🧬 Family & Essentiality

🌿 Plain-Language Summary

Calcium is the most abundant mineral in the body, crucial for bone and teeth strength. It also plays vital roles in muscle contraction, nerve transmission, and blood clotting. Vitamin D status strongly influences how well calcium is absorbed and used.

⚗️ Molecular & Chemical IDs

• Element: Ca (Calcium)
• Atomic number: 20
• Common supplement salts: carbonate, citrate, phosphate, lactate

⚡ Functions

• Structural: bone and teeth mineralisation with phosphate (hydroxyapatite)
• Cell signalling: required for muscle contraction and neurotransmission
• Blood clotting: essential cofactor in the coagulation cascade
• Hormonal roles: involved in secondary messenger systems

🍽️ Absorption & Bioavailability

🥗 Food Sources

• Dairy: milk, yoghurt, cheese (major contributors in Australia)
• Fish with edible bones: e.g., sardines, salmon
• Fortified plant milks (check labels for calcium content)
• Tofu set with calcium salts
• Leafy greens: bok choy and kale absorbed better than spinach (high oxalate reduces absorption)

🇦🇺 Australian NRVs (NHMRC)

• RDI (Adults 19–50 yrs): 1000 mg/day
• RDI (Women 51+ & Men 70+): 1300 mg/day
• UL (Adults): 2500 mg/day

🚨 Deficiency & Excess

Deficiency / Low Status

Over time may contribute to osteopenia, osteoporosis, and fracture risk. Can cause muscle cramps and secondary hyperparathyroidism if chronically low.

Excess

Usually from high-dose supplements. Risks include hypercalcaemia, kidney stones, and constipation.

🧪 Testing & Monitoring

• Serum calcium (albumin-corrected) and ionised calcium
• 25-hydroxyvitamin D and parathyroid hormone (PTH) if deficiency suspected
• Urinary calcium assessment in selected cases (e.g., stone formers)

🔄 Interactions

• Thiazide diuretics ↑ serum calcium; loop diuretics ↓ calcium
• Iron, zinc, and some antibiotics can bind with calcium — separate dosing
• Synergistic with vitamin D and vitamin K₂ for bone and vascular health

📊 Evidence Snapshot

• 🔬✅ Well-established: Critical for bone strength, prevention and management of hypocalcaemia
• 🧪⚖️ Mixed: Fracture reduction benefits from supplementation are less clear in healthy, replete adults
• ⚠️❌ Unproven/hype: Broad claims for weight loss or cardiovascular protection at high supplemental intakes