Do calcium supplements harm your heart?

Probably a little, if you are a healthy postmenopausal woman taking a large supplement you do not need, and the effect is small enough that two careful meta-analyses of the same trials reached opposite conclusions. Calcium from food carries no such signal at all. That difference between the tablet and the plate is the most useful thing on this page.

Established. Calcium itself is not in question. It builds bone, and a small pool of it in the blood runs muscle contraction, nerve signalling and blood clotting. The argument is narrower: whether swallowing 1,000 mg of it at once, as a tablet, does something to arteries that the same amount spread through meals does not.

Why the answer keeps changing

No trial has ever been designed to test this. Every number below comes from trials built to study bone, with heart attacks counted along the way, or from cohorts that followed people who chose their own supplements. That is why competent researchers reading the same evidence come out in different places.

The case that supplements raise risk

Pooling 13 double-blind placebo-controlled trials in more than 43,000 people, calcium supplements were associated with 15 per cent more cardiovascular disease and 16 per cent more coronary heart disease, with no disagreement between the trials at all. The signal was specific to healthy postmenopausal women, which is who most of these trials enrolled.

The Women's Health Initiative then followed 36,282 women for 22 years after a seven-year trial of calcium with vitamin D. Cardiovascular deaths came out 6 per cent higher. Cancer deaths came out 7 per cent lower. Deaths from all causes came out exactly level.

Unsettled. Those two results pull against each other inside the same trial, and the authors say plainly that they cannot separate what the calcium did from what the vitamin D did. A finding that moves two causes of death in opposite directions and leaves total deaths unchanged is a finding to hold loosely.

The case that it does not

A second meta-analysis, published in 2023 and covering 12 randomised trials, found no association between calcium supplements and heart attacks, strokes, heart failure admissions or death from any cause. Subgroup analyses by sex, by follow-up length, by region and by whether vitamin D was given alongside did not change that.

The two reviews overlap heavily in the trials they include. They differ in which trials they allowed in, how they handled trials that reported cardiovascular events as adverse events rather than as outcomes, and which statistical model they used. There is no hidden trick in either one. This is what a genuinely borderline effect looks like when two teams process it.

An expert panel that reviewed the same field concluded on moderate-quality evidence that calcium from food or supplements neither increases nor decreases cardiovascular risk. That sentence is worth reading as an admission of uncertainty rather than as a clean bill of health.

What food says

The observational evidence runs the other way, and it is worth knowing why that is not a contradiction. Across 35 prospective cohorts with 163,657 deaths, higher total calcium intake tracked with slightly lower cardiovascular mortality and dietary calcium tracked with slightly lower deaths overall. Supplemental calcium tracked with nothing.

Myth. Those cohort numbers do not mean milk protects your heart. People who eat more calcium from food eat differently in a dozen other ways, and cohorts cannot untangle that. What the cohorts do establish is the absence of a harm signal from food, which matters because it is the supplement, not the mineral, that the trials flagged.

Food is not automatically the comfortable side of this argument either. Two Swedish cohorts followed 61,433 women for twenty years and 45,339 men for eleven. Every extra glass of milk a day went with a slightly higher fracture risk in women rather than a lower one: a hazard ratio of 1.02 for any fracture and 1.09 for the hip. In men the same estimates sat on no effect. A glass there means a measured 200 mL, which is worth knowing before applying anything about three glasses a day to your own mug. The authors ask for caution themselves, because people warned about their bones drink more milk. And no randomised trial of milk drinking against fractures or death has ever been run, so both the reassuring and the alarming readings of milk rest on people who chose what to drink.

There is a plausible mechanism for that difference, and it is the one line of biology worth carrying away. Calcium from a tablet arrives all at once and pushes blood calcium up for hours. Calcium in food arrives with everything else and barely moves it. Absorption fits the same picture: about 36 per cent of a 300 mg dose is absorbed against 28 per cent of a 1,000 mg dose, which is why supplements are recommended in doses of 500 mg or less.

What you actually give up by stopping

This is where most articles about calcium and the heart go quiet, and it is the part that decides what to do.

The thing calcium is for is bone, and the cost of getting too little is not hypothetical. Long-term shortage reduces bone strength and leads to osteoporosis, and in more severe cases to osteomalacia, where bone fails to mineralise and softens. Blood calcium stays normal the whole time, because the body takes what it needs from the skeleton, so nothing warns you.

