Calcium citrate and calcium carbonate absorption after weight loss surgery in people
What it found
In people who had weight loss surgery, calcium citrate was absorbed slightly better than calcium carbonate over 8 hours.
Calcium citrate also lowered a hormone linked to bone loss more than calcium carbonate did.
What they found
Studies in people
Blood calcium levels
Peak blood calcium was 9.8 mg/dL after taking calcium citrate and 9.5 mg/dL after calcium carbonate. Total calcium taken in over 8 hours was also slightly higher with citrate at 76.1 mg/dL·h compared to 74.7 mg/dL·h for carbonate.
Parathyroid hormone levels
A hormone that rises when calcium is low dropped more after calcium citrate than after calcium carbonate. This drop happened between 3 and 6 hours after taking the supplement.
Calcium in urine
Over 9 hours, people passed 83.7 mg/dL of calcium in their urine after taking citrate. That was more than the 68.6 mg/dL passed after taking carbonate, suggesting the body took in more from the citrate form.
Differences by surgery type
People who had sleeve gastrectomy surgery took in more calcium than those who had bypass surgeries. There was no clear difference between the two types of bypass surgery.
What the authors conclude
- They found that calcium citrate was taken in slightly better than calcium carbonate and lowered parathyroid hormone levels more effectively after weight loss surgery.
- They note that while the differences were statistically clear, they were small in size.
- They advise that more research is needed to see if these small differences actually matter for long-term bone health.
How it was done
Weight loss surgeries change the gut and can make it harder for the body to take in calcium, which is needed for strong bones. The authors wanted to find out which form of calcium supplement works best after three common types of these surgeries.
The researchers studied 150 adults about 10 months after having one of three types of weight loss surgery. Each person took both calcium citrate and calcium carbonate on separate days, with blood and urine tests over 8 to 9 hours each time.
What it can’t tell you
- This trial only followed people for 8 to 9 hours on each test day. It cannot show whether one form of calcium protects bones better than the other over months or years.
- Almost all participants were women, so the results might not apply equally to men.
- The study did not measure bone strength directly, so it cannot show how these supplements affect actual bone health.
Who paid
- Authors work at
- Alexandria University, Egypt; Bariatric Surgery at Madina Women's Hospital, Egypt; Vrije Universiteit Brussel, Belgium
The paper
- Title
- Comparison of calcium citrate and calcium carbonate absorption in patients with a Roux-en-Y gastric bypass, sleeve gastrectomy, and one-anastomosis gastric bypass: a double-blind, randomized cross-over trial
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Hany M, Wuyts S, Abouelnasr AA, et al (2025). Comparison of calcium citrate and calcium carbonate absorption in patients with a Roux-en-Y gastric bypass, sleeve gastrectomy, and one-anastomosis gastric bypass: a double-blind, randomized cross-over trial. Surgery for obesity and related diseases. doi:10.1016/j.soard.2024.10.034Free full textPubMed 39603923DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error