Calcium – The Mineral for Bones, Muscles, and the Nervous System

Calcium is the most abundant mineral in the human body. Over 99% of it is stored in bones and teeth, but the remaining 1% in the blood and cells is essential for vital functions ranging from muscle contraction to blood clotting.

Functions of Calcium in the Body

Bones and Teeth: Primary structural component together with phosphate (hydroxyapatite)
Muscle Contraction: Calcium ions bind to troponin, enabling actin-myosin interaction
Nerve Signals: Vesicle fusion and neurotransmitter release are calcium-dependent
Blood Clotting: Calcium is a cofactor for several clotting factors (Factor IV)
Hormone Synthesis: Involved in insulin secretion and other endocrine processes
Cellular Signal Transduction: Second messenger function in numerous signaling pathways

Calcium Homeostasis

Blood calcium levels are strictly regulated (2.2–2.6 mmol/l). Three hormones control this balance:

PTH (Parathyroid Hormone): Increases calcium through bone resorption, renal reabsorption, and vitamin D activation
Calcitriol (active Vitamin D): Enhances intestinal absorption and renal reabsorption
Calcitonin: Lowers calcium by inhibiting bone resorption (in hypercalcemia)

Bioavailability and Influences

Factor	Effect on Absorption
Vitamin D3	Essential – strongly increases calcium transporters (TRPV6) in the gut
Magnesium	Synergistic – necessary for PTH action
Vitamin K2	Directs calcium to bones, prevents deposition in arteries
Phytates, Oxalates	Inhibit absorption (spinach, whole grains)
High Protein Doses	Increase renal calcium excretion
Caffeine, Alcohol	Increase excretion

Daily Requirement and Sources

Group	DGE Recommendation
Adults (19–50 yrs)	1,000 mg/day
Over 50 years	1,000–1,200 mg/day
Pregnant/Lactating	1,000–1,200 mg/day
Adolescents (13–18 yrs)	1,200 mg/day (bone building phase)

Food Sources (Calcium Content/100g)

Food	Calcium	Bioavailability
Parmesan	1,184 mg	~32 %
Poppy Seeds (dry)	1,448 mg	Low (oxalates)
Kale	157 mg	~49 % (high!)
Whole Milk	120 mg	~32 %
Broccoli	47 mg	~61 %
Almonds	264 mg	~21 %

Comparison of Supplement Forms

Form	Elemental Calcium	Bioavailability	Special Features
Calcium Carbonate	40 %	Good (with meals)	Inexpensive, requires stomach acid
Calcium Citrate	21 %	Very good (can be taken on an empty stomach)	For older adults, PPI users
Calcium Gluconate	9 %	Good	Low concentration
Calcium Bisglycinate	~13 %	Very high	Best tolerability

The Calcium Paradox

High calcium intake from supplements increases cardiovascular risk in some studies – in cases of concomitant vitamin K2 deficiency, calcium is deposited in arterial walls instead of bones. The solution: always take calcium in combination with sufficient vitamin D3 and K2 (MK-7).

Frequently Asked Questions (FAQ)

Can I take calcium and iron at the same time?

No – calcium significantly inhibits iron absorption. Maintain at least a 2-hour interval between supplements.

Is more calcium always better for bones?

No. Without vitamin D and K2, as well as sufficient exercise, stable bone cannot be built. Excess can even be harmful.

Which calcium form for vegans?

Calcium citrate or algal calcium (from sea algae) are good plant-based alternatives. Supplement well with calcium-rich plants such as kale, broccoli, sesame.