Do Calcium Supplements Prevent Fractures? What the Evidence Says

Do calcium supplements prevent fractures?

For most healthy, community-dwelling adults, the trial evidence does not show that calcium supplements prevent fractures — but that is not the same as saying calcium does not matter. The answer changes completely depending on the population studied, whether vitamin D was given alongside, and whether people actually kept taking the tablets.

Three questions get collapsed into one in most coverage: does supplementation raise bone density (usually yes, slightly), does it reduce fractures (much less certain), and is adequate calcium necessary for bone health and for osteoporosis treatment to work (yes). For the practical version, see our guide to whether you need calcium supplements. What follows is the evidence itself.

What did the biggest trial in healthy postmenopausal women find?

The Women's Health Initiative gave 36,282 postmenopausal women calcium plus vitamin D for seven years and did not significantly reduce hip fracture. Women aged 50 to 79 were randomly assigned to 1,000mg of elemental calcium as calcium carbonate with 400 IU of vitamin D3 daily, or to placebo, with fractures tracked for an average of 7.0 years. Hip bone density ended 1.06% higher in the supplement group — but on intention-to-treat analysis the hazard ratio was 0.88 for hip fracture (95% CI 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): pointing in the right direction, none statistically significant. The authors concluded that in healthy postmenopausal women, calcium with vitamin D produced "a small but significant improvement in hip bone density, did not significantly reduce hip fracture, and increased the risk of kidney stones." Jackson RD et al., New England Journal of Medicine, 2006

One detail recurs throughout this literature. When the analysis censored data from women once they stopped taking the study medication, the hip-fracture hazard ratio fell to 0.71 (95% CI 0.52 to 0.97). Jackson RD et al., New England Journal of Medicine, 2006 That is not proof of benefit — people who stick with treatment differ from those who don't — but it means the null headline is partly a story about adherence.

What happens when you pool all the community trials?

A 2017 JAMA meta-analysis of 33 randomised trials in 51,145 community-dwelling adults over 50 found no lower fracture risk. For the primary outcome of hip fracture, the reported risk ratios compared with placebo or no treatment were 1.53 for calcium, 1.21 for vitamin D and 1.09 for combined calcium and vitamin D — and the authors' own summary of those numbers was that supplement use "was not associated with a significant difference in the risk of hip fractures compared with placebo or no treatment". Zhao JG et al., JAMA, 2017

Those ratios sit above 1.0, but the authors did not present them as evidence of harm — reporting no significant difference means the uncertainty around each estimate was compatible with no effect. Their stated conclusion was that the use of supplements that included calcium, vitamin D, or both, compared with placebo or no treatment, "was not associated with a lower risk of fractures among community-dwelling older adults", and they went further — "These findings do not support the routine use of these supplements in community-dwelling older people." Zhao JG et al., JAMA, 2017

The UK's own contribution points the same way. The RECORD trial randomised 5,292 people aged 70 and over who had already sustained a low-trauma fracture — a group at high risk of another — to vitamin D3, calcium, both or placebo, recruiting them from 21 UK hospitals, and found no significant differences in new low-trauma fracture rates. Its investigators concluded that the findings did not support routine oral supplementation with calcium and vitamin D3, alone or in combination, in this population. RECORD trial, The Lancet, 2005

Why did an earlier trial in very elderly women show a large benefit?

Because those women had far more to gain: the treatment measurably corrected a deficit rather than topping up an adequate diet. A 1992 trial gave 3,270 healthy ambulatory women with a mean age of 84 either 1.2g of elemental calcium plus 800 IU of vitamin D3 daily or placebo for 18 months. Among those who completed it, hip fractures were 43% lower and total non-vertebral fractures 32% lower than in the placebo group, with analyses by active treatment and by intention to treat reported as similar. Proximal femur bone density rose 2.7% while falling 4.6% on placebo. Crucially, in the treated group mean parathyroid hormone fell 44% and serum 25-hydroxyvitamin D rose 162% above baseline. The authors concluded that supplementation with vitamin D3 and calcium reduces the risk of hip fractures and other non-vertebral fractures among elderly women. Chapuy MC et al., New England Journal of Medicine, 1992

Those two numbers are the mechanistic clue. A 162% rise in vitamin D and a 44% fall in parathyroid hormone describe a deficiency being switched off — the parathyroid glands had been pulling calcium out of the skeleton, and the supplements stopped them. Give the same tablets to a 58-year-old who already eats dairy and takes vitamin D in winter, and there is no such process to switch off.

How do the main trials compare?

