Compound or practice · Supplement
Calcium
Food-first for bone; the supplement matters mainly when dairy is out — and megadosing may not be free of cardiovascular cost.
- Overall grade
- Grade B
- Last revised
- 2
- graded outcomes
- 0
- references listed
A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.
1 at grade B · 1 at grade C — 2 graded rows
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Fracture risk (with D, deficient)Evidence grade B
In the under-supplied
Smallmixed
- Cardiovascular risk (supplements)Evidence grade C
Debated small increase
Smallmixed
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Thin evidence: Cardiovascular risk (supplements) (grade C).
- Studies disagree: Fracture risk (with D, deficient) (mixed agreement).
- Watch with Iron: Blunts iron absorption — separate.
Interactions
Documented pairings with supplements and medicines. A medicine on this list is a conversation for whoever prescribes it.
IronMind the timing
Blunts iron absorption — separate.
LevothyroxineMind the timing
Binds thyroid hormone — separate by 4 hours.
Vitamin DWorks together
D drives calcium absorption.
Vitamin K2Works together
K2 directs calcium to bone, not arteries.
The evidence in words
What it is
Calcium is the most abundant mineral in the body, almost all of it in bone, with a small tightly-regulated pool doing signaling work. Requirements are usually met by dairy; supplements fill the gap for those who avoid it.
How it works
Beyond bone matrix, calcium ions trigger muscle contraction, nerve transmission, and clotting. Vitamin D governs its absorption and vitamin K2 governs where deposited calcium ends up.
What the evidence shows
Adequate calcium plus vitamin D reduces fracture risk in deficient and older populations — grade B, benefit concentrated in the under-supplied. The wrinkle is a debated signal that calcium supplements (less so dietary calcium) may modestly raise cardiovascular risk, which is one reason food sources and K2 co-supplementation are preferred over large isolated calcium pills.
How to use it
Aim for ~1,000–1,200 mg/day total from all sources; supplement only the shortfall, in doses ≤500 mg at a time (absorption saturates). Citrate absorbs without stomach acid; carbonate needs food.
Safety & interactions
Constipation and, at high supplemental doses, kidney-stone and possibly cardiovascular concerns. Prefer dietary calcium and modest supplemental top-ups with D and K2. Vitamin D — D drives calcium absorption. Vitamin K2 — K2 directs calcium to bone, not arteries. Iron — Blunts iron absorption — separate. levothyroxine — Binds thyroid hormone — separate by 4 hours.
Bottom line
Cover calcium from food if you can. If you supplement, keep single doses small, pair with vitamin D and K2, and don't chase megadoses — bigger is not safer here.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Top-up
- ≤500 mg per dose, with D and K2; citrate needs no acid.
Goes with
- Vitamin DD drives calcium absorption.Evidence grade A
- Vitamin K2K2 directs calcium to bone, not arteries.Evidence grade B
Related reading
Entries that share this one's tags or conditions.
- Calcium for Cardiovascular risk (supplements)Evidence grade C — Debated small increaseEvidence grade C
- Calcium for Fracture risk (with D, deficient)Evidence grade B — In the under-suppliedEvidence grade B
- Calcium: dosage and how to take it≤500 mg per dose, with D and K2; citrate needs no acid.Evidence grade B
- Calcium: side effects, safety & interactionsConstipation and, at high supplemental doses, kidney-stone and possibly cardiovascular concerns. Prefer dietary calcium Evidence grade B
Sources
This entry lists no references of its own.
Last revised . A grade is this entry's reading of the evidence, not medical advice.