Story
Calcium
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In one pass Whether you get enough calcium depends not only on how much you eat but on how much your body actually absorbs.
Educational content, not medical advice — consult a clinician.
Blood Ca drops Normal blood calcium is tightly held at 2.2–2.6 mmol/L (8.8–10.4 mg/dL) — an extremely narrow window.
Bone constantly remodels Bone is not stone, it is living tissue — the adult skeleton remodels ~ 10% every year, getting a whole new skeleton in 10 years.
Story path
Chapter 1
Food
Whether you get enough calcium depends not only on how much you eat but on how much your body actually absorbs. In some foods, calcium is locked up by compounds such as oxalate and phytate, which form insoluble salts in the gut that pass straight through — so the calcium printed on the package never reaches you.
So when choosing foods for calcium, look at bioavailability: calcium content times the absorption rate, which is the part that finally gets into your body. The best-known example is spinach: it has a fair amount of calcium, but oxalate locks most of it away, so only about 5% is absorbed — spinach for calcium is basically a myth. On the other hand, low-oxalate dark greens such as kale (see Kale) and Chinese broccoli are absorbed about as well as milk (see Milk), or slightly better.
If you do not drink milk, there are still reliable routes:
Lactose intolerance: yogurt and hard cheese are low in lactose and are the easiest dairy substitutes (see Yogurt · see Cheese)Milk allergy or a vegan diet: calcium-fortified plant milks, tofu set with calcium sulfate (see Soybeans & Tofu), and small fish eaten with their bones (see Sardines)
Severely low or high blood calcium can be life-threatening, but it is almost always caused by illness or medicines, not by what you eat; if you have a seizure or a clearly irregular heartbeat, seek medical care immediately.
So when choosing foods for calcium, look at bioavailability: calcium content times the absorption rate, which is the part that finally gets into your body. The best-known example is spinach: it has a fair amount of calcium, but oxalate locks most of it away, so only about 5% is absorbed — spinach for calcium is basically a myth. On the other hand, low-oxalate dark greens such as kale (see Kale) and Chinese broccoli are absorbed about as well as milk (see Milk), or slightly better.
If you do not drink milk, there are still reliable routes:
Lactose intolerance: yogurt and hard cheese are low in lactose and are the easiest dairy substitutes (see Yogurt · see Cheese)Milk allergy or a vegan diet: calcium-fortified plant milks, tofu set with calcium sulfate (see Soybeans & Tofu), and small fish eaten with their bones (see Sardines)
Severely low or high blood calcium can be life-threatening, but it is almost always caused by illness or medicines, not by what you eat; if you have a seizure or a clearly irregular heartbeat, seek medical care immediately.
Numbers · Label calcium and what the body absorbs
Line up common foods by calcium content, absorption rate and the amount that actually gets into the body, and the gap is obvious (calcium content per 100 g):| Food | Calcium | Absorption rate | Amount absorbed |
|---|---|---|---|
| Milk, yogurt (see Milk · see Yogurt) | ~120 mg | ~32% | ~38 mg |
| Hard cheese (Cheddar, see Cheese) | ~720 mg | ~32% | ~230 mg |
| Kale (see Kale) | ~150 mg | ~41% | ~61 mg |
| Spinach | ~99 mg | ~5% | ~5 mg (locked by oxalate) |
| Fortified soy milk | ~120 mg | ~25% | ~30 mg |
| Sardines (with bones, see Sardines) | ~380 mg | ~27% | ~100 mg |
| Tofu (set with calcium sulfate, see Soybeans & Tofu) | ~350 mg | ~31% | ~108 mg |
How to read the table: the absorption rates are approximate values measured with isotope tracers. The NIH Office of Dietary Supplements (NIH ODS) summarizes that dairy products and calcium-fortified foods are absorbed at about 30%, spinach at only about 5%, and low-oxalate vegetables such as kale, broccoli and cabbage about as well as milk. The kale row comes from Heaney 1990, an isotope study that measured about 41% for kale and about 32% for milk.
