Calcium citrate and blood calcium levels from different sources in women
What it found
A single 500 mg dose of calcium citrate raised blood calcium for up to 6 hours in ten older women.
Calcium from a dairy meal caused a smaller rise than the supplement or fortified juice.
What they found
Studies in people
Blood calcium after citrate
Taking 500 mg of calcium citrate while fasting raised both types of measured blood calcium over 6 hours. The levels stayed above the starting point throughout that time.
Dairy versus supplement
The dairy meal led to a smaller rise in blood calcium than taking calcium citrate while fasting. The authors suggest protein and fat in dairy might slow how fast calcium enters the blood.
Fortified juice matched citrate
Drinking juice fortified with 500 mg of calcium raised blood calcium by about the same amount as the calcium citrate taken while fasting.
Eating delayed the rise
Taking calcium citrate right after a meal delayed the rise in blood calcium by 1 to 2 hours. However, the overall increase was not reduced compared to taking it while fasting.
Phosphate levels varied
Blood phosphate dropped after taking calcium citrate while fasting and after drinking fortified juice. It rose after taking calcium citrate with a meal and after eating the dairy meal.
What the authors conclude
- They conclude that different sources of calcium have different short-term effects on blood calcium levels in people.
- Their results support recommendations that getting calcium from food might be better for the heart than taking supplements.
- They advise that more research is needed to find out whether these differences in blood calcium actually affect heart health.
How it was done
Past research linked calcium supplements, but not calcium from food, to a higher risk of heart problems. The authors wanted to see if different calcium sources change blood calcium levels in different ways.
Ten postmenopausal women with an average age of 69 years each took 500 mg of calcium on four separate days. They received it as calcium citrate while fasting, calcium citrate with a meal, fortified juice, or a dairy meal. Blood was tested before and for 6 hours after each dose, with at least 6 days between sessions.
What it can’t tell you
- This trial only included ten postmenopausal women, so the results might differ for men, younger people, or other ethnic groups.
- The study measured blood calcium over just 6 hours, so it cannot show what happens with long-term daily use.
- It does not measure heart problems directly, so it cannot prove that changes in blood calcium lead to heart risks.
Who paid
- Authors work at
- University of Auckland, New Zealand
The paper
- Title
- Acute effects of calcium citrate with or without a meal, calcium-fortified juice and a dairy product meal on serum calcium and phosphate: a randomised cross-over trial
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Bristow SM, Gamble GD, Stewart A, Kalluru R, Horne AM, Reid IR (2015). Acute effects of calcium citrate with or without a meal, calcium-fortified juice and a dairy product meal on serum calcium and phosphate: a randomised cross-over trial. The British journal of nutrition. doi:10.1017/S000711451500080XFree full textPubMed 25851635DOI
Summary written 1 Oct 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error