Calcium: what are its benefits for the body, beyond bone health?

When calcium is mentioned, the image that comes to mind is that of a solid skeleton and a glass of milk. It is not wrong, but it is incomplete. The benefits of calcium go far beyond the skeletal sphere. This mineral is involved in every muscle contraction, every nerve impulse, and every stage of clotting.

But it must be absorbed. The ingested quantity does not tell the whole story: without vitamin D, vitamin K2, and magnesium, part of the calcium provided does not fulfill its role. Understanding the benefits of calcium therefore also means understanding its journey in the body, from the plate to the bone.

Calcium is the most abundant mineral in the human body. An adult contains about one kilogram of it. The body does not know how to make it: it must therefore find it every day in the diet.

Almost all calcium is stored in the bones and teeth. It is associated with phosphorus there in the form of hydroxyapatite crystals, deposited on a framework of collagen fibers. This mineral and protein architecture gives the skeleton both its rigidity and a certain flexibility.

Contrary to popular belief, bone is not static tissue. It is constantly renewed thanks to two types of cells. Osteoclasts resorb old bone, while osteoblasts build new bone. In adults, a significant part of the skeleton is thus remodeled every year.

This remodeling makes the skeleton a true calcium reserve, from which the body draws when intake is insufficient.

The remaining 1% circulates in the blood and cells. This circulating calcium is vital. Its blood level, blood calcium, is therefore maintained within a very narrow range, around 2.2 to 2.6 mmol/L.

Three hormones ensure this balance:

• the parathyroid hormone (PTH), secreted by the parathyroid glands;
• the calcitriol, active form of vitamin D;
• the calcitonin, produced by the thyroid.

When blood calcium levels tend to drop, PTH mobilizes bone calcium and vitamin D increases its intestinal absorption.

In other words, normal blood calcium levels do not mean that intake is sufficient. It may simply indicate that the skeleton is silently compensating. This is one of the keys to understanding the benefits of calcium: the body sacrifices the bone reserve to preserve vital functions.

The European Food Safety Authority (EFSA) evaluated the roles of calcium based on scientific literature. European Regulation No. 432/2012 retains eight of them, which precisely define the benefits of calcium that can be claimed.

Calcium contributes to the maintenance of normal bones and normal dentition. In children, it is necessary for normal bone growth and development.

The link between calcium and bone plays out throughout life, but it is not the same in nature depending on age:

• until 25-30 years, the body builds its bone capital and reaches what is called the peak bone mass;
• then, the challenge becomes preserving this capital, which gradually erodes with age.

A systematic review published in 2016 by Weaver and colleagues analyzed all lifestyle factors associated with peak bone mass. It confirms the role of calcium intake and physical activity during childhood and adolescence. The capital built early conditions the bone density of the following decades.

For teeth, calcium is part of the composition of enamel and dentin, which are also made of hydroxyapatite.

Calcium contributes to normal muscle function. When a muscle receives the order to contract, calcium is released from an intracellular structure, the sarcoplasmic reticulum. It then binds to a protein, troponin, which allows actin and myosin filaments to slide over each other.

Without calcium, no contraction. This mechanism concerns both skeletal muscles and heart muscle, which illustrates the extent of the benefits of calcium beyond the skeleton.

Calcium contributes to normal neurotransmission. At the end of a neuron, the arrival of the nerve impulse opens calcium channels. The entry of calcium then triggers the release of neurotransmitters in the synapse, the space that separates two nerve cells.

Each message transmitted between neurons thus depends on a precisely dosed flow of calcium.

Calcium contributes to normal blood clotting. Several stages of the clotting cascade, which results in the formation of the clot, depend directly on it.

Interestingly, some clotting factors can only bind calcium after being activated by vitamin K. Here we find, right from clotting, the calcium and vitamin K duo that also plays a central role in bone.

Calcium contributes to normal energy metabolism and the normal functioning of digestive enzymes. It acts as an intracellular messenger, capable of activating many enzymes involved in energy production and in the digestion of nutrients.

