Calcium

Essential macromineral critical for bone health, muscle function, nerve transmission, and numerous cellular processes

Scientific nameCalcium (Ca) FormulaCa Molecular weight40.08 g/mol CAS7440-70-2

30 absorption score

8 safety / 10

20 USD per month

100 elemental calcium %

6 documented interactions

Check it against something

Evidence level A

Calcium with:

72 out of 100

Needs attention Separate by 2-4 hours to avoid the interaction below.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Bone health and osteoporosis prevention

Essential for bone formation, maintenance, and prevention of bone loss

Primary structural component of bones and teeth, stimulates osteoblast activity Evidence A-grade 6-12 months for bone density improvements

Muscle function and contraction

Critical for proper muscle contraction and relaxation

Enables actin-myosin interaction and regulates muscle fiber excitation Evidence A-grade Immediate for muscle function

Nerve transmission and neurological function

Essential for proper nerve signal transmission and neurotransmitter release

Regulates neurotransmitter release and nerve impulse conduction Evidence A-grade Immediate for nerve function

Cardiovascular health and blood pressure regulation

Supports healthy blood pressure and cardiovascular function

Regulates vascular smooth muscle contraction and blood vessel function Evidence B-grade 4-12 weeks for cardiovascular benefits

Blood clotting and wound healing

Essential cofactor for blood coagulation and proper wound healing

Required for several steps in the coagulation cascade Evidence A-grade Immediate for clotting function

Others take these for the same thing

Same goal, different mechanism — check any of them against this one

Creatine Monohydrate Strength & power enhancement 3-5g A 95% Turmeric Anti-inflammatory & antioxidant 300-1000mg A 3% Magnesium Glycinate Superior absorption sleep & muscle support 200-600 mg A 90% Vitamin D3 Bone health & immune support 1000-2000 IU A 85% Collagen Peptides Skin health & joint support 5-15g B 85% Calcium Carbonate Affordable bone health & antacid 1000-1200 mg A 25%

Or a different form of the same thing

the comparison people search most

Calcium vs Calcium Carbonate absorption 30 against 25 · $20 against $10 a month 25% Calcium vs Calcium Citrate absorption 30 against 45 · $20 against $20 a month 45% Calcium vs Calcium Hydroxyapatite absorption 30 against 40 · $20 against $60 a month 40%

All Calcium forms ranked by absorption →

Every pair we checked

12 combinations scored by the engine

Calcium + Whey Protein Very high calcium may interfere with protein absorption Needs attention 61

Calcium + Caffeine No documented interaction either way No known interaction 70

Calcium + Creatine Monohydrate No documented interaction either way No known interaction 70

Calcium + Calcium Carbonate No documented interaction either way No known interaction 70

Calcium + Bovine Collagen No documented interaction either way No known interaction 70

Calcium + DHA No documented interaction either way No known interaction 70

Calcium + Turmeric No documented interaction either way No known interaction 70

Calcium + Fish Oil (EPA/DHA) No documented interaction either way No known interaction 70

Calcium + Vitamin D3 Reduces vitamin D conversion efficiency Needs attention 72

Calcium + Magnesium Oxide High calcium can interfere with magnesium absorption Needs attention 76

Calcium + Lactase Enhanced calcium absorption from dairy sources Works better together 82

Calcium + Vitamin C (Ascorbic Acid) Dramatically improves calcium absorption and bone health Works better together 90

Dosage

Divided doses with meals

Daily1,000-1,200 mg

Bone health1,000-1,200 mg daily

Osteoporosis prevention1,200-1,500 mg daily

Children teens700-1,300 mg daily based on age

Pregnancy lactation1,000-1,300 mg daily

Upper limit 2500 mg NIH ODS

Before you take it

VeganYes

When to expect it

First EffectsImmediate for muscle and nerve function

Peak Benefits6-12 months for bone density improvements

Deficiency DevelopmentWeeks to months for functional deficiency

Toxicity OnsetChronic high intake over months to years

How to measure it

$50-100

MarkerSerum calcium, ionized calcium, parathyroid hormone (PTH)

Optimal8.5-10.5 mg/dL total, 4.5-5.5 mg/dL ionized

Deficient below<8.5 mg/dL total calcium, elevated PTH

FrequencyAnnually or when assessing bone health

What people actually reported to the FDA

CAERS, 569 reports naming it as the suspect

Most reported effects

Dyspnoea 58

Vomiting 33

Excluded from the list above: choking (207), dysphagia (71), foreign body trauma (54), foreign body (33). Those are people struggling with the tablet itself, not with the compound.