The spinach row makes the point: it has a fair amount of calcium, but only about 5% is absorbed, so almost none of it actually reaches the body.
Two compounds that lock calcium up:
Oxalate: in spinach, amaranth, beet greens and cocoa, it locks calcium up — which is why spinach for calcium is basically a mythPhytate: in raw beans and whole grains, it also lowers calcium absorption; soaking, sprouting and fermenting break down a good share of it
If you eat a varied diet, there is little to worry about: NIH ODS considers that with a mixed diet, these effects of oxalate and phytate probably matter little nutritionally.
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In practice · Choosing and dosing calcium supplements
Calcium forms in supplements:Calcium carbonate: 40% calcium, the highest, but it needs stomach acid to dissolve well, so take it with food. Cheap. Common in calcium tablets, and also the ingredient in antacids such as Tums (so those antacids double as calcium supplements)Calcium citrate: 21% calcium, and much less dependent on stomach acid, so it suits older people, people taking proton-pump inhibitors () to suppress stomach acid, and people with atrophic gastritis; it can be taken on an empty stomachCalcium lactate and calcium gluconate: 9–13% calcium, well absorbed, but you need many tablets to reach a useful doseMicrocrystalline hydroxyapatite calcium: contains calcium, phosphate and a little protein; marketed as closer to bone, but the clinical evidence is weak, and it usually costs more
Dose rules:
No more than 500 mg at a time: the active absorption route has a ceiling, and the more you take at once, the smaller the share absorbed (NIH ODS)Keep the daily total (food plus supplements) within the tolerable upper intake level (): 2500 mg under age 50, 2000 mg over 50Food first: calcium from food does not carry the cardiovascular controversy that supplements do
Do calcium supplements raise cardiovascular risk? Bolland 2010 (BMJ) pooled randomized placebo-controlled trials of calcium supplements taken without vitamin D (≥ 500 mg/day) and found a relative increase of about 27% in the risk of heart attack in the calcium groups, which caused considerable controversy (heart attack was a secondary outcome in these trials, collected from self-reports and hospital records). In 2016, a guideline from the US National Osteoporosis Foundation and the American Society for Preventive Cardiology (Kopecky and colleagues, Ann Intern Med) concluded, on moderate-quality evidence, that calcium from food and supplements within the UL (2000–2500 mg/day) can be considered safe from a cardiovascular standpoint. NIH ODS's judgment is that the findings are inconsistent and more research is needed. So food first remains a sensible general rule.
Taking calcium together with vitamin D has better evidence for preventing fractures than calcium alone: a from the US National Osteoporosis Foundation (Weaver 2016), which pooled randomized trials including the large WHI trial, found that calcium plus vitamin D lowered the risk of any fracture by about 15% and of hip fracture by about 30%. For how much vitamin D to take, see the vitamin D story.
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Chapter 2
Two ways calcium gets absorbed
Calcium gets into the blood by two routes: one needs vitamin D to open the door, the other does not.
The active route (straight through the gut cells) works in the duodenum and upper jejunum, with three proteins passing calcium along:
1. A calcium channel (TRPV6) on the gut-facing membrane lets calcium into the cell
2. A calcium-binding protein (calbindin-D9k) inside the cell carries it across
3. A calcium pump (PMCA1b) on the blood-facing membrane pushes it into the bloodstream
All three take their orders from active vitamin D (1,25(OH)₂D) and its receptor, : without enough active D, this route opens only a crack.
The passive route (seeping through the gaps between cells) works in the lower jejunum and ileum, driven by the concentration difference and not controlled by vitamin D; the more you eat, the more you rely on it.
So the more you eat, the smaller the share you absorb. According to NIH ODS, about 36% of a single 300 mg dose of calcium is absorbed, but only about 28% of a 1000 mg dose. That is why one big 1000 mg tablet works less well than 500 mg at each of two meals.