In the Cochrane review of 9 trials in 49,853 people, vitamin D taken with calcium reduced hip fractures by 16 per cent. In absolute terms that is about one fracture prevented per 1,000 people a year among those living at home, and about nine per 1,000 a year among those living in care homes, because they break far more hips to begin with. The same combination carried a 16 per cent increase in kidney disease and more than double the rate of mild high blood calcium, and did not change death rates either way.

And the bone case has weakened since

The largest review of that question now runs to 69 trials and 153,902 people, and it found little to no effect of calcium supplements on breaking a bone. Calcium alone came out at a risk ratio of 0.91, from 0.81 to 1.01, at moderate certainty. Vitamin D alone came out at exactly 1.00 with high certainty. The two together came out at 0.91, from 0.84 to 0.99, also high certainty, which is a real effect and a very small one.

An earlier meta-analysis reached the opposite conclusion, and the reason is not hidden. Counting people in care homes alongside people at home, calcium with vitamin D cut hip fractures by 30 per cent. The newer pool is different. It is 87 per cent trials of people living at home, and 73 per cent trials of people who were not at high risk of fractures or falls. Its authors say directly that for those at high risk or in residential care the evidence is thin.

Unsettled. So the two reviews are not describing the same person, and that is the most likely reason they disagree. The 30 per cent came from a pool with care home residents in it, people who break hips often enough for a small relative change to show up. The null came from a pool that is mostly people living at home and mostly people who were not at high risk to begin with. Which of those is closer to you decides which number is closer to your answer, and the newer review is explicit that at the frail end it does not have the evidence to say. Nobody can hand you a single figure here, and anyone who does is choosing one of these pools without telling you.

Two more results point the same way for people living at home. Across 33 randomised trials in community-dwelling adults over 50, neither calcium nor vitamin D nor the two together lowered the risk of a hip fracture. And in postmenopausal women who already have osteoporosis, eleven trials of calcium with vitamin D moved bone density only at the pelvis and did not reduce fractures at all.

Not for everyone. In the Women's Health Initiative itself, calcium with vitamin D raised kidney stones by 17 per cent. If you have ever had a stone, that is the number that should decide this for you rather than the cardiovascular argument, and the upper limit for calcium was set partly on that evidence.

What to do with this

If you get your calcium from food

Nothing on this page asks anything of you. The requirement is 1,000 mg a day for most adults and 1,200 mg for women over 50 and everyone over 70. Dairy, fortified plant drinks, tinned fish with bones, tofu set with calcium and greens other than spinach will cover it. Absorption is about 27 per cent from milk against about 5 per cent from spinach, so the greens that count are the low-oxalate ones.

If you take a supplement you were prescribed

Keep taking it and ask your clinician at the next appointment. People treated for osteoporosis, people on long-term steroids and people who have had bariatric surgery are taking it for a reason that outweighs a borderline cardiovascular signal.

If you take a supplement you chose yourself

Work out what you already get from food first. About one American in four takes a calcium-containing supplement on a given day, and among those who do it averages 521 mg, which is half the daily requirement arriving in a single dose on top of meals. Someone who adds a 1,000 mg tablet to a diet that was already close to the requirement is buying the risk without needing the benefit. If you do need to top up, a dose of 500 mg or less taken with food is absorbed better and is the version the trials that worried people did not test.

Not for everyone. Keep calcium carbonate at least four hours away from levothyroxine, because it interferes with absorbing the thyroid hormone. The same applies to iron tablets and to tetracycline and quinolone antibiotics.

What would change this answer

• A trial designed to measure cardiovascular events as its primary outcome, rather than counting them inside a bone trial. Nobody has run one, and given the size and length it would need, nobody is likely to.
• A trial that separates calcium from vitamin D. Every large result above gave them together, and that is the specific reason the Women's Health Initiative authors say their finding cannot be attributed to either one.
• Trials of the dose people are now advised to take. The trials that produced the alarm used 1,000 mg or more in a single daily dose. Whether 500 mg with a meal carries the same signal is unknown.