Named as the suspect 569 reports of 1,000+ that mention it at all

Serious outcome 89% hospitalisation, emergency room or worse

Other Serious or Important Medical Event468

Hospitalization82

Visited a Health Care Provider63

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not

Elemental calcium 100% of 40.08 g/mol

Absorption Low 30 of 100 · poorly absorbed relative to other forms

Delivered daily 330 mg

Cost per 100 mg delivered $0.20 comparative — uses the absorption score, not a measured percentage

A 500 mg capsule of Calcium contains 500 mg of calcium. How much of that crosses into your blood is not measured for this form — the absorption score ranks it against other forms, it is not a share of the dose. How this is calculated →

Works better with

3 documented

Vitamin D

Dramatically improves calcium absorption and bone health

Vitamin D increases intestinal calcium absorption and bone mineralization · level A

Vitamin K2

Directs calcium to bones and prevents arterial calcification

K2 activates osteocalcin and matrix Gla protein for proper calcium utilization · level B

Magnesium

Essential for calcium metabolism and bone health

Magnesium regulates calcium transport and parathyroid hormone function · level A

What not to take with Calcium

3 documented

Excessive Phosphorus

High phosphorus intake may impair calcium absorption

Disturbs calcium-phosphorus balance and increases calcium excretion · moderate significance

Phytic Acid Oxalates

Plant compounds that bind calcium and reduce absorption

Form insoluble complexes preventing calcium absorption · moderate significance

Excessive Sodium

High sodium intake increases calcium excretion through urine

Sodium and calcium compete for reabsorption in kidneys · moderate significance

Medication interactions

Discuss these with a pharmacist before combining

bisphosphonates Major

Calcium significantly reduces bisphosphonate absorption

What to do: Separate doses by at least 2 hours

thyroid-medications Moderate

Calcium reduces absorption of levothyroxine and similar drugs

What to do: Separate doses by 4+ hours

antibiotics-quinolones Major

Calcium significantly reduces antibiotic effectiveness

What to do: Separate doses by 2-6 hours depending on antibiotic

Available forms

bioavailability compared

Ranks 3 of 4 among calcium forms. Calcium Citrate absorbs better — 45%. Compare all forms →

Calcium carbonate 35

Calcium citrate 45

Calcium phosphate 30

Calcium carbonate: High elemental calcium, Inexpensive, Well-studied, Widely available

Calcium citrate: Better absorption, No acid needed, Can take empty stomach, Less GI upset

Calcium phosphate: Provides phosphorus too, Good for bone health, Natural bone mineral, Well-tolerated

Food sources

before you supplement

Dairy products (milk, cheese, yogurt) 200-300 mg per serving · 30

Leafy greens (kale, collards, bok choy) 100-200 mg per cup · 50

Canned fish with bones (sardines, salmon) 200-400 mg per serving · 35

Fortified foods (plant milks, tofu, orange juice) 200-500 mg per serving · 25

Too little

deficiency signs

Bone-related symptoms:
Osteoporosis, osteopenia, and increased fracture risk
Dental problems including tooth decay and gum disease
Muscle cramps, spasms, and tetany
Numbness and tingling in fingers and toes
Abnormal heart rhythms and cardiovascular issues
Increased bleeding tendency and poor wound healing

Too much

toxicity signs

Calcium excess symptoms (hypercalcemia):
Kidney stones and nephrocalcinosis
Constipation and gastrointestinal upset
Interference with iron, zinc, and magnesium absorption
Arterial calcification and cardiovascular risk
Kidney dysfunction and calcium deposits in soft tissues

