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Research · Supplements

Calcium

Calcium supplements raised bone density 0.7 to 1.8% in adults over 50, a gain that did not grow over time. A 2026 meta-analysis of 69 trials found little to no effect on fractures. A 2025 Cochrane update found little to no difference in preeclampsia, unlike earlier reviews. Kidney stones rose 17% in the WHI trial. Heart attack findings disagree.

Add to Bio HackChecked 2026-11-13
Status
Dietary supplement in the US. Calcium carbonate is also sold as an over-the-counter antacid.
Also called
calcium carbonate, calcium citrate, calcium supplements, calcium with vitamin D, coral calcium, bone meal, dolomite, oyster shell calcium, Tums
Taken for
bone density, preventing fractures, osteoporosis, pregnancy, preeclampsia, teeth, muscle function, PMS, period pain

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help4

Reported risks5

What people take it for, and what was found

Shown to help4

Moderate

Bone mineral density

Shown to raise bone density by 0.7% to 1.8% in people over 50, a gain the authors judged unlikely to meaningfully cut fractures.

The numbers and sources
Effect
Calcium supplements raised bone density by 0.7 to 1.8% at five skeletal sites. The gain at later time points was similar to the gain at one year. Calcium from food raised it by similar amounts at most sites [6]. Hip density was 1.06% higher with calcium plus vitamin D than placebo in postmenopausal women [7]. In postmenopausal women with osteoporosis, calcium plus vitamin D raised pelvic density slightly (SMD 0.20, 95% CI 0.05 to 0.35), with no significant change at the lumbar spine, femoral neck or total hip [2].
Population
59 RCTs in people over 50, 51 of them of supplements (12,257 people) [6]; 36,282 postmenopausal women aged 50 to 79 [7]; 11 RCTs in women with osteoporosis [2].
Sources
[6], [7], [2]
Caveats
The review authors write that gains of this size are unlikely to lead to a clinically meaningful drop in fractures [6].
Limited

Tooth loss and cavities

Limited evidence: secondary analyses found fewer older adults lost teeth on calcium with vitamin D, and fewer children had cavities when mothers took calcium in pregnancy.

The numbers and sources
Effect
In 145 adults aged 65 and older who finished a 3-year trial of calcium with vitamin D against placebo for bone loss, 13% (11 of 82) on supplements and 27% (17 of 63) on placebo lost one or more teeth during the trial (OR 0.4, 95% CI 0.2 to 0.9) [12]. Among 195 children aged 12 whose mothers took calcium or placebo in pregnancy, 63.3% in the calcium group and 86.6% in the placebo group had at least one decayed, missing or filled tooth (RR 0.73, 95% CI 0.62 to 0.87) [13].
Population
Healthy adults aged 65 and older [12]. A random sample of children from a trial of 614 pregnant women at one hospital in Rosario, Argentina [13].
Sources
[12], [13]
Caveats
Both are secondary analyses of trials designed for other outcomes. The older adults took calcium together with vitamin D, so calcium alone was not tested [12]. Only 195 of the trial's children were examined [13].
ModerateStudied in women

PMS symptoms

Shown in several trials to ease PMS symptoms more than placebo. In the largest, total symptom scores fell 48% on calcium and 30% on placebo.

Compared with placebo [21][22]; placebo or usual diet across the trials reviewed [23]

The numbers and sources
Effect
In a trial of 1,200 mg of calcium a day as carbonate for 3 cycles, luteal phase symptom scores were lower than on placebo in the second (P = .007) and third (P < .001) cycles. By the third cycle, total symptom scores had fallen 48% from baseline on calcium and 30% on placebo, and all 4 symptom groups (negative mood, water retention, food cravings, pain) were lower [21]. In college students, 500 mg twice a day for 3 months improved early tiredness, appetite changes and depressive symptoms more than placebo [22]. A review of 31 RCTs found that all 4 calcium trials (776 women) reported benefits on PMS symptoms, including a crossover trial of 2,000 mg a day and a trial of calcium-rich food against usual diet [23].
Population
466 women aged 18 to 45 with moderate to severe PMS at 12 US centers [21]; female college students with PMS, mean age 21.4 [22]; 4 trials with 776 women within a review of 31 RCTs [23].
Sources
[21], [22], [23]
Caveats
Only 1 of the 31 trials in the review had a low risk of bias [23]. Trials lasted 2 to 3 cycles.
LimitedStudied in women