It also plays a role in the process of cell division and specialization. This role completes the picture of the benefits of calcium: a structural mineral, but also an omnipresent biological signal.

Calcium is often presented as the ally of strong nails and thick hair. The nutricosmetic approach however requires distinguishing what is established from what is popular belief. Regarding appendages, none of the benefits of calcium is recognized at the European level.

The nail is mainly composed of keratin, a fibrous protein. Its calcium content is low and does not determine its hardness. A review published in 2010 by Cashman and Sloan on the links between nutrition and nails recalls this: their resistance depends above all on their hydration, the quality of the keratin, and the status of several micronutrients.

The repeated cycles of wetting and drying are moreover one of the first causes of brittle nails. On the nutrition side, it is zinc and selenium that contribute to the maintenance of normal nails, according to the authorized claims. The same logic applies to hair, also made of keratin, whose quality of the hair fiber depends on other nutritional levers.

In the skin, calcium plays a real physiological role. The epidermis presents a calcium gradient:

• the concentration is low in the basal layer, where keratinocytes are born;
• it is high in the upper layers.

This gradient serves as a signal. Research by Elias and his team on experimental skin models has shown that it guides keratinocyte differentiation and the formation of the skin barrier.

However, this gradient is a local organization specific to the epidermis. No data shows that oral calcium intake alters it. Calcium is a player in skin biology, not a nutricosmetic active for the skin.

Calcium requirements vary by age and life stage. French references are set by ANSES, in line with EFSA.

On food supplement labels, the nutrient reference value (NRV) is set at 800 mg. It serves as a standard to express a percentage of intake, without exactly corresponding to the needs of each age.

Adolescence is the period when daily calcium intake matters most. A large part of the bone capital is built in a few years around puberty.

During pregnancy and breastfeeding, requirements remain those of an adult, because intestinal absorption naturally increases. It is still necessary that intakes are sufficient. In case of pregnancy or breastfeeding, it is important to seek advice from a healthcare professional before any supplementation.

At menopause, the drop in estrogen accelerates the loss of bone density during the first few years.

Finally, after 60 years, two mechanisms combine:

• intestinal absorption of calcium decreases;
• the skin synthesizes vitamin D less efficiently.

EFSA sets the upper safety limit at 2,500 mg per day in adults, from all sources: food, mineral waters, and supplements. Beyond that, several effects can appear:

• too high blood calcium levels;
• slowed transit;
• reduced absorption of iron and zinc;
• the formation of kidney stones in predisposed individuals.

Furthermore, a few observational studies have raised questions about high doses of isolated calcium taken as a supplement. The most consensual scientific position is to favor food, then to supplement in a targeted and moderate way.

A calcium deficiency almost never manifests where it is expected: before translating into perceptible signs, it is first read in the skeleton, which compensates silently at the expense of the bone capital.

A calcium deficiency remains silent for a long time. Since the skeleton compensates, blood calcium levels remain stable and no signal appears in the short term. The effect is read in the long term, by a progressive decrease in bone density that only a specific examination can measure.

When blood calcium itself drops, non-specific signals can appear: cramps, tingling in the extremities or around the mouth, involuntary muscle contractions. These signs have multiple possible origins. They justify a professional opinion rather than spontaneous supplementation.

In practice, the first step is often to assess your actual dietary intakes over a typical week.

Certain profiles must pay special attention to their status:

• people who exclude dairy products, especially as part of a vegan diet;
• adolescents, whose needs are the highest;
• menopausal women;
• seniors and elderly people;
• people with little sun exposure;
• heavy salt consumers;
• people following certain long-term prescriptions, such as corticosteroids.

In all these profiles, the calcium deficiency is not explained solely by the plate. It also depends on what the body manages to absorb.

On average, only 25 to 30% of dietary calcium is absorbed by the intestine. This fraction is not fixed. A study by Harvey and his collaborators, published in 1988 and conducted by measuring absorption at increasing doses, showed that the absorbed fraction decreases when the dose increases.