The active route (straight through the gut cells) works in the duodenum and upper jejunum, with three proteins passing calcium along:
1. A calcium channel (TRPV6) on the gut-facing membrane lets calcium into the cell
2. A calcium-binding protein (calbindin-D9k) inside the cell carries it across
3. A calcium pump (PMCA1b) on the blood-facing membrane pushes it into the bloodstream
All three take their orders from active vitamin D (1,25(OH)₂D) and its receptor, : without enough active D, this route opens only a crack.
The passive route (seeping through the gaps between cells) works in the lower jejunum and ileum, driven by the concentration difference and not controlled by vitamin D; the more you eat, the more you rely on it.
So the more you eat, the smaller the share you absorb. According to NIH ODS, about 36% of a single 300 mg dose of calcium is absorbed, but only about 28% of a 1000 mg dose. That is why one big 1000 mg tablet works less well than 500 mg at each of two meals.
Mechanism · What helps calcium absorption, what blocks it
How much you eat versus how much you absorb: according to the NIH Office of Dietary Supplements (NIH ODS), when you eat 200 mg of calcium a day from food, about 45% is absorbed; above 2000 mg, only about 15%. Adults absorb about 25% on average, and less with age.What helps calcium absorption:
Vitamin D (the active form, 1,25(OH)₂D): it opens the active route and is the main switch for calcium absorption. Without enough active D, the active route opens only a crack and absorption has to rely on passive seepage; NIH ODS notes that low vitamin D status reduces net calcium absorption far more than caffeine or phosphorus doLactose (in milk): may help calcium seep between cells; this is fairly clear in infants, but the effect in adults is inconsistentAn acidic environment (stomach acid, vitamin C, citrate): dissolves less soluble forms such as calcium carbonate and calcium phosphate into absorbable calcium ionsEnough protein: a common claim is that high protein raises urinary calcium and so steals calcium from bone. In a randomized trial by Cao 2014 (39 young adults over 31 days, 21 of them eating 40% fewer calories than they needed), protein at 0.8, 1.6 or 2.4 g per kg of body weight a day made no difference to the calcium lost in urine or the calcium the body kept, and bone turnover markers were the same. A moderate amount of protein actually benefits bone, partly by raising insulin-like growth factor 1 (, a growth signal that promotes bone formation)
What blocks calcium absorption:
Oxalate: in spinach (about 5% absorbed), amaranth, beet greens, cocoa, almonds and sweet potatoes, it binds calcium into insoluble calcium oxalate that passes straight out. Spinach for calcium is the classic example of nutrition misinformationPhytate: in raw beans, nuts and whole grains. Soaking, sprouting and fermenting (leavened bread, sourdough) break down a good share of itVery high fiber intake (> 50 g/day): shortens the time food spends in the gut, a weak effectCaffeine: its effect is very small. Each 100 mg of caffeine reduces calcium absorption by roughly 6 mg, which 1–2 tablespoons of milk make up for, and it has no effect on 24-hour urinary calcium. The observations linking caffeine to osteoporosis all come from populations that were already eating too little calcium (Heaney 2002)Heavy drinking over the long term: suppresses bone-building cells and interferes with vitamin D metabolism
The other end: calcium lost in the urine. The more sodium you eat, the more calcium ends up in your urine, because the kidneys carry calcium out along with the sodium. This does not affect absorption; it affects excretion.
Two that are often overrated: eating a lot of phosphorus and eating a lot of protein. On current research, their effects on calcium balance are limited, and the old concerns have been overturned.
Three things that are often overlooked: a high-sodium diet over the long term, long-term low vitamin D, and long-term use of proton-pump inhibitors () to suppress stomach acid (calcium carbonate needs acid to dissolve well). Stacked together, they deserve to be looked at alongside the question of whether you eat enough calcium.
