Calcium is the most abundant mineral in your body, and your bones and teeth depend on it. Human studies agree that you need enough of it. They do not agree that adding supplements helps most people: a 2026 BMJ review of 69 trials found little to no fracture or fall protection from calcium, vitamin D, or both, in mostly community-dwelling adults not at high risk. Studies of bone density, cancer, and heart health are smaller, mixed, or based on observation only.
Quick facts
| Topic | What the sources report |
|---|---|
| Forms | Most supplements use calcium carbonate or calcium citrate. Others include sulfate, ascorbate, microcrystalline hydroxyapatite, gluconate, lactate, and phosphate (NIH Office of Dietary Supplements). |
| Doses used in studies | About 500 to 2,000 mg a day of elemental calcium, often paired with 400 to 2,000 IU of vitamin D3. Food-based trials used milk or dairy. |
| Typical study length | Mostly 1 to 7 years for fracture and cancer trials. Weight-loss trials ran at least 6 months. |
| Main studied uses | Fracture and fall prevention, bone mineral density, colorectal and other cancers, heart disease, metabolic syndrome, weight, pregnancy, and low calcium after thyroid surgery. |
| Strength of evidence | Strongest for needing calcium to build and keep bone. Weak or mixed for most disease-prevention uses. |
What do human studies show?
Fractures and falls
This is the best-studied use, and the large reviews lean against benefit. The 2026 BMJ systematic review and meta-analysis pooled 69 randomized trials with 153,902 adults. For any fracture, calcium alone had a risk ratio of 0.91 (95% CI 0.81 to 1.01, 11 trials, 9,067 people, moderate certainty). That range includes no effect. Vitamin D alone had a risk ratio of 1.00. Calcium plus vitamin D had 0.91 (0.84 to 0.99, 15 trials, 51,126 people). The authors judged these effects too small to be clinically meaningful. Evidence for people at high fracture risk or in residential care was limited.
Other pooled analyses disagree. According to the NIH fact sheet, a meta-analysis of eight trials in 30,970 adults over 50 found that calcium (500 to 1,200 mg a day) plus vitamin D (400 to 800 IU) for 1 to 7 years cut total fractures by 15% and hip fractures by 30%. A JAMA meta-analysis and a review for the US Preventive Services Task Force found no effect on total fractures. The task force concluded with moderate certainty that under 1,000 mg of calcium with under 400 IU of vitamin D does not prevent fractures in postmenopausal women. It found the evidence on larger doses inadequate, and also inadequate for men and premenopausal women.
One trial points a different way. A nutrition-education write-up describes a cluster-randomized trial in 60 Australian care homes where residents ate under about 600 mg of calcium a day. Homes that raised dairy servings reached about 1,142 mg of calcium and 1.1 g/kg of protein a day. Over about 12.6 months, fracture risk was 33% lower (HR 0.67) and hip fracture risk 46% lower (HR 0.54). The residents averaged 86 years old with many health conditions, and the diet change raised protein as well as calcium. It may not apply to healthier or younger people.
Bone mineral density
Bone density is a measurement, and a better number does not always mean fewer breaks. Our guide to surrogate outcomes explains why. A 2015 BMJ analysis found that raising calcium intake from food or supplements in people over 50 gave small 1 to 2% density gains. The authors considered these unlikely to reduce fractures meaningfully.
The NIH fact sheet reports that a meta-analysis of 15 trials in 78,206 postmenopausal women found calcium plus vitamin D raised total, lumbar spine, arm, and femoral neck density, though calcium alone had no effect on the femoral neck. A 2-year trial in 500 postmenopausal women gave milk enriched to provide 900 mg calcium and 600 IU vitamin D and found higher femoral neck density. In the Women’s Health Initiative trial (1,000 mg calcium plus 400 IU vitamin D3, 36,282 women), height loss was no different from placebo. Observational studies on calcium intake and density are mixed.
A 2025 meta-analysis of 13 trials in postmenopausal women compared exercise plus calcium and vitamin D with calcium and vitamin D alone. Adding exercise raised lumbar spine and femoral neck density further. Whole-body vibration and mind-body exercise showed the most benefit, and short programs (6 months or less) did better than longer ones. This tells you about exercise, not about calcium by itself.
