Calcium citrate and calcium carbonate absorption after gastric bypass surgery
What it found
In people who had gastric bypass surgery, calcium citrate raised blood calcium levels more than calcium carbonate.
It also lowered a hormone linked to bone loss more effectively.
What they found
Studies in people
Blood calcium levels
Peak blood calcium was higher after taking calcium citrate compared to calcium carbonate. The total amount of calcium measured in the blood over six hours was also greater with calcium citrate.
Parathyroid hormone levels
A hormone called PTH dropped much more after calcium citrate than after calcium carbonate. Twelve of the 18 patients had their lowest PTH level after taking calcium citrate.
Calcium in urine
Urine calcium rose significantly after taking calcium citrate but stayed about the same after calcium carbonate. The ratio of calcium to creatinine in urine also went up more with calcium citrate.
Other findings
Why citrate may work better
The authors note that calcium carbonate needs stomach acid to dissolve, while calcium citrate dissolves partly in water. Gastric bypass surgery reduces stomach acid, which may explain why calcium citrate was taken in better.
What the authors conclude
- They conclude that calcium citrate is taken in by the body better than calcium carbonate in people who have had gastric bypass surgery.
- They suggest calcium citrate may be better at lowering the hormone linked to bone loss after this operation.
- They call for longer studies using different supplement forms to confirm these results.
How it was done
After gastric bypass surgery, food skips the main part of the gut that takes in calcium. This can lead to bone loss and kidney stones, so the authors wanted to compare two common calcium supplements.
Eighteen adults who had gastric bypass surgery about a year earlier each took a single 500 mg dose of calcium citrate and calcium carbonate on separate test days. Blood and urine were collected over six hours after each dose to measure calcium and hormone levels.
What it can’t tell you
- This trial only looked at what happened over six hours after a single dose.
- It cannot show whether one supplement protects bones or prevents kidney stones over months or years.
- The study included mostly women, so the results might differ in men.
Who paid
- Funding
- Funded by NCRR NIH HHS (from the PubMed record).
- Authors work at
- Charles and Jane Pak Center for Mineral Metabolism, USA
The paper
- Title
- Comparison of the absorption of calcium carbonate and calcium citrate after Roux-en-Y gastric bypass
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Tondapu P, Provost D, Adams-Huet B, Sims T, Chang C, Sakhaee K (2009). Comparison of the absorption of calcium carbonate and calcium citrate after Roux-en-Y gastric bypass. Obesity surgery. doi:10.1007/s11695-009-9850-6Free full textPubMed 19437082DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error