Calcium citrate and other supplements affect blood calcium and bone turnover
What it found
In 100 postmenopausal women, calcium citrate and calcium carbonate raised blood calcium for up to 8 hours after each dose, and this rise was still there after 3 months.
Both also reduced markers of bone breakdown over 8 hours and after 3 months.
What they found
Studies in people
Blood calcium rise
The citrate and carbonate dose raised ionised and total calcium levels in the blood for up to 8 hours, and this effect was not reduced after 3 months.
MCH versus citrate-carbonate
MCH raised ionised calcium less than the citrate and carbonate dose, but it increased phosphate levels and the calcium-phosphate product.
Bone breakdown
Both the citrate-carbonate and MCH doses produced similar decreases in a marker of bone resorption (CTX) over 8 hours.
Bone turnover at 3 months
After 3 months, both the citrate-carbonate and MCH doses produced similar decreases in bone turnover markers (CTX and procollagen type-I N-terminal propeptide).
What the authors conclude
“These findings suggest that Ca preparations, in general, produce repeated sustained increases in serum Ca concentrations after ingestion of each dose and that Ca supplements with smaller effects on serum Ca concentrations may have equivalent efficacy in suppressing bone turnover.”
Also in their conclusions
- They suggest that calcium preparations in general produce repeated sustained increases in blood calcium after each dose is taken.
- They say that calcium supplements with smaller effects on blood calcium may work just as well at suppressing bone turnover.
How it was done
Calcium supplements are used for bone health, but they have been linked to higher cardiovascular risk, which may be related to their short-term effects on blood calcium levels. The authors wanted to see if a supplement called microcrystalline hydroxyapatite (MCH) affects blood calcium less than standard calcium supplements, and how it affects bone turnover.
They randomly assigned 100 women (average age 71) to take 1 g per day of calcium as citrate or carbonate, one of two MCH preparations, or a placebo. Blood was sampled for 8 hours after the first dose and again after 3 months of daily supplementation. Eight women taking the citrate dose repeated the 8-hour blood sampling at 3 months.
What it can’t tell you
- We summarised it from the abstract only.
- This trial measured blood calcium and bone turnover markers, not heart health or broken bones.
- It cannot show whether the short-term rise in blood calcium affects cardiovascular risk over time.
Who paid
- Authors work at
- University of Auckland, New Zealand
The paper
- Title
- Acute and 3-month effects of microcrystalline hydroxyapatite, calcium citrate and calcium carbonate on serum calcium and markers of bone turnover: a randomised controlled trial in postmenopausal women
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Bristow SM, Gamble GD, Stewart A, et al (2014). Acute and 3-month effects of microcrystalline hydroxyapatite, calcium citrate and calcium carbonate on serum calcium and markers of bone turnover: a randomised controlled trial in postmenopausal women. The British journal of nutrition. doi:10.1017/S0007114514002785PubMed 25274192DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error