How we searched

Sources

1. ca-h01 · Randomised controlled trial(s) · post hoc analysis of long-term follow-up of a randomised trial · n = 36,282
   For women randomly assigned to CaD versus placebo, a 7% reduction in cancer mortality was observed after a median cumulative follow-up of 22.3 years (1817 vs. 1943 deaths; hazard ratio [HR], 0.93 [95% CI, 0.87 to 0.99]), along with a 6% increase in CVD mortality (2621 vs. 2420 deaths; HR, 1.06 [CI, 1.01 to 1.12]). There was no overall effect on other measures, including all-cause mortality (7834 vs. 7748 deaths; HR, 1.00 [CI, 0.97 to 1.03]).
   
   Who: postmenopausal women in the United States with no history of breast or colorectal cancer
   Effect: cancer mortality hazard ratio 0.93 (95% CI 0.87 to 0.99); cardiovascular mortality 1.06 (1.01 to 1.12); all-cause mortality 1.00 (0.97 to 1.03)
   Certainty: post hoc analysis of a trial that ran for 7 years and was then followed for 22
   Thomson et al., Annals of Internal Medicine, 2024 · checked 2026-09-16 · we read the abstract
2. ca-h02 · Randomised controlled trial(s) · post hoc analysis of long-term follow-up of a randomised trial · n = 36,282
   LIMITATION: Hip fracture and CVD outcomes were available on only a subset of participants, and effects of calcium versus vitamin D versus joint supplementation could not be disentangled.
   
   Who: postmenopausal women in the Women's Health Initiative
   Effect: calcium, vitamin D and the combination cannot be told apart in this design
   Certainty: stated limitation of the analysis
   Thomson et al., Annals of Internal Medicine, 2024 · checked 2026-09-16 · we read the abstract
3. ca-h03 · Meta-analysis or systematic review · meta-analysis of double-blind, placebo-controlled randomised trials · n = 28,935 treated and 14,243 control
   Calcium supplements significantly increased the risk of CVD (RR 1.15, 95% CI 1.06-1.25], I2 = 0.0%, n = 14) and CHD (RR 1.16, 95% CI 1.05-1.28], I2 = 0.0%, n = 9) in double-blind, placebo-controlled RCTs, specifically in healthy postmenopausal women.
   
   Who: mostly healthy postmenopausal women
   Effect: cardiovascular disease relative risk 1.15 (95% CI 1.06 to 1.25); coronary heart disease 1.16 (1.05 to 1.28); no heterogeneity
   Certainty: no heterogeneity between trials, but the trials were designed to study bone rather than the heart
   Myung et al., Nutrients, 2021 · checked 2026-09-16 · we read the abstract
4. ca-h04 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials · n = 12 trials
   Calcium supplementation was not associated with myocardial infarction, total stroke, heart failure admission, and cardiovascular/all-cause mortality. Further studies are required to examine and understand these associations.
   
   Who: participants of 12 randomised trials of calcium supplementation
   Effect: no association with myocardial infarction, total stroke, heart failure admission or all-cause and cardiovascular mortality, and subgroup analyses did not change it
   Certainty: authors call for further study
   Yang et al., Heart, Lung and Circulation, 2023 · checked 2026-09-16 · we read the abstract
5. ca-h05 · Observational data · systematic review and dose-response meta-analysis of prospective cohort studies · n = 163,657 deaths, of which 83,703 cardiovascular
   Dietary calcium intake was associated with a lower risk of all-cause mortality (Pooled ES for highest v lowest category: 0.95; 95% CI: 0.92-0.99, I2=62.1%, P < 0.001). Supplemental calcium intake was not significantly associated with risk of all-cause, CVD and cancer mortality.
   
   Who: adults followed for 4.2 to 28 years in 36 publications
   Effect: total calcium intake and cardiovascular mortality pooled effect 0.91 (95% CI 0.83 to 0.99); dietary calcium and all-cause mortality 0.95 (0.92 to 0.99); supplemental calcium not significantly associated with any of them
   Certainty: observational data, substantial heterogeneity, non-linear dose response
   Asemi et al., Critical Reviews in Food Science and Nutrition, 2022 · checked 2026-09-16 · we read the abstract
6. ca-h06 · Meta-analysis or systematic review · systematic review of randomised trials commissioned for a national recommendation · n = 739,803
   Limited evidence suggested some supplements may be associated with higher risk of serious harms (hip fracture [vitamin A], hemorrhagic stroke [vitamin E], and kidney stones [vitamin C, calcium]).
   
