Calcium
Calcium is a major mineral required for bones, teeth, muscle contraction, nerve transmission, vascular function, and blood clotting.
Overview
Biological role
Most body calcium is stored in bones and teeth; the remainder supports muscle contraction, nerve signaling, blood clotting, enzyme activity, and vascular contraction and dilation.
Mechanism of action
Calcium functions as a structural mineral in hydroxyapatite and as a regulated intracellular and extracellular signaling ion. Vitamin D, parathyroid hormone, and calcitonin regulate calcium balance.
Chemical forms
Dietary calcium salts; supplement forms include calcium carbonate and calcium citrate.
Quick answers before choosing a supplement
Chemical forms and absorption
Common forms
Dietary calcium salts; supplement forms include calcium carbonate and calcium citrate.
Absorption context
Calcium carbonate is best absorbed with food, while calcium citrate can be taken with or without food. High oxalate and phytate foods can reduce calcium absorption from those foods.
Clinical use
Calcium works with vitamin D and physical activity for bone health. Supplement decisions should consider total dietary calcium, not supplements alone.
Absorption and action pathway
What to take with, and what to avoid
Works Well With
Avoid / Use Caution
Best time to take
Frequently asked questions
When is the best time to take Calcium?
Use with meals if the supplement irritates the stomach; separate from medicines or competing minerals when needed.
Can Calcium be taken with coffee or milk?
Some minerals compete with foods, drinks, or medicines. Separate timing is useful when treating a deficiency.
Who should be careful with Calcium?
Adolescents, postmenopausal women, older adults, people avoiding dairy, and people with malabsorption may require dietary assessment.
Food and Intake
| Age / group | Male | Female | Pregnancy | Lactation | Upper limit |
|---|---|---|---|---|---|
| 1-3 years | 700 | 700 | – | – | UL 2,500 |
| 4-8 years | 1,000 | 1,000 | – | – | UL 2,500 |
| 9-18 years | 1,300 | 1,300 | 1,300 | 1,300 | UL 3,000 |
| 19-50 years | 1,000 | 1,000 | 1,000 | 1,000 | UL 2,500 |
| 51-70 years | 1,000 | 1,200 | – | – | UL 2,000 |
| 71+ years | 1,200 | 1,200 | – | – | UL 2,000 |
International reference intake comparison
| Country / authority | Common reference value |
|---|---|
| USA / NIH-FNB | RDA 1,000 mg most adults; 1,200 mg in women 51+ and adults 71+ |
| Europe / EFSA | PRI adults 950 mg |
| Australia-New Zealand / NRV | RDI 1,000 mg adults; higher in adolescents/older adults |
| Thailand / Thai FDA | Thailand: use Thai RDI and Thai FDA / Ministry of Public Health regulations for labeling and supplement products. Do not interpret labeling values as therapeutic doses; product-specific limits must be checked against the latest notification and formula. |
This table compares reference-intake frameworks across authorities. Values may use different terms such as RDA, AI, PRI, or NRV and should not be merged into one universal dose.
Food source comparison for Calcium
| Food | Serving amount | Calcium | %DV | %DV bar | Servings to reach 1,000 mg |
|---|---|---|---|---|---|
| plain yogurt | 8 oz | 415 mg | 42% | 2 | |
| calcium-fortified orange juice | 1 cup | 349 mg | 35% | 3 | |
| mozzarella cheese | 1.5 oz | 333 mg | 33% | 3 | |
| sardines with bones | 3 oz | 325 mg | 33% | 3 | |
| milk | 1 cup | 300 mg | 30% | 3 | |
| calcium-set tofu | 1/2 cup | 253 mg | 25% | 4 |
Food values are practical comparison values. Actual content varies by variety, preparation, fortification, and serving size.
Safety
Deficiency
Long-term inadequate intake contributes to low bone mass and osteoporosis risk. Acute hypocalcemia is usually related to medical conditions and can cause neuromuscular symptoms.
Excess and toxicity
Excess calcium can cause constipation, kidney stones, hypercalcemia, renal insufficiency, and impaired absorption of iron and zinc.
Precautions
People with kidney disease, hypercalcemia, kidney stones, or high calcium intake from supplements should seek clinical guidance.
Special populations
Adolescents, postmenopausal women, older adults, people avoiding dairy, and people with malabsorption may require dietary assessment.
Fast risk map
LOW: insufficient intake
Long-term inadequate intake contributes to low bone mass and osteoporosis risk. Acute hypocalcemia is usually related to medical conditions and can cause neuromuscular symptoms.
UL: excess intake
Excess calcium can cause constipation, kidney stones, hypercalcemia, renal insufficiency, and impaired absorption of iron and zinc.
Precautions: interactions and timing
People with kidney disease, hypercalcemia, kidney stones, or high calcium intake from supplements should seek clinical guidance.
SP: special populations
Adolescents, postmenopausal women, older adults, people avoiding dairy, and people with malabsorption may require dietary assessment.
Interactions and Clinical Context
Drug interactions
ODS lists interactions with dolutegravir, levothyroxine, lithium, quinolone antibiotics, tetracycline antibiotics, and thiazide diuretics. Calcium can reduce absorption of some medicines when taken together.
Food interactions
Calcium carbonate is best absorbed with food, while calcium citrate can be taken with or without food. High oxalate and phytate foods can reduce calcium absorption from those foods.
Clinical notes
Calcium works with vitamin D and physical activity for bone health. Supplement decisions should consider total dietary calcium, not supplements alone.
Evidence level
High for essentiality, bone role, RDA, UL, and drug-interaction precautions.