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Chapter 3
How blood calcium stays steady
Blood calcium cannot run too low or too high: too low brings spasms in the hands and feet and muscle cramps; too high brings abnormal heart rhythms and kidney stones. So the body holds it within a narrow band, adjusting it minute by minute.
The main players are parathyroid hormone () and vitamin D. As soon as blood calcium drops, the parathyroid glands in the neck release PTH, which acts on three fronts at once: it lets bone release a little calcium, makes the kidneys reclaim calcium that would otherwise be lost and, along the way, activates vitamin D, which in turn makes the small intestine absorb a bit more. When blood calcium is high, less PTH is released; calcitonin, made by the C cells of the thyroid, also applies a light brake, but it plays only a small role in adults.
The key point: one normal blood calcium result says nothing about whether you eat enough calcium; it only shows that the control system is still working. When calcium intake stays low for a long time, the body quietly borrows calcium from bone to keep blood levels steady: blood calcium stays normal while bone slowly empties. So judging calcium status means looking at () together with 24-hour urine calcium, and PTH, not at blood calcium alone.
The main players are parathyroid hormone () and vitamin D. As soon as blood calcium drops, the parathyroid glands in the neck release PTH, which acts on three fronts at once: it lets bone release a little calcium, makes the kidneys reclaim calcium that would otherwise be lost and, along the way, activates vitamin D, which in turn makes the small intestine absorb a bit more. When blood calcium is high, less PTH is released; calcitonin, made by the C cells of the thyroid, also applies a light brake, but it plays only a small role in adults.
The key point: one normal blood calcium result says nothing about whether you eat enough calcium; it only shows that the control system is still working. When calcium intake stays low for a long time, the body quietly borrows calcium from bone to keep blood levels steady: blood calcium stays normal while bone slowly empties. So judging calcium status means looking at () together with 24-hour urine calcium, and PTH, not at blood calcium alone.
Mechanism · How PTH pulls blood calcium back
Normal blood calcium: ~2.2–2.6 mmol/L, 8.8–10.4 mg/dL. Large departures cause symptoms: too low brings spasms of the hands and feet and muscle cramps; too high brings abnormal heart rhythms and kidney stones. Mild departures that develop slowly often cause no symptoms at all.When blood calcium drops:
1. The parathyroid glands immediately release (parathyroid hormone)
2. In bone, PTH activates osteoclasts (the cells that break bone down) through a signal called , releasing calcium into the blood
3. In the kidneys, PTH increases calcium reabsorption, raises CYP27B1 (the enzyme that turns vitamin D into its active form) and reduces phosphate reabsorption
4. Active vitamin D (1,25(OH)₂D) acts on the small intestine to increase calcium absorption, and blood calcium recovers
When blood calcium rises:
1. PTH release falls, and all of the effects above are dialed back
2. The C cells of the thyroid release calcitonin, which restrains osteoclasts and reduces reabsorption in the kidneys, so blood calcium falls; but in adults calcitonin plays only a small role — blood calcium stays steady even after the thyroid is removed
There is also FGF23 (fibroblast growth factor 23), a hormone made by bone cells that mainly controls phosphate: it makes the kidneys excrete more phosphate and also holds down the production of active vitamin D, affecting calcium indirectly.
Clinical · How hyperparathyroidism quietly takes bone
Primary hyperparathyroidism (1° HPT): one or more parathyroid glands produce too much on their own and no longer respond to feedback from blood calcium.Who gets it: it is not rare; it is more common in women than in men and peaks in women after menopause. Most people have no symptoms and are found by chance on a routine test that shows slightly high blood calcium together with PTH that should be suppressed but is high instead.