   Who: adults without cardiovascular disease or cancer and without known deficiencies, 84 studies
   Effect: little or no benefit overall; limited evidence of higher risk of kidney stones with calcium and vitamin C, hip fracture with vitamin A, haemorrhagic stroke with vitamin E
   Certainty: evidence report for the US Preventive Services Task Force
   O'Connor et al., JAMA, 2022 · checked 2026-09-16 · we read the abstract
7. ca-02 · Position of an expert body
   Ages 19–50: 1,000 mg; Men 51–70: 1,000 mg; Women 51+: 1,200 mg; Adults 71+: 1,200 mg
   
   Who: adults
   Effect: 1,000 or 1,200 mg per day by age and sex
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
8. ca-03 · Position of an expert body
   Ages 19–50: 2,500 mg; Ages 51–70: 2,000 mg; Ages >70: 2,000 mg
   
   Who: adults
   Effect: UL 2,500 then 2,000 mg/day
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
9. ca-04 · Position of an expert body
   Absorption of calcium from food is about 45% at intakes of 200 milligrams (mg)/day but only 15% when intakes are higher than 2,000 mg/day.
   
   Who: adults
   Effect: absorption falls as intake rises
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
10. ca-05 · Position of an expert body
    Absorption from supplements is highest with doses of 500 mg or less. For example, the body absorbs about 36% of a 300 mg calcium dose and 28% of a 1,000 mg dose.
    
    Who: adults
    Effect: 36% vs 28% absorbed
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
11. ca-06 · Position of an expert body
    Absorption of calcium is only 5% for spinach, whereas it is much higher, at 27%, for milk.
    
    Who: general
    Effect: 5% vs 27% absorption
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
12. ca-07 · Randomised controlled trial(s)
    Not all clinical trials have found that these supplements improve bone health or reduce the risk of fractures in this population.
    
    Who: older adults
    Effect: inconsistent effect on fractures
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
13. ca-08 · Meta-analysis or systematic review
    A meta-analysis of 14 RCTs (including one study that administered supplements providing 20 mcg [800 IU] vitamin D per day) in 28,935 healthy postmenopausal women found that calcium supplements providing 500 to 2,000 mg/day calcium for 1 to 7 years increased CVD risk by 15% and coronary heart disease risk by 16%
    
    Who: healthy postmenopausal women
    Effect: +15% CVD risk, +16% coronary heart disease
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
14. ca-09 · Position of an expert body
    An expert panel convened by the National Osteoporosis Foundation and American Society for Preventive Cardiology determined, on the basis of moderate-quality evidence, that calcium intakes with or without vitamin D from foods or supplements neither increase nor decrease the risk of CVD or CVD mortality.
    
    Who: general adults
    Effect: no change in CVD risk
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
15. ca-10 · Observational data
    The ULs for calcium...are based on observational evidence from the WHI showing a link between higher intakes of supplemental calcium (1,000 mg/day for 7 years) and a greater risk of kidney stones.
    
    Who: postmenopausal women in the WHI
    Effect: higher kidney stone risk
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
16. ca-11 · Position of an expert body
    Calcium carbonate supplements can interfere with the absorption of levothyroxine...The FDA-approved label for this medication instructs patients who are taking calcium carbonate supplements to avoid taking levothyroxine within 4 hours of taking the supplement.
    
    Who: people taking levothyroxine
    Effect: reduced drug absorption
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Calcium · checked 2026-09-15
17. vitd-b06 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis, GRADE assessed · n = 49,853 across nine trials
    There is high quality evidence that vitamin D plus calcium results in a small reduction in hip fracture risk (nine trials, 49,853 participants; RR 0.84, 95% confidence interval (CI) 0.74 to 0.96; P value 0.01). In low-risk populations (residents in the community: with an estimated eight hip fractures per 1000 per year), this equates to one fewer hip fracture per 1000 older adults per year (95% CI 0 to 2). In high risk populations (residents in institutions: with an estimated 54 hip fractures per 1000 per year), this equates to nine fewer hip fractures per 1000 older adults per year (95% CI 2 to 14).
    
