THE BMJ REVIEW
A new systematic review published in The BMJ analysed 69 randomised controlled trials involving 153,902 participants. The conclusion: calcium supplements, vitamin D supplements, and the combination of the two provide little to no clinically meaningful benefit for preventing fractures or falls in most older adults.
For a category of supplements widely recommended by doctors and used by millions, that's significant. The conclusion sounds unambiguous, but the study doesn’t highlight two important things. First, it did not assess participants' digestive capacity, which is known to decline with age and which directly affects how well calcium can be absorbed. Second, it did not separately analyse the form of calcium used in each trial. Not all calcium sources are equally absorbent, and the trials reviewed used conventional salt forms (mostly calcium carbonate and calcium citrate) — not newer, more bioavailable forms such as ionic calcium.
But the study also contains important nuances that have been largely missed in the headlines, and those nuances matter if you take calcium for bone health, or are thinking about it.
REVIEW FINDINGS
What the Study Actually Showed
For each intervention, the review found:
Calcium alone (11 trials, 9,067 participants): A small directional trend toward fewer fractures (risk ratio 0.91), but the confidence interval crossed 1.00: meaning the result was not statistically meaningful. Effects on hip fracture, falls, and vertebral fracture were similarly inconclusive.
Vitamin D alone (36 trials, 92,045 participants): Essentially no effect on any fracture outcome (risk ratio 1.00). This was rated high-certainty evidence and the most confident result in the entire review.
Calcium and vitamin D combined (15 trials, 51,126 participants): A statistically significant 9% reduction in any fracture (risk ratio 0.91, 95% CI 0.84 to 0.99). In absolute terms, however, this worked out to roughly 1% fewer fractures, which is below the threshold the authors had pre-defined as clinically meaningful. The signal also weakened substantially when one outlier trial (Chapuy 1992, conducted in very high-risk French nursing-home residents with severe vitamin D deficiency) was removed from the analysis.
THE LIMITATIONS
The Limitations the Authors Themselves Flagged
What's striking about the paper, and what tends to get lost in summary coverage, is how candidly the authors discuss the constraints of the underlying trials. Several limitations are worth understanding before drawing broader conclusions about calcium itself, as opposed to calcium as it was tested.
Most trials did not study high-risk people
Of the 69 trials, 87% enrolled community-dwelling adults, and 73% did not target people at high risk of fractures or falls. Only 3% of trials reported mean baseline vitamin D levels below 25 nmol/L — the threshold at which calcium absorption becomes seriously impaired. The biggest historical benefit ever shown (Chapuy 1992) was in women averaging 84 years old, severely vitamin D deficient, with dietary calcium intakes around 513 mg/day. That population is not who is typically buying calcium tablets at a pharmacy.
Control-group contamination was widespread
The authors note that "almost all studies either allowed participants to take non-trial supplements or did not clearly report instructions for avoiding non-trial supplementation." If placebo-group participants were quietly taking their own calcium and vitamin D — which is plausible given how widely these are recommended — the trials would systematically underestimate any real effect.
Tolerance was a real-world problem
The discussion section is blunt: calcium supplements "are often difficult to swallow and poorly tolerated in older adults, commonly causing gastrointestinal adverse effects such as constipation, bloating, abdominal pain, or cramps." A previous analysis cited in the paper suggested possible increases in gastrointestinal-related hospital admissions linked to calcium supplements. The Women's Health Initiative also found increased kidney stone incidence with combined supplementation, and a 10–20% relative increase in myocardial infarction has been reported in some calcium-supplement meta-analyses (though others have not replicated this).
The form of calcium varied enormously and was not analysed separately
The review applied "no restrictions on type or dose of calcium." The included trials used calcium carbonate, calcium citrate, and other conventional calcium salt forms. The review did not, and was not designed to, compare absorption differences between calcium sources, or to test whether more bioavailable forms produced different outcomes.
This last point is, in some ways, the most important for consumers.
THE ABSORPTION QUESTION
The Absorption Question the Study Didn't Ask
Calcium carbonate, the most commonly studied form, requires stomach acid to dissociate before any calcium becomes available for absorption. Older adults, the population most often targeted for bone-health supplementation, frequently have reduced gastric acid production (aka reduced digestion). Many also take acid-suppressing medications such as proton pump inhibitors or H2 blockers, which further impair absorption. Calcium carbonate then needs adequate vitamin D status to be efficiently transported across the intestinal wall via the active calbindin pathway.
ABSORPTION CHAIN
IN OTHER WORDS
In other words, the trials in the BMJ review tested a model that goes roughly like this: take a calcium salt, hope the stomach acid breaks it down, hope vitamin D status is sufficient to transport it, hope it reaches bone. There are multiple failure points in that chain.
SEPARATE QUESTION
This is a separate question from whether calcium itself matters for bone, which observational data consistently suggest it does. The question is whether the delivery system used in most trials is fit for purpose.
IONIC CALCIUM
IONIC CALCIUM
Some calcium sources bypass parts of this chain. Ionic calcium: calcium already in its dissociated, charged form (Ca²⁺), does not require gastric acid to become bioavailable. Absorption research suggests ionic forms can use passive (paracellular) absorption pathways that are less dependent on vitamin D status than the active (transcellular) pathway. Proprietary ionic calcium formulations such as the SAC® formula, used in Marah Natural, are built around this principle.