Consequences:
With PTH persistently high, osteoclasts keep dissolving bone, so blood calcium creeps up and fallsThe kidneys have to handle a large calcium load, so kidney stones (calcium oxalate, calcium phosphate) form more easilyHigh blood calcium dampens the nervous system: fatigue, low mood, poor memory. The classic memory aid is Bones, stones, groans, psychic moans (bone pain, kidney stones, gut complaints, low mood)
The typical lab picture: persistently high blood calcium, high PTH and adequate vitamin D. Two things need to be ruled out first: secondary hyperparathyroidism caused by vitamin D deficiency, and a harmless inherited condition, familial hypocalciuric hypercalcemia (FHH), which is told apart by low urine calcium. Once the diagnosis is confirmed, surgical removal of the adenoma usually resolves it completely.
Why this matters: it shows that normal or slightly high blood calcium in no way means enough calcium — the skeleton may be quietly emptying. Anyone with a sudden fall in bone density, recurrent kidney stones and unexplained fatigue together should ask a doctor to measure PTH, blood calcium, and 24-hour urine calcium and interpret them together.
Chapter 4
How bone stores and releases calcium
99% of the body's calcium lives in bone, mostly as crystals of hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, bound to a scaffold of collagen. But bone is not a stone: it is constantly being broken down and rebuilt:
Osteoblasts lay down new matrix on the bone surface and then mineralize itOsteoclasts use acid and enzymes to dissolve bone, returning calcium, phosphate and fragments of collagen to the bloodOsteocytes, embedded in the bone matrix, sense mechanical load and direct the other two through a set of signals called / RANK / OPG
In adults, about 10% of the skeleton is renewed each year — roughly a new skeleton every ten years. Which side wins, breakdown or building, changes over a lifetime: building dominates in youth, the two balance in midlife, and breakdown gains the upper hand with age.
The most important window is ages 0–30: calcium, protein, vitamin D and exercise (especially weight-bearing exercise and jumping) in childhood, adolescence and young adulthood determine peak bone mass, one of the biggest factors in fracture risk after 50. Bank too little before 30, and there is less to spend after 60.
Osteoblasts lay down new matrix on the bone surface and then mineralize itOsteoclasts use acid and enzymes to dissolve bone, returning calcium, phosphate and fragments of collagen to the bloodOsteocytes, embedded in the bone matrix, sense mechanical load and direct the other two through a set of signals called / RANK / OPG
In adults, about 10% of the skeleton is renewed each year — roughly a new skeleton every ten years. Which side wins, breakdown or building, changes over a lifetime: building dominates in youth, the two balance in midlife, and breakdown gains the upper hand with age.
The most important window is ages 0–30: calcium, protein, vitamin D and exercise (especially weight-bearing exercise and jumping) in childhood, adolescence and young adulthood determine peak bone mass, one of the biggest factors in fracture risk after 50. Bank too little before 30, and there is less to spend after 60.
Numbers · When bone is banked, and when it is spent
Bone mass is not a flat line. It has a saving period, a plateau and a withdrawal period:Ages 0–18: bone building far outpaces breakdown, and bone mass growsAges 18–30: peak bone mass is reached — the baseline for lifeAges 30–50: a plateauAfter 50: breakdown outpaces building, and bone mass falls by 0.5–1% a year; in the first 5 years after menopause, women's loss speeds up to 1–2% a year
So peak bone mass sets how high the starting point is, and the rate in the second half of life sets how fast it falls. Both ends can be influenced, but the windows are different.
