What does calcium do in the body?

Calcium supports bone and tooth structure and is needed for muscle contraction, nerve signaling, and normal blood vessel function.

How much calcium do adults typically need per day?

Many adults aim for about 1000–1200 mg per day from food and supplements combined, depending on age and sex. Individual needs can vary.

What are good food sources of calcium?

Common sources include dairy products, calcium-set tofu, canned fish with bones, leafy greens, and calcium-fortified foods and beverages.

Should I take calcium with vitamin D?

Vitamin D helps the body absorb calcium, so adequate vitamin D status supports calcium use. Some people take them together if dietary intake or sun exposure is low.

Are there side effects or interactions with calcium supplements?

Calcium supplements can cause constipation or stomach upset in some people. Calcium can interfere with absorption of certain medicines and minerals, so spacing doses may be needed.

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Vitamin B

Vitamin B1 (Thiamine)

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Vitamin B5 (Pantothenic Acid)

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Trimethylglycine (Betaine)

NMN (Nicotinamide Mononucleotide)

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D-Chiro-Inositol

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Betaine HCL

Nicotinamide Riboside

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Choline

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Calcium

Calcium Alpha-Ketoglutarate

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Magnesium Bisglycinate

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Calcium

Strong study situation·10/10

A higher score indicates better study conditions, but not necessarily effectiveness.

Calcium is an essential mineral supporting bone health, muscle function, and nerve signaling; supplementation may help those at risk of dietary insufficiency.

Cardiovascular Support Essential Nutrient Bone Health

dose range

1000–1200 mg

Usually divided into 500–600 mg per dose, not exceeding 1000–1200 mg/day from supplements.

Consumption

Take with food if using calcium carbonate; calcium citrate can be taken with or without food. Prefer food sources when possible.

Not fat-soluble.

Best time

Split higher daily doses to improve absorption and reduce gastrointestinal side effects. Take at different times from medications with which calcium interacts.

Description

Calcium is the most abundant mineral in the body, vital for bone and dental health, muscle contraction, nerve transmission, and supporting vascular and hormonal functions.

benefits

Main effects with level of evidence

Strong

Note on evidence

Extensive evidence supports calcium’s role in bone and tooth health, with supplementation beneficial for at-risk groups; benefits for cardiovascular or other outcomes are less clear.

Supports bone health and prevents osteoporosis

Strong

Adequate calcium intake is critical for building and maintaining strong bones, reducing osteoporosis risk, and minimizing age-related bone loss—especially in postmenopausal women and older adults.

Particularly relevant for: older adults · postmenopausal women

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S2 · PubMed - Meta-analysis: Calcium supplementation and bone density S3 · EFSA Journal: Scientific Opinion on Dietary Reference Values for Calcium S4 · Cochrane Review: Calcium supplementation for prevention of bone loss

Contributes to muscle function and nerve signaling

Strong

Calcium enables normal muscle contraction (including the heart) and proper nerve impulse transmission.

Particularly relevant for: general

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S5 · Examine.com: Calcium

May help maintain normal blood pressure and vascular health

Mixed

Adequate calcium, particularly from food, may support blood pressure regulation and vascular function; supplemental calcium’s effect on cardiovascular risk is less established and may be neutral or, in excess, adverse.

Particularly relevant for: general

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S7 · PubMed: Calcium and cardiovascular risk S6 · Harvard T.H. Chan School of Public Health: Calcium

Safety & Information

Important safety information & known risks

For educational purposes only • not medical advice

Calcium is generally safe at recommended doses, but excessive intake or certain conditions can pose risks.

warning notices

Constipation and mild gastrointestinal discomfort are common minor side effects at higher doses.
Prolonged excessive intake can lead to hypercalcemia, kidney stones, and may increase cardiovascular risk, especially in susceptible populations.
People with chronic kidney disease, hyperparathyroidism, hypercalcemia, or a history of kidney stones should avoid supplementation unless under physician supervision.
Avoid calcium supplements if you have hypercalcemia or significant kidney impairment, unless directed by a physician.
Avoid co-administration with certain antibiotics (e.g., tetracyclines, fluoroquinolones) or thyroid medications, as calcium may reduce absorption.
Monitor total calcium intake (diet plus supplements) to avoid exceeding 2000–2500 mg daily, which increases risk of kidney stones and hypercalcemia, especially in older adults, those with renal dysfunction, or those using high-dose vitamin D.
Use caution with calcium supplementation if you have a history of kidney stones or are at high cardiovascular risk.