TO BE CLEAR
To be clear: no large randomised trial has tested whether ionic calcium changes fracture outcomes, and the BMJ review does not speak to that question either way. But it does underscore that "calcium supplementation" as a category is not one thing and that the trials we have should not be read as a verdict on every calcium source.
WHY THE FORM OF CALCIUM MATTERS
Why the Form of Calcium Matters
CALCIUM CARBONATE
IONIC CALCIUM
Calcium carbonate, the most studied form, needs two things to work. Stomach acid to dissociate it, and adequate vitamin D status to transport it across the intestinal wall.
In older adults, both are often in short supply.
Ionic calcium works differently. It's calcium already in its dissociated form (Ca²⁺): the form the body absorbs. It doesn't need to be broken down by stomach acid, and absorption research suggests it can use passive pathways less dependent on vitamin D status.
The SAC® formula in Marah Natural is built around this principle. No large trial has yet tested ionic calcium specifically for fracture outcomes, but the BMJ review makes clear that "calcium supplementation" is not one thing, and the trials we have shouldn't be read as a verdict on every calcium source.
PRACTICAL TAKEAWAYS
What This Means if You Take Calcium
A few honest takeaways from the BMJ review, framed for the general reader:
For most healthy adults eating a reasonable diet, routine calcium and vitamin D supplementation is unlikely to meaningfully reduce fracture risk. This is what the evidence says. Food sources of calcium: dairy, leafy greens, sardines, almonds, fortified plant milks — remain the foundation, and the strongest non-drug interventions for fracture prevention are resistance exercise and balance training.
For people at genuinely high risk, the picture is less clear. Trials in older adults in residential care, those with osteoporosis, severe vitamin D deficiency, or very low dietary calcium intake have shown some benefit, and most clinical guidelines still recommend supplementation alongside osteoporosis medications. The BMJ authors explicitly note their findings "may not be generalisable to individuals with specific bone disorders or to those receiving drug treatment for osteoporosis."
If you do choose to supplement, the form matters more than the dose. A 1,200 mg dose of poorly absorbed calcium carbonate is not equivalent to a smaller dose of a more bioavailable form. Look for transparency about the calcium source, human absorption studies (not just animal data), and clear tolerability information, particularly around the gastrointestinal side effects that the BMJ paper specifically called out as a real-world problem.
Talk to your GP or pharmacist if you're already supplementing. The review does not suggest stopping calcium is dangerous, but it does suggest the benefit may be smaller than many people have been led to believe, and the tolerability and cardiovascular questions are worth a conversation.
FINAL THOUGHTS
The Bigger Picture
What the 2026 BMJ meta-analysis really shows is that we have spent thirty years studying a fairly narrow version of "calcium supplementation" — mostly calcium carbonate and calcium citrate, at standard doses, in mixed populations — and the results have been underwhelming. The authors are right to call for clinical guidelines and regulatory agencies to revisit their general recommendations.
What the study does not show is that calcium itself is unimportant, or that all calcium sources behave identically in the human body. Those are different questions, and they deserve their own trials.
For now, the most defensible position is the one the BMJ authors themselves take: routine supplementation isn't the answer for most people, food and exercise remain the foundation, and the next generation of research needs to look more carefully at how nutrients are delivered — not just whether they're swallowed.
Frequently Asked Questions
Calcium, Absorption, and the BMJ Review
The 2026 BMJ systematic review by Massé and colleagues pooled 69 randomised controlled trials involving 153,902 participants. It found that calcium supplementation alone, vitamin D supplementation alone, and combined calcium-plus-vitamin-D supplementation each showed little to no clinically meaningful benefit for preventing fractures or falls, based on moderate-to-high certainty evidence.
No. The review applied no restrictions on the type or dose of calcium and did not separately analyse different calcium forms. The included trials predominantly used conventional calcium salt forms such as calcium carbonate and calcium citrate. Newer or more bioavailable forms, including ionic calcium, were not specifically evaluated.
No. The review did not assess participants' digestive capacity, including stomach acid production, which is known to decline with age and directly affects how well calcium salts are absorbed. Many older adults also take acid-suppressing medications such as proton pump inhibitors that further reduce calcium absorption from conventional supplements.
The study does not suggest stopping calcium is dangerous, but it does indicate that routine supplementation in generally healthy adults provides less benefit than previously assumed. The findings may not apply to people with osteoporosis, severe vitamin D deficiency, those in residential care, or anyone taking osteoporosis medication. Anyone currently supplementing should speak with their GP or pharmacist before making changes.
Calcium carbonate, the most studied form, requires stomach acid to dissociate and adequate vitamin D status for active transport across the intestinal wall. Ionic calcium is already in its dissociated form (Ca²⁺), and absorption studies suggest it can use passive paracellular pathways that are less dependent on vitamin D status. No large randomised trial has yet directly compared fracture outcomes across different calcium forms.
The study reinforces that pills alone are not the foundation of bone health. Dietary calcium from food sources (dairy, leafy greens, sardines, fortified plant milks), adequate sunlight or vitamin D from diet, resistance and balance exercise, and not smoking remain the strongest evidence-based interventions for maintaining bone strength and reducing fracture risk across a lifetime.
Disclaimer
This article is general information about published research and is not medical advice. If you have questions about calcium supplementation, speak with your GP, pharmacist, or accredited dietitian.
Reference
Massé O, Mercurio CM, Dupuis S, Al Sahwi M, Arruda A, Dallaire G, Desforges K, Dugré N, Williamson D. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. BMJ 2026; 393: e088050. doi:10.1136/bmj-2025-088050.