Clinical · How to read a bone density report
Dual-energy X-ray absorptiometry (, also written DEXA) is the standard way to measure . It measures bone mineral content per square centimeter (g/cm²) at the lumbar spine and hip (sometimes also the radius in the forearm).Two key numbers:
T-score: how many standard deviations your bone density is above or below that of a healthy young adult (about 30 years old)≥ -1.0: normal-1.0 to -2.5: low bone mass (osteopenia) — a warning, not a disease≤ -2.5: osteoporosis — the diagnosis is established≤ -2.5 with a previous fragility fracture: severe osteoporosisZ-score: a comparison with people of the same age and sex, used for younger people to see whether you are worse than your peers
Screening recommendations:
Women aged 65 and over (US Preventive Services Task Force, USPSTF), or earlier after menopause for women with risk factors (family history, early menopause, long-term glucocorticoid use, smoking, low body mass index)Men aged 70 and over (recommended by NOF and ISCD; for screening men, the USPSTF gives an I statement, meaning the evidence is insufficient to weigh benefits and harms), or earlier for men with risk factorsA previous fragility fracture (a break from a fall from standing height): get tested soon
How to read a T-score: the lower the T-score, the higher the fracture risk; the link is strongest when hip bone density is used to predict hip fracture, where each standard deviation lower raises the risk about 2–3 times. But low bone mass (-1 to -2.5) does not mean a fracture is coming: most people with low bone mass never break a bone in their lifetime. The FRAX tool combines age, T-score and risk factors into a 10-year fracture probability, which is a more practical guide (for how FRAX is used and whether to take medication, see the osteoporosis story).
An unchanged T-score does not mean treatment has failed: bone quality (microstructure, collagen cross-links) may improve before density does, and the benefit of fewer falls does not show up in density at all.
Chapter 5
Muscle & nerve
Every muscle contraction and relaxation is calcium moving in and out inside the cell.
Contraction: when an electrical signal arrives, the muscle cell's calcium store (the sarcoplasmic reticulum, SR) opens its gates and calcium floods into the cell fluid. Calcium binds troponin C, which uncovers the binding sites on actin; myosin grabs on and pulls, and the muscle shortens.
Relaxation: the calcium has to be pumped back into the store. That job belongs to the SERCA calcium pump, which uses 1 magnesium-bound (ATP-Mg²⁺) for every 2 Ca²⁺ it pumps back into the sarcoplasmic reticulum.
Common cramps, muscle twitches, eyelid twitches and teeth grinding cannot simply be read as calcium deficiency — nor as magnesium deficiency: people who are truly short of magnesium do get cramps, but only once the deficiency has become fairly severe; the Cochrane review by Garrison 2020, which pooled cramp trials mostly in older adults, found that magnesium is unlikely to give clinically meaningful protection. What is truly dangerous is severely low or high blood calcium: when it is severely low, numbness around the mouth and in the hands and feet and muscle spasms are common, and in serious cases there can be seizures or abnormal heart rhythms; if these appear, seek medical care immediately.
Contraction: when an electrical signal arrives, the muscle cell's calcium store (the sarcoplasmic reticulum, SR) opens its gates and calcium floods into the cell fluid. Calcium binds troponin C, which uncovers the binding sites on actin; myosin grabs on and pulls, and the muscle shortens.
Relaxation: the calcium has to be pumped back into the store. That job belongs to the SERCA calcium pump, which uses 1 magnesium-bound (ATP-Mg²⁺) for every 2 Ca²⁺ it pumps back into the sarcoplasmic reticulum.
Common cramps, muscle twitches, eyelid twitches and teeth grinding cannot simply be read as calcium deficiency — nor as magnesium deficiency: people who are truly short of magnesium do get cramps, but only once the deficiency has become fairly severe; the Cochrane review by Garrison 2020, which pooled cramp trials mostly in older adults, found that magnesium is unlikely to give clinically meaningful protection. What is truly dangerous is severely low or high blood calcium: when it is severely low, numbness around the mouth and in the hands and feet and muscle spasms are common, and in serious cases there can be seizures or abnormal heart rhythms; if these appear, seek medical care immediately.