Calcium absorption therefore depends on the dose, the timing, and the nutrients that accompany it. It is on this ground that a large part of the benefits of calcium is played.

Vitamin D contributes to the normal absorption and use of calcium and to normal blood calcium levels. Its active form stimulates the production of channels and transport proteins that move calcium from the intestine to the blood. Without sufficient vitamin D, calcium absorption drops significantly.

However, in France, the cutaneous synthesis of vitamin D is low from October to March, due to insufficient sunlight. The combination of calcium and vitamin D is therefore a logical reflex, especially in winter.

If vitamin D lets calcium into the body, vitamin K participates in its use in the bone. It activates osteocalcin, a protein produced by osteoblasts that fixes calcium in the bone matrix. Vitamin K thus contributes to the maintenance of a normal skeletal structure.

Vitamin K2, especially in its MK-7 form, stands out for its prolonged presence in the body. A randomized double-blind placebo-controlled trial, published by Knapen and his collaborators in 2013, followed 244 menopausal women for three years. In those who received 180 µg of MK-7 per day, the evolution of bone mineral density was more favorable than under placebo.

Magnesium also contributes to the maintenance of a normal skeletal structure. It intervenes upstream: the enzymes that transform vitamin D into its active form depend on magnesium, as synthesized by a review published in 2018 by Uwitonze and Razzaque. An insufficient magnesium status can therefore limit the effectiveness of vitamin D, and by extension, calcium absorption.

The calcium and magnesium duo thus works in complementarity rather than competition.

Several food compounds reduce calcium absorption:

• Oxalates, present in spinach, sorrel, or rhubarb, form poorly soluble complexes with calcium. A study by Heaney and his collaborators, conducted using isotopic labeling in adult women, showed that only about 5% of calcium from spinach was absorbed, compared to more than 25% for that from milk.
• Phytates from whole grains and legumes produce a comparable effect. Soaking, germination, and fermentation reduce their content.
• Excess salt increases urinary calcium excretion.
• Caffeine, consumed in large quantities, has a more modest effect.
• High occasional doses also reduce effectiveness, hence the interest in spreading out intakes.

In a calcium supplement, the chemical form determines both the amount of calcium provided and its assimilation:

• Calcium carbonate is highly concentrated, with about 40% elemental calcium. It needs gastric acidity to dissolve and must therefore be taken during a meal.
• Calcium citrate is less concentrated, with about 21% elemental calcium, but its absorption depends little on stomach acidity. A meta-analysis of comparative studies published by Sakhaee and his collaborators in 1999 highlighted an absorption advantage in favor of citrate. It is particularly relevant for seniors.
• Calcium phosphate also provides phosphorus, the other component of hydroxyapatite.
• Micro-encapsulated forms coat calcium salts in a matrix, for example of lecithins or sucrose esters. The goal is to improve digestive tolerance and intestinal passage.

A pioneer of nutricosmetics in France, Biocyte has made micro-encapsulation one of its formulation axes. Comparative data remain specific to each technology: the form is judged by the studies that document it, not by its name alone.

Food remains the primary source of calcium. However, to cover your calcium needs, you must look at two things: the content of the foods and the part actually absorbed by the body.

According to the ANSES Ciqual nutritional composition table, here are some orders of magnitude:

• Cooked pressed cheese (emmental, comté, parmesan): 1,000 to 1,200 mg per 100 g, or about 300 mg for a 30 g serving.
• Milk: about 120 mg per 100 ml, or approximately 300 mg for a 250 ml bowl.
• Plain yogurt: 150 to 180 mg per pot.
• Canned sardines consumed with their bones: about 400 mg per 100 g.
• Almonds: about 250 mg per 100 g.
• Kale: 150 to 250 mg per 100 g.

Content is not everything. Cruciferous vegetables low in oxalates, such as kale or broccoli, offer excellent bioavailability, superior to that of milk according to the work of Heaney and Weaver.