Period pain

One small trial found calcium alone lowered period pain 1.6 points on a 10-point scale more than placebo. Calcium with vitamin D did not differ significantly.

Compared with placebo [24]

The numbers and sources
Effect
Taken from day 15 of the cycle until pain ended in the next cycle, for 3 cycles, 1,000 mg of calcium lowered mean pain intensity by 1.6 points more than placebo (95% CI 0.6 to 2.6). Calcium with 5,000 IU of vitamin D3 lowered it by 0.7 points, which was not significant (95% CI -0.3 to 1.6). Menstrual blood loss did not differ from placebo in either group [24].
Population
85 university students with moderate or severe primary dysmenorrhea in Iran [24].
Sources
[24]
Caveats
One small trial. Time and the interaction of time with group had no significant effect on pain [24].

Mixed results2

Moderate

Fractures

Mixed results: recent reviews found calcium alone did not lower fractures and calcium with vitamin D lowered them only slightly. Older reviews found about 11% to 12% fewer.

The numbers and sources
Effect
Recent meta-analyses found little or no effect, and an older one found fewer fractures. A 2026 meta-analysis of 69 trials (153,902 adults) found calcium alone did not significantly lower the risk of any fracture (RR 0.91, 95% CI 0.81 to 1.01, 11 trials, 9,067 people, moderate certainty). Calcium plus vitamin D lowered it slightly (RR 0.91, 95% CI 0.84 to 0.99, 15 trials, 51,126 people, high certainty), below the authors' threshold for a meaningful absolute effect. Other fracture and fall outcomes showed little to no effect [1]. In postmenopausal women with osteoporosis, calcium plus vitamin D did not lower fracture risk (RR 0.98, 95% CI 0.89 to 1.07, 11 RCTs, 43,869 women) [2]. A 2007 meta-analysis of 17 trials (52,625 people) found 12% fewer fractures with calcium or calcium plus vitamin D (RR 0.88, 95% CI 0.83 to 0.95), 24% fewer where adherence was high [3]. A 2015 review found 11% fewer total fractures (RR 0.89, 95% CI 0.81 to 0.96) and no change in hip fractures (RR 0.95, 95% CI 0.76 to 1.18). In the 4 trials at lowest risk of bias (44,505 people), there was no effect at any site, and the authors found signs of publication bias toward calcium [4]. In community-dwelling adults over 50, calcium did not lower hip fracture (RR 1.53, 95% CI 0.97 to 2.42) or other fractures [5].
Population
Adults not on osteoporosis drugs, 87% living in the community [1]. Postmenopausal women with osteoporosis [2]. Adults aged 50 or older in 17 trials [3], 26 trials [4] and 33 trials with 51,145 people [5].
Sources
[1], [2], [3], [4], [5]
Caveats
The 2015 review found only one trial with a clear fracture reduction, in frail women in residential care with low calcium intake and low vitamin D [4]. Evidence for people in residential care or at high fracture risk was limited in the 2026 review [1].
Moderate

Preeclampsia and high blood pressure in pregnancy

Mixed results: the 2025 Cochrane update found little to no difference in preeclampsia, while the 2018 version and earlier reviews found fewer cases at 1 g a day or more.