Mechanism · Six calcium steps in one contraction
Contraction (when the action potential arrives):1. L-type calcium channels (on the T-tubule membrane) sense the change in voltage and send the trigger
2. Ryanodine receptors (RyR) on the sarcoplasmic reticulum (SR) open and release stored Ca²⁺, and the calcium concentration in the cell fluid jumps about 100-fold
3. Ca²⁺ binds troponin C, uncovering the sites on actin where myosin binds; the cross-bridge cycle starts and the muscle contracts
Relaxation:
4. The SERCA calcium pump (on the SR membrane) pumps Ca²⁺ back into the SR for storage
5. PMCA and NCX (a calcium pump and a sodium-calcium exchanger in the cell membrane) move excess calcium out of the cell
6. Calcium in the cell fluid falls, troponin lets go, the cross-bridges detach, and the muscle relaxes
Safety · Why calcium imbalance endangers the heart
Heart muscle also relies on the sarcoplasmic reticulum to release calcium for contraction, but the trigger differs from skeletal muscle: with each heartbeat, a small amount of calcium first flows in from outside the cell through L-type calcium channels, and that small influx then triggers a large release of calcium from the SR (calcium-induced calcium release). So heart muscle depends more on calcium outside the cell than skeletal muscle does, and large departures in blood calcium affect both the heart's electrical activity and its contraction.How abnormal blood calcium shows on an ECG:
Low calcium (< 2.0 mmol/L): QT prolongation (slower recovery of the ventricles between beats), which raises the risk of torsades de pointesHigh calcium (> 3.0 mmol/L): QT shortening, sometimes with a prominent J wave, and a risk of ventricular fibrillation, with cardiac arrest in severe cases
Dangerous electrolyte combinations:
Low potassium, low magnesium and low calcium together: the risks of arrhythmia add up; seen in chronic diarrhea, diuretic misuse, eating disorders and long-term heavy drinkingPeople taking digoxin: low potassium makes it easier for digoxin to bind its target, the Na⁺/K⁺-ATPase, while high calcium raises the calcium inside heart cells, adding to digoxin's effect. Both make arrhythmias from digoxin toxicity more likely
Calcium protects the heart is far too simple:
Calcium from food: observational studies show no consistent link with cardiovascular diseaseCalcium supplements without vitamin D: in the Bolland 2010 they were linked to a higher risk of heart attack; the 2016 guideline from two US societies concluded that intake within the can be considered safe from a cardiovascular standpoint; the NIH Office of Dietary Supplements judges the findings inconsistent. One proposed mechanism is the brief spike in blood calcium after a large single dose, but this is still speculationThe steadier approach: get enough calcium from food while making sure of vitamin D, potassium and magnesium; eating patterns such as DASH are themselves rich in potassium, magnesium and calcium
So if the heart rhythm suddenly becomes unstable — especially in someone who has been eating very little for a long time, is taking diuretics or has been vomiting repeatedly — seek medical care immediately; the first step is usually a full electrolyte panel (potassium, magnesium, calcium and phosphate), not just an ECG.
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References · 5
- National Institutes of Health, Office of Dietary Supplements. (2024). Calcium — Fact Sheet for Health Professionals. ods.od.nih.gov/factsheets/Calcium-HealthProfessional
- Heaney, R. P. (2002). Effects of caffeine on bone and the calcium economy. Food and Chemical Toxicology, 40(9), 1263–1270. Review: caffeine has a clear but very small depressant effect on intestinal calcium absorption and no effect on total 24-h urinary calcium excretion; the effect is fully offset by 1-2 tablespoons of milk; observational links may reflect lower milk intake; no evidence of harm to bone in people who meet recommended calcium intakes (abstract, PMID 12204390). 10.1016/S0278-6915(02)00094-7
- Weaver, C. M., et al. (2016). Calcium plus vitamin D supplementation and risk of fractures: an updated meta-analysis from the National Osteoporosis Foundation. Osteoporosis International, 27(1), 367–376. 10.1007/s00198-015-3386-5
- Institute of Medicine. (2011). Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press. www.ncbi.nlm.nih.gov/books/NBK56070
- Garrison, S. R., Korownyk, C. S., Kolber, M. R., Allan, G. M., Musini, V. M., Sekhon, R. K., & Dugré, N. (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, 2020(9), CD009402. 10.1002/14651858.CD009402.pub3