Calcium

Major mineral · bones & signals

What does Calcium do in your body?

About 99% of your calcium is in bones and teeth. The other 1% triggers muscle contraction, nerve signals and blood clotting.

How it works, step by step

  1. Vitamin D (as calcitriol) switches on calcium transporters in the gut.
  2. Calcium enters the blood; levels are held in a narrow range.
  3. Parathyroid hormone pulls calcium from bone when blood levels dip.
  4. Bone is constantly rebuilt, depositing calcium into new mineral.

What does Calcium do?

Builds bone mineral (hydroxyapatite). Inside cells, a burst of calcium is the switch for muscle contraction, hormone release and nerve-signal transmission.

Where does Calcium act in the body?

Bones and teeth, muscle fibers, nerves, blood (clotting).

Which foods contain Calcium?

Milk, yogurt, cheese, calcium-set tofu, fortified plant drinks, canned fish with bones, kale, bok choy, almonds.

How much Calcium do adults need?

RDA: 1,000 mg (ages 19–50; men to 70); 1,200 mg (women 51+, men 71+). Upper limit: 2,500 mg (19–50), 2,000 mg (51+).

What happens with too little Calcium?

Blood calcium is tightly controlled, so low intake shows up slowly — the body draws calcium from bone, which over years can contribute to osteoporosis.

Can you get too much Calcium?

Mostly from supplements: constipation, and higher kidney stone risk in some people. Very high blood calcium is a medical problem with other causes.

What does Calcium interact with?

Vitamin D is needed to absorb it well. Large calcium doses can reduce iron and zinc absorption if taken together.

What is known and unknown about Calcium?

Role in bone is established. Whether supplements (vs. food) affect heart risk is debated.

Evidence & sources

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.