The numbers and sources
Effect
Sources disagree. The 2025 Cochrane update found little to no difference in preeclampsia against placebo (RR 0.83, 95% CI 0.67 to 1.04, 6 RCTs, 15,364 women, low certainty). In the 4 trials of 500 or more women (14,730), the RR was 0.92 (95% CI 0.79 to 1.05, high certainty), and preterm birth before 37 weeks did not differ (RR 0.97, 95% CI 0.85 to 1.11). Baseline calcium intake and preeclampsia risk did not change the findings, and low and high doses did not differ (RR 0.96, 2 RCTs, 22,000 women) [8]. The 2018 version of the review found that 1 g a day or more lowered high blood pressure (RR 0.65, 95% CI 0.53 to 0.81) and preeclampsia (RR 0.45, 95% CI 0.31 to 0.65), with a clear effect in women with low calcium diets (RR 0.36), and that preterm birth fell (RR 0.76, 95% CI 0.60 to 0.97) [9]. An umbrella review of earlier meta-analyses reported a pooled RR for preeclampsia of 0.53 (95% CI 0.42 to 0.68, I² 84%) [10]. Calcium started before pregnancy did not change preeclampsia in 1,355 women with prior preeclampsia (RR 0.84, 95% CI 0.62 to 1.14) [11].
Population
10 trials with 37,504 women [8]. 13 trials with 15,730 pregnant women [9]. 1,355 parous women in one trial [11].
Sources
[8], [9], [10], [11]
Caveats
The 2025 update removed 20 previously included trials, 11 because eligibility criteria changed and 9 that await classification over trustworthiness concerns. It was part-funded by WHO [8]. The umbrella review's search ended in December 2023, before those exclusions [10]. Heterogeneity was high in the 2018 review and small-study effects were possible. In its largest trial, preeclampsia fell only 8% and the interval included no effect [9].

Doses studied

The WHI trial used 1,000 mg of elemental calcium as carbonate with 400 IU of vitamin D3 a day [7]. Pregnancy trials used at least 1 g a day [9]. The heart attack meta-analysis included trials of 500 mg a day or more [14]. The 2007 fracture meta-analysis found larger effects at 1,200 mg or more than below it [3]. The levothyroxine study used 1,200 mg a day as carbonate [15]. EFSA sets a tolerable upper intake level of 2,500 mg a day for adults, including during pregnancy [16]. A 2016 review describes US tolerable upper intake levels as 2,000 to 2,500 mg a day [17].

Risks

Reported risks4

LimitedVery common

Reduced levothyroxine absorption

Limited evidence: in 20 adults on levothyroxine, 1,200 mg of calcium carbonate lowered free T4 and raised TSH, which returned after stopping calcium.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
Taking 1,200 mg of calcium as carbonate with levothyroxine for 3 months lowered free T4 from 17 to 15 pmol/L and raised TSH from 1.6 to 2.7 mIU/L. Both returned after calcium stopped. 20% of patients had TSH above the normal range on calcium [15].
Population
20 adults with hypothyroidism on stable levothyroxine [15].
Sources
[15]
Caveats
A small uncontrolled cohort, with lab data showing T4 binds to calcium carbonate in acid [15].
LimitedHow often is not known

Kidney stones

One trial found kidney stones about 17% more common on calcium plus vitamin D than placebo over 7 years in postmenopausal women.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Kidney stones were more common on calcium plus vitamin D than placebo (HR 1.17, 95% CI 1.02 to 1.34) over an average 7.0 years [7].
Population
36,282 postmenopausal women in the Women's Health Initiative [7].
Sources
[7]
Caveats
One trial, of calcium combined with vitamin D.
Why limited
This rests on one trial, of 36,282 people. Strength counts independent studies that agree, so one trial is limited at any size.
LimitedHow often is not known

Prostate cancer

Linked to slightly higher prostate cancer risk in men with higher total, dietary or dairy calcium intake, in cohort studies. Calcium supplements were not significantly linked.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 21 prospective cohorts, supplemental calcium was not significantly associated with prostate cancer. Higher total (effect size 1.08, 95% CI 1.01 to 1.15), dietary (1.16, 95% CI 1.08 to 1.24) and dairy calcium (1.13, 95% CI 1.02 to 1.24) intakes were associated with higher risk [19].
Population
Men in prospective cohort studies [19].
Sources
[19]
Caveats
Observational intake data, not trials. Highest against lowest intake comparisons [19].
LimitedHow often is not known