Excluding dairy does not prevent you from covering your calcium needs, but requires a little organization. Several levers exist:

• Calcium mineral waters, which by definition contain more than 150 mg of calcium per liter and sometimes more than 500; a study by Heaney published in 2006 showed that this calcium was absorbed as well as that from milk
• Small fish consumed with their bones
• Cruciferous vegetables
• Whole almonds and sesame seeds
• Tofu coagulated with calcium sulfate
• Enriched plant drinks, whose label must be checked

A calcium supplement does not replace food; it complements it. It is most useful when there is a persistent gap between dietary intake and the body's needs.

A calcium supplement is justified when a persistent gap is identified between dietary intake and needs. This is often the case in the absence of dairy products, during menopause, or after age 60.

It does not replace a varied and balanced diet. It complements what food does not provide, ideally after consulting a doctor or pharmacist.

Discover our full range of mineral-rich dietary supplements to tailor your intake to your needs.

Three criteria help you choose a calcium supplement:

• The dose, which should address the actual gap rather than aiming for 1,000 mg as a rule. Moderate doses of no more than 500 mg per serving are better absorbed.
• The form, which should be suited to your tolerance and the time of intake.
• The combination with vitamin D3 and vitamin K2, which supports both the absorption and the use of calcium in the bones.

This is the approach taken by Biocyte Calcium Vitamins D3 K2. Its daily dose provides 240 mg of microencapsulated calcium (30% of the NRV), combined with vitamin D3 and vitamin K2 MK-7. Calcium and vitamins D and K help maintain normal bone structure, while vitamin D helps maintain normal calcium levels in the blood.

For those who wish to combine other minerals, Biocyte Cal/Mag/Zinc Liposomal combines calcium, magnesium, and zinc.

Before taking a calcium supplement, several points should be checked:

• Vitamin K is not recommended for people taking vitamin K antagonists without medical advice.
• Certain medications, notably thyroid hormones, may have their absorption reduced by calcium. A gap of several hours is therefore necessary, as advised by a pharmacist.
• Iron should also be taken at a different time from calcium.
• A history of kidney stones warrants prior medical advice.
• Combining several products containing calcium should be monitored to stay below the limit of 2,500 mg per day.

Biocyte Calcium Vitamins D3 K2 is not recommended for pregnant or breastfeeding women or children under 12 years of age.

• EFSA NDA Panel (2015). Scientific Opinion on Dietary Reference Values for calcium. EFSA Journal, 13(5):4101.

• EFSA NDA Panel (2012). Scientific Opinion on the Tolerable Upper Intake Level of calcium. EFSA Journal, 10(7):2814.

• ANSES (2021). Opinion on the update of nutritional references for vitamins and minerals.

• Regulation (EU) No 432/2012 establishing a list of authorised health claims relating to foods.

• Weaver CM et al. (2016). Position statement on peak bone mass development and lifestyle factors: a systematic review. Osteoporosis International, 27(4):1281-1386.

• Harvey JA, Zobitz MM, Pak CY (1988). Dose dependency of calcium absorption: a comparison of calcium carbonate and calcium citrate. J Bone Miner Res, 3(3):253-258.

• Sakhaee K et al. (1999). Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate. Am J Ther, 6(6):313-321.

• Heaney RP, Weaver CM, Recker RR (1988). Calcium absorbability from spinach. Am J Clin Nutr, 47(4):707-709.

• Heaney RP (2006). Absorbability and utility of calcium in mineral waters. Am J Clin Nutr, 84(2):371-374.

• Knapen MHJ et al. (2013). Three-year low-dose menaquinone-7 supplementation in healthy postmenopausal women. Osteoporosis International, 24(9):2499-2507.

• Uwitonze AM, Razzaque MS (2018). Role of magnesium in vitamin D activation and function. J Am Osteopath Assoc, 118(3):181-189.

• Elias PM et al. (2002). Modulations in epidermal calcium regulate the expression of differentiation-specific markers. J Invest Dermatol, 119(5):1128-136.

• Cashman MW, Sloan SB (2010). Nutrition and nail disease. Clin Dermatol, 28(4):420-425.