Needs ≈1,000–1,200 mg/day (total diet+supplement). If you supplement, ≤500 mg per dose and with vitamin D.
4-year randomized trial in postmenopausal women: 1 g/day of calcium slowed the loss of bone density compared with placebo. It supports calcium for bone, although its effect on fractures is more modest and the base is small.
View the study (study) →Prospective study (45,619 men): contrary to what was believed, higher DIETARY calcium intake was associated with FEWER kidney stones, probably because calcium binds oxalate in the gut. Observational.
View the study (study) →Cohort of 91,731 women (12 years): more calcium from FOOD was associated with fewer kidney stones, whereas calcium from SUPPLEMENTS was associated with more. It suggests preferring calcium from food; observational.
View the study (study) →⏱ 4 min read
Calcium is the most abundant mineral in the human body (about 1 kilogram in an adult), with 99 percent deposited in bones and teeth as a structural and metabolic reservoir, and the remaining 1 percent in blood and soft tissues where it performs essential functions in muscle contraction, neuromuscular transmission, blood coagulation, intracellular signaling, and other pathways; this extracellular pool is maintained within a narrow range by a complex regulatory system that includes parathyroid hormone, calcitonin, vitamin D, and renal, intestinal, and bone mechanisms, a critical homeostasis because both hypocalcemia and hypercalcemia cause serious clinical problems.
The most concentrated dietary sources are dairy products (milk, yogurt, cheese), small fish eaten with their bones (sardines, anchovies), dark leafy green vegetables (kale, broccoli, mustard greens), legumes, seeds (sesame, chia), and commercial fortified products; the recommended dietary intakes are 1,000-1,200 milligrams daily in adults depending on age, sex, and circumstances, an amount that is achievable with varied diets that include dairy but that many people with dairy restrictions or with diets low in these foods do not reach, which has historically justified population-wide supplementation.
The classic and most studied indication is the prevention and treatment of osteoporosis, especially in postmenopausal women: for decades, routine supplementation with calcium and vitamin D was the standard recommendation; however, the large intervention trials (WHI, RECORD, others) have considerably tempered the initial expectations, showing modest reductions in fractures (especially vertebral and hip) with magnitudes smaller than expected, and pointing to some specific cardiovascular safety concerns with high-dose supplements that have led to a reevaluation of the clinical strategy.
The reasonable current clinical position is to prioritize adequate dietary intake (ideally from whole foods) and reserve specific supplementation with elemental calcium (500-1,000 mg/day) for people with a documented dietary deficit, established osteoporosis, or significant risk factors, combined with adequate vitamin D; very high intakes without justification (more than 1,500 mg/day from supplements) provide no additional benefit and may carry risks.
Several meta-analyses published in the last decade have shown associations between calcium supplementation (especially without simultaneous vitamin D, especially at high doses, and especially in adults without baseline deficiency) and a modest increase in the risk of cardiovascular events, possibly attributed to accelerated vascular calcification when plasma calcium rises acutely without adequate targeting to bone (a role in which vitamin K2 and vitamin D are critical); these data are the subject of active methodological debate, but sufficient for the prevailing current clinical position to be: prioritize dietary calcium, avoid high doses of supplements without clinical justification, always combine with vitamin D, and consider K2 when supplementing specifically for bone.
In mild arterial hypertension, several trials have documented modest blood pressure reductions with calcium supplementation in people with low baseline dietary intake; in pregnancy, calcium supplementation during gestation significantly reduces the risk of preeclampsia in women with low dietary intake, an obstetric indication recognized in international guidelines for populations with calcium-poor diets.
In premenstrual syndrome, several small studies have documented significant improvements in symptom scales with supplementation at 1,000-1,200 mg/day over 3 cycles, an indication with modest clinical support and reasonable integrative use.
The recommended dietary intakes are 1,000-1,200 mg/day in adults; when supplementation is required, doses of 500-600 mg of elemental calcium per dose, divided into 2 doses with meals because absorption is saturated above 500-600 mg in a single dose; the most commonly used forms are calcium carbonate (the cheapest, requires gastric acid for optimal absorption, best with food) and calcium citrate (better absorption independent of gastric pH, the preferred option in older people with hypochlorhydria, people on proton pump inhibitors, or after bariatric surgery); calcium should be combined with adequate vitamin D to optimize absorption and bone targeting.
Generally well tolerated at usual supplemental doses; the most common adverse effects are digestive discomfort (constipation, flatulence, dyspepsia, especially with calcium carbonate); the most relevant safety consideration is plasma calcium levels with combined supplemental and dietary intake: hypercalcemia is rare with reasonable supplemental doses, but people with primary hyperparathyroidism, sarcoidosis, multiple myeloma, cancer with bone metastases, or other conditions with a risk of hypercalcemia should avoid supplementation without supervision; people with a history of calcium oxalate kidney stones should maintain adequate but not excessive intake and combine it with good hydration; those taking levothyroxine, quinolone or tetracycline antibiotics, oral bisphosphonates, and other drugs should separate doses to avoid interference with absorption; in pregnancy and breastfeeding, adequate intake is important and supplementation is reasonable in women with calcium-poor diets; cheap low-quality products may be contaminated with lead in problematic amounts, a consideration when choosing products from manufacturers with good quality controls.
Information, not medical advice. Scientific evidence reflects the quality of the studies.