Lead in calcium supplements

Limited evidence: two-thirds of 136 calcium supplement brands bought in 1996 exceeded California's lead limit, while most refined antacids met it.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Two-thirds of 136 calcium supplement brands bought in 1996 exceeded the 1999 California limit of 1.5 µg of lead per daily calcium dose. Refined antacid products and infant formulas had the lowest lead, and 85% of antacids met the limit [20].
Population
Products, not people: bone meal, dolomite, oyster shell, chelated and refined calcium [20].
Sources
[20]
Caveats
Products bought in 1996. Current product lead levels may differ.

Mixed results1

LimitedHow often is not known

Heart attack and cardiovascular events

Limited evidence: one 2010 review linked calcium without vitamin D to more heart attacks, while later reviews found no change in heart disease.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Sources disagree. A 2010 meta-analysis of calcium without vitamin D found more heart attacks (patient data HR 1.31, 95% CI 1.02 to 1.67; trial data RR 1.27, 95% CI 1.01 to 1.59) [14]. A 2015 meta-analysis of 18 trials in older women found no change in coronary heart disease (RR 1.02, 95% CI 0.96 to 1.09), heart attack (RR 1.08, 95% CI 0.92 to 1.26) or death (RR 0.96) [18]. A 2016 review of 4 trials and 27 observational studies found no consistent link between calcium intake within upper limits and cardiovascular disease [17].
Population
15 trials of people with a mean age over 40, 8,151 with patient-level data and 11,921 with trial-level data [14]; 63,563 women [18]; generally healthy adults [17].
Sources
[14], [18], [17]
Caveats
Cardiovascular outcomes were secondary end points in all the trials [17]. The 2016 review was funded by the National Osteoporosis Foundation [17].

Claims tested and not found

  1. That calcium supplements prevent hip fractures. Hip fracture did not fall in pooled trials [4][5].
  2. That calcium supplements alone lower fracture risk. Any fracture did not fall significantly across 11 trials of calcium alone [1].
  3. That calcium in pregnancy prevents preeclampsia in large trials. In 4 trials of 500 or more women, preeclampsia did not differ from placebo [8].
  4. That more dietary calcium prevents fractures. Cohort studies mostly found no link between dietary calcium and fracture, and no trial showed that calcium from food prevents fractures [4].

