The essential role of calcium (Ca2+) for our bones and teeth is unlikely to be news to anyone, with the discovery of calcium’s role in the development of rickets in infants and children in the 17th century.
This is an example of severe dietary calcium deficiency manifesting in soft bones, bone pain, muscle spasms and possible deformities, which occurs due to a lack of mineralisation in any of the skeletal structure. It later emerged that not only calcium, but other nutrients were essential in the prevention of this condition [rickets].
Synergistic nutrients required for proper calcium utilisation and metabolism for bone health include Vitamin D, phosphorus and protein. Studies have shown that deficiency in any of these nutrients significantly increases the risk of fractures. This reiterates the point we often make, in that assessment of single nutrients in isolation, whilst useful, does not provide the whole picture and context is essential. It can be seen from all of our nutrient spotlight features, that all nutrients require other nutrients either to support the conversion process to an active form, or assist with absorption, metabolism, transport and optimum utilisation.
Calcium is the most abundant mineral in the body, with the vast majority (99%) found in the bones and teeth.
The remaining 1% is found in the blood, nerve cells as well as other body tissues and fluids. This relatively small amount in the blood is critical however, with levels being maintained via highly sensitive negative feedback systems. That means that when requisite serum levels drop, this is corrected almost instantly, drawing calcium from our significant stores within the bones/teeth. This involves the endocrine system, particularly the parathyroid glands.
Vital roles of serum calcium include nerve transmission, muscle contraction and relaxation, healthy blood clotting and maintaining heart rhythm. Magnesium also has an essential role in maintaining this balance.
Calcium is also required for the absorption of Vitamin B12.
This essential mineral is absorbed primarily in the alkaline environment of the jejunum, in the small intestine. The presence of oxalates and phytates in foods, for example in spinach, can inhibit absorption.
Possible deficiency symptoms
- Muscle cramps and spasms
- Brittle nails
- Tingling, numbness in hands
- Rickets / Osteomalacia
- Increased risk of fracture (particularly in the elderly)
- Reduced bone density, leading to osteoporosis.
Note: other symptoms which may reflect disorders of calcium metabolism, resulting in too much or too little calcium in the blood, are extremely wide ranging, multi factorial and complex, requiring investigation by a medical practitioner.
Because of the abundant source of calcium stores in the bones as well as these systems, low serum calcium is unlikely to occur through dietary deficiency and if it does, requires investigation.
Some factors increasing demand / increasing risk of deficiency
- Adolescents, particularly female adolescents
- During pregnancy and lactation (absorption of calcium also increases during pregnancy)
- Older adults, particular post menopausal women
- Restrictive diets
- Eating disorders
Food sources include:
- Dairy products, milk, cheese, yogurt (consistently reported to have highest bioavailability of calcium)
- Tinned fish, such as sardines and salmon, containing soft, edible bones
- Soy and tofu
- Nuts and seeds (sesame seeds, and sesame seed products such as tahini, are a particularly good source)
- Dark greens, such as kale, broccoli and bok choy (spinach has reasonable calcium content, however only a small proportion is absorbed due to oxalates)
Bioavailability (that is, the extent to which a nutrient can be utilised and absorbed) is key when it comes to calcium. As described above, synergistic nutrients are required and the presence of oxalates and phytates can significantly impair absorption. Therefore, simply looking at calcium content without considering bioavailability is not representative.
It is our view that, in most cases, ensuring sufficient quantities of food sources of calcium is the best way of encouraging balance, as part of a varied diet to ensure the presence of the necessary synergistic nutrients. Supplementation should preferably be in consultation with a qualified nutritionist / medical practitioner, with individual context taken into consideration. A literature review determined that dietary sources of calcium in adequate quantities were as well absorbed and beneficial for bone health as supplements.