Who benefits most

postmenopausal-women

High risk for osteoporosis due to estrogen decline

1,200 mg daily with cofactors

children-adolescents

Critical period for peak bone mass development

700-1,300 mg daily based on age

elderly-adults

Increased calcium needs and decreased absorption with aging

1,200 mg daily with vitamin D

vegans-dairy-free

Limited dietary calcium sources from plant-based diets

1,000-1,200 mg daily

athletes-high-impact

Increased calcium needs for bone stress adaptation

1,000-1,500 mg daily

Where to buy it

compare forms first

Look for Calcium at 1,000-1,200 mg per serving. The form that matters here is Calcium carbonate.

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What else affects it

Beyond other supplements

Excessive phosphorus

High phosphorus intake may impair calcium absorption

Disturbs calcium-phosphorus balance and increases calcium excretion

Phytic acid oxalates

Plant compounds that bind calcium and reduce absorption

Form insoluble complexes preventing calcium absorption

Excessive sodium

High sodium intake increases calcium excretion through urine

Sodium and calcium compete for reabsorption in kidneys

How it works

Primary structural component providing rigidity and strength to bones and teeth
Essential cofactor for muscle contraction through actin-myosin interaction
Regulates nerve impulse transmission and neurotransmitter release
Required for blood coagulation cascade and proper wound healing
Maintains cellular membrane integrity and permeability
Activates numerous enzymes involved in energy metabolism

Key findings

what the evidence supports

Essential for bone health with overwhelming evidence for osteoporosis prevention
Optimal absorption requires vitamin D, magnesium, and proper dosing strategy
Benefits maximize when combined with weight-bearing exercise
Safety excellent at recommended doses with appropriate cofactors

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of Calcium?

Documented effects: Bone health and osteoporosis prevention; Muscle function and contraction; Nerve transmission and neurological function; Cardiovascular health and blood pressure regulation. Essential for bone formation, maintenance, and prevention of bone loss

How much Calcium should you take per day?

The common daily range is 1,000-1,200 mg. By goal — bone health: 1,000-1,200 mg daily; osteoporosis prevention: 1,200-1,500 mg daily; children teens: 700-1,300 mg daily based on age; pregnancy lactation: 1,000-1,300 mg daily.

When is the best time to take Calcium?

Divided doses with meals. First effects are typically reported within Immediate for muscle and nerve function.

What are the side effects of Calcium?

At excessive doses: Calcium excess symptoms (hypercalcemia):, Kidney stones and nephrocalcinosis, Constipation and gastrointestinal upset, Interference with iron, zinc, and magnesium absorption, Arterial calcification and cardiovascular risk. Safety rating at normal doses is 8 out of 10.

What should you not take with Calcium?

Separate it from Excessive Phosphorus, Phytic Acid Oxalates, Excessive Sodium by two to four hours. High phosphorus intake may impair calcium absorption

Does Calcium interact with medications?

Documented interactions with bisphosphonates, thyroid-medications, antibiotics-quinolones. Discuss these with a pharmacist before combining.

How much Calcium is too much?

The tolerable upper intake level is 2500 mg per day for adults, per NIH ODS. Above that, the risk of adverse effects rises: Calcium excess symptoms (hypercalcemia):, Kidney stones and nephrocalcinosis, Constipation and gastrointestinal upset.

How do you know if you need Calcium?

The marker is Serum calcium, ionized calcium, parathyroid hormone (PTH), optimal range 8.5-10.5 mg/dL total, 4.5-5.5 mg/dL ionized. Common deficiency signs: Bone-related symptoms:, Osteoporosis, osteopenia, and increased fracture risk, Dental problems including tooth decay and gum disease, Muscle cramps, spasms, and tetany.

Taken for

38 Joints & Bones

Vitamin D3 · Calcium Carbonate · Bovine Collagen

43 Performance

Caffeine · Creatine Monohydrate · Whey Protein