Calcium carbonate and citrate effects on blood calcium and bone turnover
What it found
In postmenopausal women, calcium carbonate and calcium citrate raised blood calcium levels for 8 hours after a dose.
Both forms slowed bone breakdown just as much as each other over 3 months.
What they found
Studies in people
Blood calcium rise
Both calcium citrate and calcium carbonate raised blood calcium levels for up to 8 hours after a single 1 g dose. This rise was still present after 3 months of daily use.
Citrate versus carbonate
There were no differences between the calcium citrate and calcium carbonate groups. They raised blood calcium by the same amount and lowered bone turnover markers equally.
Bone turnover markers
After 3 months, both calcium citrate and calcium carbonate lowered two markers that show how fast bone is breaking down and being rebuilt. The drop was about the same for both forms.
Parathyroid hormone levels
Taking either calcium citrate or calcium carbonate caused a drop in parathyroid hormone over 8 hours. After 3 months, this hormone level remained slightly lower than in the group taking the dummy pill.
What the authors conclude
- They conclude that calcium citrate and calcium carbonate produce sustained rises in blood calcium after each dose.
- They note that both conventional calcium forms worked equally well at slowing bone turnover over 3 months.
- They suggest getting calcium from food remains the best approach, and call for more research into supplement forms that release calcium slowly.
How it was done
Calcium supplements are widely used for bone health but have been linked to heart problems in some studies. The authors wanted to see how different calcium forms affect blood calcium levels and bone turnover markers.
The researchers assigned 100 postmenopausal women, with an average age of 71 years, to take 1 g per day of calcium as citrate, carbonate, or another form, or a dummy pill. They took blood samples for 8 hours after the first dose and again after 3 months of daily use.
What it can’t tell you
- This trial lasted only 3 months, so it cannot show what happens to bones or hearts over many years of supplement use.
- It measured blood markers rather than actual broken bones or heart events, so it cannot directly show whether these supplements prevent fractures or cause heart problems.
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
- Full text
- 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/S0007114514002785Free full textPubMed 25274192DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error