Trial / analysis	Population	Intervention	Fracture result
Chapuy 1992 (NEJM)	3,270 ambulatory women, mean age 84	1.2g calcium + 800 IU vitamin D3, 18 months	Hip fractures 43% lower; non-vertebral 32% lower (completers)
RECORD 2005 (Lancet)	5,292 UK adults 70+ with a previous low-trauma fracture	Vitamin D3, calcium, both, or placebo	No significant difference in new fractures
WHI 2006 (NEJM)	36,282 postmenopausal women aged 50–79	1,000mg calcium + 400 IU vitamin D3, 7 years	Hip fracture HR 0.88 (0.72–1.08); not significant
Zhao 2017 (JAMA)	51,145 community-dwelling adults 50+, 33 trials	Calcium, vitamin D, or both	No lower fracture risk

Does it matter whether calcium is taken with vitamin D?

Yes — the combined evidence is stronger than the evidence for calcium on its own, and that is how UK guidance is written. The National Osteoporosis Guideline Group states that, with respect to combined calcium and vitamin D supplements, "meta-analyses have reported reduction in hip and non-vertebral fractures, and possibly also in vertebral fractures", grading that at evidence level Ia. National Osteoporosis Guideline Group (NOGG) That Ia-graded statement is specifically about the combination, not about calcium taken alone — and in Zhao's pooled analysis calcium alone had the least favourable hip-fracture figure of the three options.

Even that pooled positive evidence is contested, and an evidence review should say so. A 2016 meta-analysis from the National Osteoporosis Foundation pooled eight trials with 30,970 participants and found a statistically significant 15% reduction in total fractures (summary relative risk 0.85, 95% CI 0.73 to 0.98) and a 30% reduction in hip fractures (0.70, 0.56 to 0.87), concluding that the evidence supported calcium plus vitamin D in both community-dwelling and institutionalised middle-aged to older adults. Its own stated limitation was that it used data from a subgroup analysis of the Women's Health Initiative. Weaver CM et al., Osteoporosis International, 2016 The same journal then published a letter from Avenell, Bolland, Grey and Reid titled "Further major uncorrected errors in National Osteoporosis Foundation meta-analyses of calcium and vitamin D supplementation in fracture prevention". Avenell A et al., Osteoporosis International, 2017

So a widely cited analysis in support of supplementation was formally challenged in its own journal. Combining calcium with vitamin D remains the better-supported route — our vitamin D for bone health guide covers UK dosing — but the fracture benefit is not settled.

So why does UK guidance still recommend calcium and vitamin D?

Because adequate calcium and vitamin D is the foundation the osteoporosis medicines were proven on, not a substitute for them. NOGG makes the point directly: "Most randomised controlled trials of anti-resorptive and anabolic drugs … have included co-administration of calcium and vitamin D supplements." National Osteoporosis Guideline Group (NOGG) Those trials were run against a background of calcium and vitamin D supplementation. We do not know that osteoporosis treatment works the same way in someone whose intake is inadequate.

The guidance then sets out the practical position. NOGG puts the UK Reference Nutrient Intake at 700mg of calcium a day for adults aged 19 years and older, and the NHS gives the same 700mg figure for adults aged 19 to 64. National Osteoporosis Guideline Group (NOGG) NHS NOGG is explicit about the route: "In clinical practice, dietary sources of calcium are the preferred option and calcium (combined with vitamin D) supplementation should be targeted to those who do not get sufficient calcium from their diet", and it names those who are "housebound or living in residential or nursing care" as more likely to require supplementation to reach the recommended intake. National Osteoporosis Guideline Group (NOGG) The Royal Osteoporosis Society adds the adjustment most people ask about: if you are at risk of osteoporosis or taking a medicine for it, your doctor may advise increasing intake to around 1,000mg a day. Royal Osteoporosis Society

Do the fracture trials show any harms?

They do, and the clearest one came out of a fracture trial rather than a safety study: kidney stones. In the Women's Health Initiative, the risk of renal calculi increased with calcium plus vitamin D, with a hazard ratio of 1.17 (95% CI 1.02 to 1.34) — a small but statistically significant excess in a trial that did not significantly reduce hip fracture. Jackson RD et al., New England Journal of Medicine, 2006 RECORD adds the more mundane problem: people stop taking calcium, and gastrointestinal side effects are part of why. RECORD trial, The Lancet, 2005 The Royal Osteoporosis Society's warning sits in the same place: more than 1,500mg of calcium supplements a day can cause stomach pain, diarrhoea and lead to kidney stones. Royal Osteoporosis Society

We cover the dose ceiling and the wider safety debate in how much calcium is too much. The point here is narrower: in the trial where harm was measured most precisely, the harm was significant and the fracture benefit was not.

What should you actually do with this?

Aim for 700mg of calcium a day, preferably from food, alongside the vitamin D your body needs to use it — and treat a supplement as a way of closing a measured gap rather than as insurance. If your fracture risk is high, the intervention that changes outcomes is the one your GP prescribes, with calcium and vitamin D as the foundation underneath it. Our guides to fracture risk and FRAX and hip fracture prevention cover what moves the needle.

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This article is part of our bone health series and is an evidence review, not personal medical advice. Discuss any supplement — and any change to osteoporosis treatment — with your GP.