Mineral
Calcium
Calcium requires 1000 mg daily for adult women and 1000 mg for men. The tolerable upper intake level is 2500 mg. It has 2 severe interactions, notably with Calcium citrate and Calcium citrate.
What Calcium does
Primary structural mineral in bone and a signalling ion in muscle and nerve function.
Absorption saturates around 500 mg per dose, so split larger intakes.
How much you need
| Measure | Adult male | Adult female |
|---|---|---|
| Recommended intake | 1000 mg | 1000 mg |
| Upper intake level | 2500 mg | |
| Typical supplement dose | 500 mg elemental · 1 cup | |
Interactions involving Calcium
11 sourced rules| Pair | Severity | Mechanism | Action |
|---|---|---|---|
| Calcium citrate × Iron bisglycinateseparate 2h | Severe | Calcium and non-heme iron compete for the same divalent metal transporter (DMT1) in the small intestine. Calcium also inhibits iron absorption directly, and the effect is proportional to dose. | Separate calcium and iron by at least 2 hours. Take iron on an empty stomach with vitamin C, and calcium with a meal later in the day.Source |
| Calcium citrate × Levothyroxineseparate 4h | Severe | Calcium binds levothyroxine in the intestinal lumen, reducing absorption by up to a third. | Separate calcium from levothyroxine by at least 4 hours. Keep the timing the same every day.Source |
| Calcium citrate × Zinc picolinateseparate 2h | Moderate | Calcium and zinc compete for overlapping intestinal transport pathways, so high doses of one reduce absorption of the other. | Space calcium and zinc by at least 2 hours, and keep zinc at or below 40 mg per day.Source |
| Iron bisglycinate × Dairy (milk, yoghurt)separate 2h | Moderate | The calcium in dairy blocks non-heme iron absorption at the same meal, and casein and whey proteins may also inhibit it. | Take iron away from dairy; use a calcium-free meal or an empty stomach as the iron window.Source |
| Calcium citrate × Tetracycline antibioticseparate 3h | Moderate | Calcium chelates tetracyclines in the intestinal lumen and reduces absorption. | Separate calcium from tetracycline by at least 2 hours.Source |
| Calcium citrate × Magnesium glycinateseparate 2h | Mild | High-dose calcium and magnesium share absorptive pathways and compete to a modest degree; the interaction is only meaningful at large supplemental doses. | If you take more than 500 mg of either, separate them by about 2 hours. Small doses together are fine.Source |
| Calcium citrate × Leafy greens | Mild | Spinach is high in oxalate, which binds calcium in the gut and makes that plant calcium largely unavailable. | Do not count spinach as a calcium source. Take supplemental calcium away from high-oxalate meals.Source |
| Dairy (milk, yoghurt) × Levothyroxineseparate 4h | Mild | The calcium in milk binds levothyroxine; even a splash in the coffee you take it with lowers absorption. | Take levothyroxine with plain water only, at least 30-60 minutes before breakfast.Source |
| Calcium citrate × ACE inhibitor | Mild | Calcium supplements may slightly attenuate the blood-pressure effect of ACE inhibitors, though the clinical significance is small. | No action needed at standard doses; keep calcium consistent.Source |
| Calcium citrate × Metformin | Synergy | Calcium is required for the intrinsic factor-B12 receptor complex; adequate calcium partially protects B12 absorption on metformin. | Ensure adequate calcium intake while on metformin, ideally from food.Source |
| Calcium citrate × Vitamin D3 softgel | Synergy | Vitamin D drives active calcium absorption in the small intestine via calbindin. Without adequate vitamin D, calcium supplementation is far less effective and may not reach bone. | Take calcium with vitamin D3, and keep calcium doses at or below 500 mg at a time for absorption.Source |