    Who: post-menopausal women and older men; community residents versus institution residents
    Effect: hip fracture relative risk 0.84 (95% CI 0.74 to 0.96); absolute effect one fewer hip fracture per 1,000 per year in the community (95% CI 0 to 2) and nine fewer per 1,000 per year in institutions (95% CI 2 to 14)
    Certainty: high quality evidence (GRADE)
    Avenell et al., Cochrane Database of Systematic Reviews, 2014 · checked 2026-09-16 · we read the abstract
18. vitd-b07 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis · n = up to 71,032 participants depending on the outcome
    Hypercalcaemia, which was usually mild (2.6 to 2.8 mmol/L), was more common in people receiving vitamin D or an analogue, with or without calcium (21 trials, 17,124 participants, RR 2.28, 95% CI 1.57 to 3.31)... There was also a small increased risk of gastrointestinal symptoms (15 trials, 47,761 participants, RR 1.04, 95% CI 1.00 to 1.08)... and a significant increase in renal disease (11 trials, 46,548 participants, RR 1.16, 95% CI 1.02 to 1.33).
    
    Who: post-menopausal women and older men in trials of vitamin D with or without calcium
    Effect: renal disease relative risk 1.16 (95% CI 1.02 to 1.33, 11 trials, n=46,548); hypercalcaemia 2.28 (1.57 to 3.31, 21 trials, n=17,124); gastrointestinal symptoms 1.04 (1.00 to 1.08); mortality 0.97 (0.93 to 1.01)
    Certainty: not separately graded in the abstract
    Avenell et al., Cochrane Database of Systematic Reviews, 2014 · checked 2026-09-16 · we read the abstract
19. vitd-b09 · Randomised controlled trial(s) · randomised controlled trial · n = 36,282
    Intention-to-treat analysis indicated that participants receiving calcium plus vitamin D supplementation had a hazard ratio of 0.88 for hip fracture (95 percent confidence interval, 0.72 to 1.08), 0.90 for clinical spine fracture (0.74 to 1.10), and 0.96 for total fractures (0.91 to 1.02). The risk of renal calculi increased with calcium plus vitamin D (hazard ratio, 1.17; 95 percent confidence interval, 1.02 to 1.34). Censoring data from women when they ceased to adhere to the study medication reduced the hazard ratio for hip fracture to 0.71 (95 percent confidence interval, 0.52 to 0.97).
    
    Who: postmenopausal women aged 50 to 79 in the Women's Health Initiative
    Effect: hip fracture hazard ratio 0.88 (95% CI 0.72 to 1.08); total fractures 0.96 (0.91 to 1.02); kidney stones 1.17 (1.02 to 1.34); hip fracture 0.71 (0.52 to 0.97) when data are censored at the point women stopped taking the tablets
    Certainty: single large trial; the adherence analysis is secondary
    Jackson et al., New England Journal of Medicine, 2006 · checked 2026-09-16 · we read the abstract
20. ca-12 · Position of an expert body
    Calcium deficiency can reduce bone strength and lead to osteoporosis, which is characterized by fragile bones and an increased risk of falling.
    
    Who: adults with chronically low calcium intake
    Effect: reduced bone strength, osteoporosis
    NIH Office of Dietary Supplements, Calcium - Health Professional Fact Sheet · checked 2026-09-16 · we read the full text
21. ca-13 · Position of an expert body
    Another effect of chronic calcium deficiency is osteomalacia, or defective bone mineralization and bone softening, which can occur in adults and children.
    
    Who: adults and children with chronic deficiency
    Effect: defective bone mineralisation and softening
    NIH Office of Dietary Supplements, Calcium - Health Professional Fact Sheet · checked 2026-09-16 · we read the full text
22. ca-t1 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised controlled trials of calcium, vitamin D or both against placebo or no treatment, in adults not already on osteoporosis drugs · n = 69 trials with 153,902 participants; 9,067 in the calcium-only fracture analysis
    For the primary outcome of any fracture, little to no effect was found from use of calcium supplements (11 trials, 9067 participants; risk ratio 0.91, 95% confidence interval 0.81 to 1.01; moderate certainty), vitamin D supplements (36 trials, 92 045 participants; 1.00, 0.95 to 1.06; high certainty), or combined supplementation (15 trials, 51 126 participants; 0.91, 0.84 to 0.99; high certainty).
    