Sources

  1. Massé O, Mercurio CM, Dupuis S, et al. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. BMJ. 2026. https://doi.org/10.1136/bmj-2025-088050
  2. Cong B, Zhang H. The effects of combined calcium and vitamin D supplementation on bone mineral density and fracture risk in postmenopausal women with osteoporosis: a systematic review and meta-analysis of randomized controlled trials. BMC Musculoskeletal Disorders. 2025. https://doi.org/10.1186/s12891-025-09089-7
  3. Tang BM, Eslick GD, Nowson C, et al. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. The Lancet. 2007. https://doi.org/10.1016/S0140-6736(07)61342-7
  4. Bolland MJ, Leung W, Tai V, et al. Calcium intake and risk of fracture: systematic review. BMJ. 2015. https://doi.org/10.1136/bmj.h4580
  5. Zhao JG, Zeng XT, Wang J, et al. Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults. JAMA. 2017. https://doi.org/10.1001/jama.2017.19344
  6. Tai V, Leung W, Grey A, et al. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ. 2015. https://doi.org/10.1136/bmj.h4183
  7. Jackson RD, LaCroix AZ, Gass M, et al. Calcium plus Vitamin D Supplementation and the Risk of Fractures. New England Journal of Medicine. 2006. https://doi.org/10.1056/NEJMoa055218
  8. Cluver CA, Rohwer C, Rohwer AC. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database of Systematic Reviews. 2025. https://doi.org/10.1002/14651858.CD001059.pub6
  9. Hofmeyr GJ, Lawrie TA, Atallah ÁN, et al. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database of Systematic Reviews. 2018. https://doi.org/10.1002/14651858.CD001059.pub5
  10. Kumsa H, Mislu E, Arage MW, et al. Effects of calcium supplementation on the prevention of preeclampsia: an umbrella review of systematic reviews and meta-analyses. Frontiers in Medicine. 2025. https://doi.org/10.3389/fmed.2025.1434416
  11. Cluver CA, Rohwer C, Rohwer A, et al. Calcium supplementation commenced before pregnancy for preventing hypertensive disorders and related problems. Cochrane Database of Systematic Reviews. 2025. https://doi.org/10.1002/14651858.CD011192.pub4
  12. Krall EA, Wehler C, Garcia RI, et al. Calcium and vitamin D supplements reduce tooth loss in the elderly. American Journal of Medicine. 2001. https://doi.org/10.1016/s0002-9343(01)00899-3
  13. Bergel E, Gibbons L, Rasines MG, et al. Maternal calcium supplementation during pregnancy and dental caries of children at 12 years of age: follow-up of a randomized controlled trial. Acta Obstetricia et Gynecologica Scandinavica. 2010. https://doi.org/10.3109/00016349.2010.518228
  14. Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010. https://doi.org/10.1136/bmj.c3691
  15. Singh N, Singh PN, Hershman JM. Effect of Calcium Carbonate on the Absorption of Levothyroxine. JAMA. 2000. https://doi.org/10.1001/jama.283.21.2822
  16. European Food Safety Authority. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Version 11. 2025. https://www.efsa.europa.eu/sites/default/files/assets/UL_Summary_tables.pdf
  17. Chung M, Tang AM, Fu Z, et al. Calcium Intake and Cardiovascular Disease Risk. Annals of Internal Medicine. 2016. https://doi.org/10.7326/M16-1165
  18. Lewis JR, Radavelli-Bagatini S, Rejnmark L, et al. The Effects of Calcium Supplementation on Verified Coronary Heart Disease Hospitalization and Death in Postmenopausal Women: A Collaborative Meta-Analysis of Randomized Controlled Trials. Journal of Bone and Mineral Research. 2015. https://doi.org/10.1002/jbmr.2311
  19. Xiong K, Lu L, Ge P, et al. Calcium intake and risk of prostate cancer: A systematic review and dose-response meta-analysis of prospective cohort studies. Journal of Trace Elements in Medicine and Biology. 2025. https://doi.org/10.1016/j.jtemb.2025.127652
  20. Scelfo GM, Flegal AR. Lead in calcium supplements. Environmental Health Perspectives. 2000. https://doi.org/10.1289/ehp.00108309
  21. Thys-Jacobs S, Starkey P, Bernstein D, Tian J. Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. American Journal of Obstetrics and Gynecology. 1998. https://doi.org/10.1016/s0002-9378(98)70377-1
  22. Ghanbari Z, Haghollahi F, Shariat M, et al. Effects of calcium supplement therapy in women with premenstrual syndrome. Taiwanese Journal of Obstetrics and Gynecology. 2009. https://doi.org/10.1016/s1028-4559(09)60271-0
  23. Robinson J, Ferreira A, Iacovou M, Kellow NJ. Effect of nutritional interventions on the psychological symptoms of premenstrual syndrome in women of reproductive age: a systematic review of randomized controlled trials. Nutrition Reviews. 2025. https://doi.org/10.1093/nutrit/nuae043
  24. Zarei S, Mohammad-Alizadeh-Charandabi S, Mirghafourvand M, et al. Effects of calcium-vitamin D and calcium-alone on pain intensity and menstrual blood loss in women with primary dysmenorrhea: a randomized controlled trial. Pain Medicine. 2017. https://doi.org/10.1093/pm/pnw121

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