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Place · Level 3
99% 在骨头里 · 1% 调节心跳与肌肉收缩 · 严格被激素管着
synergy · 5
Calcium contracts muscle; magnesium relaxes it. Both needed in balance.
Bone mineral is calcium phosphate; bone health is not calcium alone.
Counterintuitive: high *dietary* calcium (800-1200 mg/d) binds oxalate in the gut → oxalate absorption ↓ → calcium-oxalate stone risk ↓ 35-50% (Curhan 1993/1997). But high *supplemental* calcium taken without food raises risk. The distinction: food-calcium-with-meals.
Fluoride supports enamel remineralization alongside calcium-phosphate mineral.
High K (especially K-citrate) reduces urinary calcium loss → indirect bone protection; the DASH-bone overlap. Opposite to high-sodium calciuresis — K offsets Na's bone tax.
cofactor · 5
Severe hypomagnesemia paralyzes parathyroid PTH secretion AND target tissue PTH response → functional hypocalcemia that won't correct on calcium alone. Replete Mg first; calcium follows. Often missed in ED.
→Bone
99% of your calcium lives in bone as hydroxyapatite crystals grown along collagen ropes. Let blood calcium dip and PTH sends osteoclasts to mine it back out — bone is calcium's current account, not its vault.
The moment an action potential arrives, the sarcoplasmic reticulum dumps its stored calcium into the cytosol; calcium clicks onto troponin, and only then does myosin's binding site come into view. No calcium, no cross-bridge.
Calcium is the building material, but absorption has a ceiling: past roughly 500 mg in one dose the fraction absorbed falls, so take it with meals and split it. Food first, supplements for the gap — a large single dose mostly just passes through the kidney.
Otoconia are calcium carbonate crystals. Being denser than the fluid around them, gravity pulls the gelatinous membrane they sit on, which drags the hair-cell bundles to one side — that is how the body knows its orientation to gravity.
antagonism · 3
↮Iron
Calcium competes with non-heme iron at the gut; high-calcium meals lower iron absorption.
High sodium → reduced distal-tubule Ca reabsorption → urinary Ca ↑. Each +2.3 g Na = +25 mg urinary Ca. Chronic high-Na + low Ca + low D = silent bone-loss trifecta.
↮Zinc
High calcium mildly reduces zinc absorption — usually trivial unless zinc is borderline.
depletes · 1
Caffeine does depress intestinal calcium absorption — but only very slightly, and it has no effect on total 24-hour urinary calcium (Heaney 2002). How slight? One to two tablespoons of milk fully offsets it. In people meeting their calcium RDA there is no evidence caffeine harms bone. The teaching value of this edge is precisely how small it is: a real interaction that marketing inflated into a big one.
regulates · 3
Calcitriol opens the active intestinal calcium channel. No D = no absorption.
K2 routes calcium: activates osteocalcin (into bone) and MGP (out of arteries).
Estrogen has been holding osteoclasts down the whole time. After menopause it falls by roughly 90%; with the brake released, the first years lose bone calcium faster than they lay it down — around 20% of density over 5-10 years.