    Who: adults aged 18 and over, 87 per cent community dwelling and 73 per cent not at high risk of fracture or falls
    Effect: any fracture risk ratio 0.91 (95% CI 0.81 to 1.01) for calcium alone (11 trials, moderate certainty), 1.00 (95% CI 0.95 to 1.06) for vitamin D alone (36 trials, high certainty) and 0.91 (95% CI 0.84 to 0.99) for the two combined (15 trials, high certainty)
    Certainty: the combined estimate is nominally significant but the authors judged the absolute risk reduction below the threshold they had set as clinically meaningful; findings held across extensive subgroup analysis
    Bolland et al., BMJ, 2026 · checked 2026-09-17 · we read the abstract
23. ca-t2 · Meta-analysis or systematic review · description of the trial population and the authors' own statement of the evidence gap, within the same systematic review · n = 153,902 participants across the 69 trials
    Participants in most of the trials were community dwelling (87%) and not at high risk of fractures or falls (73%)...Evidence for high risk patients or those requiring residential care was limited for many outcomes for calcium monotherapy and for combined supplementation.
    
    Who: the 69 included trials, characterised by living situation and baseline fracture risk
    Effect: 87 per cent of trials recruited community-dwelling participants and 73 per cent recruited people not at high risk of fractures or falls
    Certainty: this is a limitation of the evidence base, not a measured effect: the review states outright that evidence for high-risk patients and those in residential care was limited for many outcomes
    Bolland et al., BMJ, 2026 · checked 2026-09-17 · we read the abstract
24. ca-t3 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised clinical trials against placebo or no treatment · n = 51,145 participants
    There was no significant association of calcium or vitamin D with risk of hip fracture compared with placebo or no treatment (calcium: RR, 1.53 [95% CI, 0.97 to 2.42]; ARD, 0.01 [95% CI, 0.00 to 0.01]; vitamin D: RR, 1.21 [95% CI, 0.99 to 1.47]; ARD, 0.00 [95% CI, -0.00 to 0.01]. There was no significant association of combined calcium and vitamin D with hip fracture compared with placebo or no treatment (RR, 1.09 [95% CI, 0.85 to 1.39]; ARD, 0.00 [95% CI, -0.00 to 0.00]).
    
    Who: community-dwelling adults older than 50 years in 33 randomised trials
    Effect: hip fracture risk ratio 1.53 (95% CI 0.97 to 2.42) for calcium, 1.21 (95% CI 0.99 to 1.47) for vitamin D and 1.09 (95% CI 0.85 to 1.39) for the combination, with absolute risk differences of 0.01 or less
    Certainty: all three point estimates sit above 1.0, so nothing here suggests protection; results held regardless of dose, sex, fracture history, dietary calcium intake or baseline vitamin D, but the review covers only people living at home
    Zhao et al., JAMA, 2017 · checked 2026-09-17 · we read the abstract
25. ca-t4 · Meta-analysis or systematic review · meta-analysis of randomised controlled trials of calcium plus vitamin D supplementation and fracture incidence · n = 30,970 participants, with 195 hip fractures and 2,231 total fractures
    Meta-analysis of all studies showed that calcium plus vitamin D supplementation produced a statistically significant 15 % reduced risk of total fractures (SRRE, 0.85; 95 % confidence interval [CI], 0.73-0.98) and a 30 % reduced risk of hip fractures (SRRE, 0.70; 95 % CI, 0.56-0.87).
    
    Who: middle-aged to older adults, both community-dwelling and institutionalised, in eight randomised trials
    Effect: total fractures summary relative risk 0.85 (95% CI 0.73 to 0.98) and hip fractures 0.70 (95% CI 0.56 to 0.87)
    Certainty: directly contradicts the 2017 and 2026 reviews; the authors name as a limitation that the analysis used data from a subgroup analysis of the Women's Health Initiative, and only 195 hip fractures underpin the headline figure, so the estimate is fragile
    Weaver et al., Osteoporosis International, 2016 · checked 2026-09-17 · we read the abstract
26. ca-t5 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised controlled trials of combined calcium and vitamin D supplementation · n = 43,869 participants; the fracture pooling of three large trials covered over 42,000
    Combined supplementation modestly improved BMD at the pelvis (SMD = 0.20, 95% CI: 0.05–0.35, p = 0.01) without significant changes in BMD at the lumbar spine, femoral neck, or total hip. The overall fracture risk was not significantly reduced (RR = 0.98, 95% CI: 0.89–1.07, p = 0.68).
    