Known interactions with medications

Tetracyclines and fluoroquinolone antibiotics
Thyroid hormone (levothyroxine)
Certain anticonvulsants (e.g., phenytoin)

Contraindications / special precautions

Severe kidney disease
Hypercalcemia
Unmanaged hyperparathyroidism

interactions

Important interactions between active ingredient ↔ supplement / medication / food

Calcium interacts with several nutrients and medications, affecting absorption and biological effects.

Vitamin D increases calcium absorption and effectiveness.

nutrient · Vitamin D

PairStrongTake together

Why

Vitamin D stimulates intestinal absorption of calcium, supporting bone health.

recommendation

Consider pairing with vitamin D, especially in populations at risk for deficiency.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S5 · Examine.com: Calcium

Calcium may reduce absorption of iron when taken together.

nutrient · Iron

SeparateModerateSeparate by 2h

Why

Divalent minerals like calcium can compete with iron for absorption sites in the intestine.

recommendation

Separate calcium and iron supplements by at least 2 hours.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S5 · Examine.com: Calcium

High doses of calcium may interfere with magnesium absorption.

nutrient · Magnesium

CautionMixedApplies mainly to high-dose supplements (>800 mg) taken at once.

Why

Large doses of calcium may reduce magnesium uptake in the gut if consumed together.

recommendation

Ensure adequate intake of both, particularly if supplementing for extended periods; separate if high doses used.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S5 · Examine.com: Calcium

Calcium binds tetracycline and similar antibiotics, reducing their effectiveness.

drug · Tetracycline antibiotics

AvoidStrongSeparate by 2–4h

Why

Calcium chelates with certain antibiotics, impairing their absorption.

recommendation

Avoid taking calcium supplements within 2–4 hours of these antibiotics.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S8 · FDA Drug Interactions with Calcium

Calcium can reduce the absorption of thyroid hormone medications (e.g., levothyroxine).

drug · Levothyroxine

AvoidStrongSeparate by 4h

Why

Calcium supplements may bind these medications in the gut, reducing absorption.

recommendation

Take calcium and thyroid medications at least 4 hours apart.

S8 · FDA Drug Interactions with Calcium S9 · Mayo Clinic: Calcium Supplements

mechanisms of action

Brief explanations of how it works

Bone mineralization

Calcium is the primary mineral deposited in bones, forming hydroxyapatite crystals that provide structure and strength.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S3 · EFSA Journal: Scientific Opinion on Dietary Reference Values for Calcium

Muscle contraction and nerve signaling

Calcium ions enable excitation-contraction coupling in muscle fibers and facilitate neurotransmitter release at nerve synapses.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet S5 · Examine.com: Calcium

Second messenger in cell signaling

Calcium acts as a cell signaling molecule involved in hormone secretion and numerous metabolic pathways.

S1 · NIH Office of Dietary Supplements: Calcium Fact Sheet

Sources & References

Primary literature and reviews on which these statements are based

9 sources

NIH Office of Dietary Supplements: Calcium Fact Sheet

PubMed - Meta-analysis: Calcium supplementation and bone density

EFSA Journal: Scientific Opinion on Dietary Reference Values for Calcium

Cochrane Review: Calcium supplementation for prevention of bone loss

Examine.com: Calcium

Harvard T.H. Chan School of Public Health: Calcium

PubMed: Calcium and cardiovascular risk

FDA Drug Interactions with Calcium

Mayo Clinic: Calcium Supplements

Last updated: February 8, 2026

This information is for educational purposes only and does not replace medical advice.