Colorectal and other cancers
Observational studies often link higher calcium intake to lower colorectal cancer risk. One meta-analysis found risk dropped 8% per 300 mg a day. Trials are mixed: the Women’s Health Initiative follow-up found no difference in colorectal cancer, and one trial found no effect on recurring adenomas. A meta-analysis of four trials using 1,200 to 2,000 mg a day for 36 to 60 months found an 11% lower chance of recurrent adenomas but no effect on advanced adenomas. For all cancers combined, most trials found no benefit, and the NIH fact sheet notes that scientists questioned one positive trial because it was not designed to measure cancer.
A 2026 meta-analysis of 14 cohort studies found higher calcium intake linked to 7% lower breast cancer risk (RR 0.93). The link held for dietary calcium, not for supplements alone, and the authors say it does not prove cause. Some observational studies link high dairy calcium to higher prostate cancer risk. Calcium from non-dairy foods and supplements was not clearly linked. Overall, the NIH fact sheet says more well-designed trials are needed.
Heart disease and metabolic syndrome
The NIH fact sheet says large observational studies tie lower calcium intake to higher risk of hypertension, stroke, and atherosclerosis. It also says some cohort studies and trials found calcium supplements might raise cardiovascular risk, while others found no link. The picture is unsettled. A 2026 meta-analysis of 24 cross-sectional studies found higher dietary calcium linked to 15% lower odds of metabolic syndrome (OR 0.85). These studies capture one moment in time, so they cannot show that calcium caused the difference.
Weight, pregnancy, and after thyroid surgery
An overview of systematic reviews found that 1,000 mg a day for at least 6 months led to weight loss in overweight and obese non-pregnant women compared with placebo. It found no effect on weight gain in pregnancy (1,000 to 2,000 mg a day) and too little data on bone density. The same overview cites WHO guidance recommending 1.5 to 2.0 g a day of calcium for pregnant women with low dietary intake to reduce pre-eclampsia risk, and notes WHO linked supplementation to a higher risk of HELLP syndrome.
After total thyroidectomy, low blood calcium is common. A 2026 network meta-analysis of 20 trials (3,669 patients) found calcium plus vitamin D reduced clinical hypocalcaemia versus no supplementation (OR 0.31). Calcium alone showed no significant benefit. This is a surgical setting managed by the surgical team.
Why do people say calcium is no longer recommended?
Because the supplement question has changed, not the nutrient question. Official intake targets still exist. The NIH fact sheet lists 1,000 to 1,200 mg a day for adults. But the 2015 BMJ analyses and the 2026 BMJ review found that extra calcium, from food or pills, does little to prevent fractures in most older adults. The task force reached similar conclusions for under-1,000 mg doses. A commenter group on the draft task force statement (National Center for Health Research) noted the conclusions may not apply to frail people, those in institutions, or those likely to be low in calcium or vitamin D.
Should a 70-year-old take calcium, and which form?
Whether a supplement helps you depends on how much calcium you already eat, your bone health, and your medicines. That is a conversation for a clinician, not something these studies settle. The NIH fact sheet gives 1,200 mg a day as the reference intake for adults over 70, and the trial-based evidence above suggests food and supplements alike add little for fracture prevention in healthy community-dwelling people. The care-home trial suggests people with very low intakes may gain more.
On forms, no study here ranks one as best for seniors. The NIH fact sheet says calcium carbonate absorbs better with food and may cause more gas, bloating, and constipation, especially in older adults with less stomach acid. Calcium citrate is less dependent on stomach acid and can be taken without food, and MedlinePlus notes it costs more.
Doses researchers used
These are amounts from studies, not advice.
| Study or use | Calcium | Length |
|---|---|---|
| Women’s Health Initiative (with 400 IU vitamin D3) | 1,000 mg | About 7 years, then long-term follow-up |
| Fracture meta-analysis (with 400 to 800 IU vitamin D) | 500 to 1,200 mg | 1 to 7 years |
| Enriched milk trial | 900 mg from milk (with 600 IU vitamin D) | 2 years |
| Nebraska cancer trials | 1,400 to 1,500 mg (with or without vitamin D) | 4 years |
| Adenoma meta-analysis | 1,200 to 2,000 mg | 36 to 60 months |
| Weight-loss trials | 1,000 mg | At least 6 months |
| Care-home food trial | About 1,142 mg total from diet | About 12.6 months |
The NIH fact sheet adds that absorption drops as the amount per dose rises. The body absorbs about 36% of a 300 mg dose and 28% of a 1,000 mg dose, and absorption from supplements is highest at doses of 500 mg or less. MedlinePlus likewise says absorption is best at no more than 500 mg at a time. The reference intakes (RDA) for adults are 1,000 to 1,200 mg a day, according to the NIH, and MedlinePlus says 2,500 mg a day appears safe for adults 19 to 50 and 2,000 mg for adults over 50.