    Who: postmenopausal women with diagnosed osteoporosis in eleven randomised trials
    Effect: pelvic bone mineral density standardised mean difference 0.20 (95% CI 0.05 to 0.35, p = 0.01) with no change at lumbar spine, femoral neck or total hip; overall fracture risk ratio 0.98 (95% CI 0.89 to 1.07, p = 0.68) and 0.95 (95% CI 0.85 to 1.07) in the three large trials
    Certainty: a standardised mean difference of 0.20 at one site only is a small effect and not matched by any fracture benefit; the authors call for larger high-dose trials with adjudicated fracture endpoints
    BMC Musculoskeletal Disorders, 2025 · checked 2026-09-17 · we read the abstract
27. ca-c1-08 · Position of an expert body · national dietary surveillance including a 24-hour supplement recall · n = 1,883 reporters of calcium-containing supplements
    The average intake of calcium from multi- or single ingredient supplements was 521 mg (3).
    
    Who: US individuals aged 2 and over, excluding pregnant and lactating women and breast-fed children, WWEIA/NHANES 2009-2010
    Effect: 26% reported a calcium-containing supplement on a given day; mean supplemental calcium 521 mg; women and people over 60 took more
    Certainty: one day of recall, so it describes who took what that day rather than habitual use; it says nothing about whether the supplement helped
    FSRG Dietary Data Briefs, USDA Agricultural Research Service, WWEIA/NHANES 2009-2010 · checked 2026-09-18 · we read the section
28. ca-c1-13 · Observational data · two prospective cohort studies with food frequency questionnaires, multivariable survival models · n = 106,772 people; 22,318 fractures including 5,425 hip fractures
    For every glass of milk in women no reduction was observed in fracture risk with higher milk consumption for any fracture (1.02, 1.00 to 1.04) or for hip fracture (1.09, 1.05 to 1.13).
    
    Who: 61,433 Swedish women followed 20 years and 45,339 Swedish men followed 11 years
    Effect: per glass of milk in women: any fracture hazard ratio 1.02 (95% CI 1.00 to 1.04), hip fracture 1.09 (1.05 to 1.13); in men 1.01 (0.99 to 1.03) and 1.03 (0.99 to 1.07)
    Certainty: observational; the authors themselves ask for cautious reading because reverse causation and residual confounding cannot be excluded — people warned about fragile bones drink more milk
    Michaëlsson et al., BMJ, 2014 · checked 2026-09-18 · we read the abstract
29. ca-c1-14 · Observational data · prospective cohort with a 96-item food frequency questionnaire validated against four seven-day food records · n = 106,772 people
    Instructions were given that one serving of milk corresponded to one glass of 200 mL.
    
    Who: 61,433 Swedish women and 45,339 Swedish men
    Effect: one reported serving of milk was defined as one glass of 200 mL; questionnaire-to-food-record correlation for milk intake about 0.7
    Certainty: a definition, not a result: it matters because the widely quoted '3 glasses a day' headline is meaningless without it
    Michaëlsson et al., BMJ, 2014 · checked 2026-09-18 · we read the fulltext
30. ca-c1-15 · Observational data · authors' own statement of the evidence gap in the discussion of their cohort study · n = no randomised trial exists
    The fact that no randomised trial has examined the effect of milk intake on incidence of mortality and fractures, long term experimental evidence is needed to confirm a causal association between higher milk intake and higher mortality.
    
    Who: the whole literature on milk intake, mortality and fracture
    Effect: the authors state plainly that long-term experimental evidence would be needed to call the association causal, and that Mendelian randomisation on lactase persistence is a weak instrument here
    Certainty: this is the limitation section of one study, not a systematic search for trials; but nothing we found in the corpus contradicts it
    Michaëlsson et al., BMJ, 2014 · checked 2026-09-18 · we read the fulltext