Calcium
The parathyroid hormone (PTH) is an important regulator of calcium metabolism. If dietary calcium isn't sufficient, causing blood calcium to decrease, the PTH increases, and removes calcium from bones to maintain a normal amount in the blood. PTH has many other effects, contributing to inflammation, calcification of soft tissues, and decreased respiratory energy production.[1]
| Calcium | |
|---|---|
| [[File:|250px]] | |
| Chemical formula | Ca |
| Molar mass | 40.078 g/mol |
| Color | Silvery-white metallic (pure metal) |
| Hardness (Mohs) | 1.75 (very soft – can be cut with a knife) |
| Density | 1.55 g/cm³ (at 20 °C) |
| Solubility | Reacts vigorously with water → forms Ca(OH)₂ + H₂ gas
Insoluble in organic solvents Calcium ions (Ca²⁺) are highly soluble in water when paired with appropriate anions |
| Bioavailability | Best: calcium citrate (≈ 30–35 % absorbed)
Good: calcium citrate-malate, calcium lactate Moderate: calcium carbonate (≈ 20–30 %, needs stomach acid) Lower: calcium phosphate, calcium gluconate Very low: calcium from spinach/oxalate-rich plants (only ≈ 5 %) |
| Dietary sources | Best sources (high content + good absorption):
• Dairy (milk, yogurt, cheese) • Small bony fish (sardines, canned salmon with bones) • Kale, broccoli, bok choy (low-oxalate greens) • Fortified orange juice Moderate/lower absorption sources: • Almonds, sesame seeds/tahini, chia seeds • Beans, lentils • Figs, oranges • Spinach, Swiss chard, beet greens (high oxalate → poor absorption) |
| RDA (adults 19–50 y) | 1,000 mg elemental calcium per day |
| Upper limit | 2,000–2,500 mg/day (depending on age) |
