosing citrate, gluconate, bisglycinate (chelated calcium) or whole food calcium from seaweed or algae as the best forms.
Which other minerals and vitamins work with calcium?
It’s important to note that calcium does not work in isolation and doesn’t build healthy bones on its own. Here are some of the other important nutrients we need for our bones.
- Magnesium. Magnesium is another mineral that is stored in and necessary for the health of our bones and teeth. Magnesium deficiency may lead to low calcium levels in the blood. Magnesium also works with calcium in nerve transmission and normal muscle function.
- Vitamin D. Vitamin D is required for our body to absorb enough calcium, and may also promote bone mineralization (the binding of minerals such as calcium into the bone).
- Vitamin K. This vitamin helps to bind minerals such as calcium into the bones, by activating bone proteins. It has been found that vitamin K2 (mainly found in fermented foods) has greater effect on bone strength than K1 (found in green leafy vegetables).
- Others nutrients include: vitamin C, vitamin A, zinc, manganese and boron.
The main point here is that a generally nutrient-rich diet is a better way to support our bones rather than focusing on calcium-rich foods; and if you’re looking for a bone support supplement, it’s best to make sure you’re getting good levels of the three main nutrients described above together with your calcium. (See the separate articles on all of these three nutrients for more information.)
Dosages: Lifestyle Labs’ recommendations
Adults: Calcium supplements for adults typically provide between 300 mg and 1,000 mg in a full daily dose. This may depend on the form of the calcium: calcium carbonate supplements tend to be towards the higher end of this range, and you may need more of it make sure you’re absorbing enough. But calcium as bisglycinate, gluconate, citrate, or ‘whole food’ calcium may provide just 400mg per daily dose – and because it’s better absorbed, most people don’t need to take any more than this. Each person’s ‘ideal’ amount can also be very dependent on how much they are getting in their food, and their individual health circumstances.
If you are taking a supplement that recommends a higher dose (e.g. 1000mg) then it is best to take no more than 500mg at one time, to support better absorption and reduce its impact on absorption of other minerals from food or supplements (see ‘Safety’ below).
Children: A children’s calcium supplement may contain around 200 to 300 mg of calcium, and more than this is not normally recommended unless on the advice of a healthcare practitioner.
If you are taking any medications or have any medical condition, please consult your healthcare practitioner before taking calcium.
It’s important to note that taking calcium at the same time as other minerals can interfere with their absorption. This applies especially to magnesium, zinc and iron. If you are taking any of these other minerals separately or as part of a multivitamin, it is advisable to take them at a different time of day to the calcium.
- Heller HJ et al. Pharmacokinetics of calcium absorption from two commercial calcium supplements. J Clin Pharmacol. 1999 Nov;39(11):1151-4.
- http://lpi.oregonstate.edu/mic/minerals/calcium. This link leads to a website provided by the Linus Pauling Institute at Oregon State University. Lifestyle Labs is not affiliated or endorsed by the Linus Pauling Institute or Oregon State University.
- Aranow C. Vitamin D and the immune system. J Investig Med.2011 Aug;59(6):881-6.
- Knapen M H J et al. Vitamin K2 supplementation improves hip bone geometry and bone strength indices in postmenopausal women. Osteoporos Int. 2007 Jul; 18(7): 963–972.