Safety, side effects, and interactions
| Issue | What the sources say |
|---|---|
| Stomach effects | Gas, bloating, and constipation. More common with carbonate than citrate. Smaller, more frequent doses or taking it with meals may help. |
| Kidney stones | MedlinePlus says high amounts over a long time raise the risk in some people. The National Center for Health Research comment cites a risk ratio of 1.11 from the task force review. |
| Heart risk | Some studies suggest supplements may raise risk; others find no link. Unresolved. |
| Absorption | Low vitamin D lowers absorption. Caffeine and phosphorus reduce it slightly. Oxalic acid in spinach and rhubarb binds calcium. |
| Medicines | MedlinePlus says some medicines can affect calcium absorption, and your provider can say whether supplements interact with yours. The NIH lists bisphosphonates, cisplatin, and proton pump inhibitors as medicines that can lower blood calcium. |
Calcium is also found in some antacids, at about 270 to 400 mg per chew according to the NIH fact sheet, so count those if you use them.
Who should talk to a clinician first?
- Anyone taking prescription medicines, especially for osteoporosis, cancer, or acid reflux. Calcium products and your medicines can interact.
- People with a history of kidney stones.
- Postmenopausal women and anyone told they have low bone density. The NIH fact sheet says about 30% of postmenopausal women in the US and Europe have osteoporosis. Treatment decisions belong with your clinician.
- People who are pregnant or breastfeeding.
- People who avoid dairy, including those with lactose intolerance or milk allergy, who may need a plan for getting enough.
- Anyone who has had thyroid surgery.
- Anyone considering stopping or changing a bone medicine. These studies do not compare calcium with such drugs in a way that supports swapping one for the other.
Can you get enough from food?
The NIH and MedlinePlus both point to dairy, canned fish with bones, some greens like kale and broccoli, and calcium-fortified foods such as juices, soy milk, tofu, and cereals. Absorption differs: about 27% from milk versus 5% from spinach. Per the NIH fact sheet, a cup of plain low-fat yogurt has about 415 mg and a cup of nonfat milk about 299 mg. MedlinePlus says leafy greens alone are not an adequate source.
What is still unknown?
- Whether the small bone density gains from calcium translate to fewer fractures in anyone beyond very low-intake or institutionalized people.
- Whether calcium supplements affect heart risk.
- Whether calcium lowers cancer risk, given that observational and trial results differ.
- Whether food calcium and supplement calcium work differently.
These studies do not address which country has the highest osteoporosis rates, what is prescribed in Japan, or which newer drugs rebuild bone. They also do not show any single vitamin that rebuilds bone density. Vitamin D helps you absorb calcium, and that is the role the sources describe. For treatment options, a clinician or a national osteoporosis organization is the right source. Our guides to meta-analyses and systematic reviews and ingredient evidence versus marketing claims can help you weigh what you read.
How to read a label that lists calcium
- Amount: The Supplement Facts panel lists elemental calcium. That is the number to use; you do not need to calculate it from the form. The NIH fact sheet says calcium carbonate is 40% calcium by weight and citrate 21%.
- Per serving: Check how many tablets make a serving. Common supplement amounts are 500 or 600 mg, and multivitamins usually carry 200 to 300 mg.
- Form: Carbonate works best with food. Citrate can be taken either way.
- Vitamin D: Many products add it. Check the amount if you are also taking vitamin D separately.
- Blends: If a blend lists only a combined weight without a calcium amount, you cannot tell how much calcium you are getting. The maker’s support team can tell you.
Before you order
- How much calcium do you already get from food and antacids?
- Which medicines do you take, and does your clinician or pharmacist see an interaction?
- Does the label show elemental calcium per serving and the form?
By ClinicalStudyConnect.com Research Desk
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.