Calcium
Contributes to the maintenance of normal bones and teeth, and to normal muscle function.
Also known as Calcium Citrate, Calcium Carbonate, Cal, Calcium Hydroxyapatite
Common doses
500-1000 mg
Best timing
Any time
Food
Take with food
Interactions
8 known
Calcium is the most abundant mineral in the body, with 99% stored in bones and teeth. It is essential for bone structure, muscle contraction, nerve signalling, blood clotting, and hormone secretion. Calcium is also one of the most supplemented minerals, particularly among postmenopausal women for osteoporosis prevention.
However, calcium supplementation has become more nuanced in recent years. Several large studies have raised questions about whether calcium supplements (as opposed to dietary calcium) may increase cardiovascular risk by promoting arterial calcification. This concern is one of the reasons why Vitamin K2 is often recommended alongside calcium and Vitamin D.
Calcium has more absorption interactions with other supplements than almost any other mineral. It inhibits iron, zinc, manganese, and chromium absorption. Timing your calcium supplement away from these minerals is essential.
Key benefits
Bone health
Calcium is needed for the maintenance of normal bones and teeth. Adequate calcium intake is critical during growth, pregnancy, and to prevent osteoporosis.
Muscle function
Calcium contributes to normal muscle function. It is required for muscle contraction via the actin-myosin mechanism.
Nerve function
Calcium contributes to normal neurotransmission. It is essential for nerve signal propagation.
Blood clotting
Calcium contributes to normal blood clotting. Multiple coagulation factors are calcium-dependent.
Available forms
Calcium Citrate
Well-absorbed even on an empty stomach. Does not require stomach acid. Preferred for people on acid-reducing medications.
Calcium Carbonate
The cheapest and most common form. Contains 40% elemental calcium but requires stomach acid for absorption. Take with meals.
Calcium Hydroxyapatite
Derived from bone. Contains calcium and phosphorus in their natural bone ratio. Some evidence for superior bone integration.
Food sources
- Dairy (milk, yogurt, cheese)
- Sardines with bones
- Fortified plant milks
- Kale and broccoli
- Tofu (calcium-set)
- Almonds
Signs of deficiency
- Muscle cramps and spasms
- Numbness in hands and feet
- Weak, brittle nails
- Easy fracturing of bones
- Dental problems
- Fatigue
Upper intake limit
2,500 mg/day from all sources (NIH). Most guidelines now recommend getting calcium primarily from food, with supplements only to fill gaps. Split supplement doses to 500 mg or less per serving for better absorption.
Research summary
Strong evidence for bone health when combined with Vitamin D. The cardiovascular concern (calcium supplements and arterial calcification) has been raised by several meta-analyses but remains debated. Adding Vitamin K2 may direct calcium to bones instead of arteries. Current thinking favours food-first calcium with supplements only to fill dietary gaps.
Known interactions (8)
Calcium blocks iron absorption significantly
Calcium may reduce zinc absorption
Calcium and magnesium compete at high doses
Calcium may reduce manganese absorption
Calcium carbonate may interfere with chromium
High caffeine intake modestly increases calcium loss
Vitamin D is essential for calcium absorption
Potassium may actually help preserve calcium
Check your full stack
for interactions.
See what competes, what combines well, and when to take everything. Every interaction cites a published source.
Stack
6 supplements
Stack review
1 flagZinc and Iron compete for the same absorption pathway. Take at least 2 hours apart.
Supplements
This information is for educational purposes only. It is not medical advice and does not diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional.