Closing the Calcium Gap: How Pharmacists Can Guide Patients Toward Better Bone Health

Bone health is critical to overall health because the adult skeletal system, which contains 206 bones, provides the body’s framework, facilitates movement, protects vital organs, and anchors muscles.¹ Its tissues play an important role in regulating mineral and acid-base balance homeostasis and also provide the environment for hematopoiesis within the bone marrow.¹

As the most abundant mineral in the body, calcium is a major component of bones. The National Institutes of Health (NIH) Office of Dietary Supplements indicates that it is found naturally in some foods, added to others, present in some medicines (such as antacids), and available as a dietary supplement.²

Some individuals try to obtain adequate amounts of calcium through diet, and some elect to use calcium supplements to ensure they meet the recommended daily amounts; however, many do not meet their daily needs. The literature indicates that inadequate calcium intake is common among US adults.^2-4

According to data from the National Health and Nutrition Examination Survey, an estimated 42% to 50% of Americans fail to reach their estimated average requirements for calcium.^2-4 Some sources also indicate that although clinical hypocalcemia is rare, suboptimal calcium intake is a common issue that may lead to bone loss over time.⁴

Age-related bone loss or prolonged calcium deficiency can lead to osteoporosis and an increased risk of bone fractures.² The FDA has approved a health claim for products containing calcium and vitamin D, affirming that they can reduce the risk of osteoporosis in older adults, a population in which bone health is particularly important.² According to a CDC report, 19.2% of adults aged 60 and older use calcium supplements, making it the fourth most commonly used supplement in this age group.⁵ Another report indicates that an estimated 70% of older women take supplements that contain calcium, whereas men generally obtain calcium through diet.⁶

OTC Calcium Supplements

Oral calcium supplements are approved for use in the treatment and prevention of calcium deficiency. Other FDA-approved uses include treatment of acid indigestion and hyperphosphatemia associated with end-stage renal disease.⁷

Calcium carbonate and calcium citrate are the 2 most common forms of calcium found in supplements. Calcium carbonate contains 40% elemental calcium, whereas calcium citrate contains 21% elemental calcium.⁷ Other forms of calcium supplements include calcium lactate, calcium gluconate, and calcium phosphate. Calcium supplements are formulated as single-entity products or in combination with vitamin D in various dosage forms, including tablets, caplets, chewable tablets, soft chews, and gummies, and are also commonly found in multivitamin/multimineral supplements.⁷ The 2026 Pharmacy Times OTC Guide indicates that the 3 most common pharmacist recommendations for calcium-containing supplements are Citracal, Caltrate, and those by Nature Made.⁸

Key Patient Counseling Tips

Pharmacists are uniquely positioned to identify potential contraindications and drug interactions involving calcium supplements, make appropriate clinical recommendations, and counsel patients on safe and proper use.

Patients should be encouraged to discuss their individual needs with their primary health care provider. Helpful resources on recommended calcium intake by age for pediatric and adult populations are available on the websites of the American Academy of Pediatrics and the International Osteoporosis Foundation. The Table^9,10 provides several main counseling points that pharmacists can give patients.

Key counseling tips include the following^2,7:

• Elevated urinary calcium and renal stones can arise from excess intake.
• Hypercalcemia symptoms include anorexia, nausea, vomiting, constipation, and polyuria, especially in individuals taking high-dose vitamin D formulations.
• Calcium carbonate and calcium phosphate should be taken with food to optimize absorption, whereas calcium citrate may be taken with or without food and is preferred for patients with reduced stomach acid, such as those with achlorhydria or who are on chronic therapy with proton pump inhibitors or histamine-2 (H2) blockers.
• Calcium absorption is greatest when taken in doses of 500 mg or less once daily. Patients requiring 1000 mg/day or more should divide doses throughout the day rather than taking all at once to maximize absorption.

Drug Interactions

Because some pharmacologic agents can inhibit or decrease calcium absorption, patients should discuss calcium supplementation with their primary health care provider to determine whether it is appropriate.⁷ Calcium can interfere with or reduce the absorption of bisphosphonates, so patients should wait at least 30 minutes before taking calcium supplements after taking risedronate, alendronate, or alendronate/cholecalciferol and at least 60 minutes after taking ibandronate.^2,7 Examples of other medications that should be administered in separate dosing intervals (at least 2 hours apart) when used in conjunction with calcium supplements include antacids containing aluminum and antibiotics such as tetracyclines and fluoroquinolones.^2,7

Patients taking proton pump inhibitors or H2 receptor antagonists, which reduce gastric acid, may have decreased absorption of calcium carbonate. Switching to calcium citrate, which does not depend on gastric acid for absorption, may be appropriate in these patients.⁷

Conclusion

Pharmacists can be a valuable resource for patients seeking guidance on selecting and using calcium supplements and can encourage patients to seek further medical evaluation when warranted to ensure appropriateness. Additionally, pharmacists can play a key role in identifying patients at elevated risk of bone loss, osteopenia, or osteoporosis due to underlying medical conditions or certain medications. Patient education should also include guidance on the risks associated with excessive calcium intake to ensure safe and appropriate use.

REFERENCES

1. Kamel-El Sayed SA, Nezwek TA, Varacallo MA. Physiology, Bone. In: StatPearls. StatPearls Publishing; 2026-. Updated September 10, 2024. Accessed July 8, 2026. https://www.ncbi.nlm.nih.gov/books/NBK441968/

2. Calcium: Fact sheet for health professionals. National Institutes of Health Office of Dietary Supplements. Updated June 22, 2026. Accessed July 8, 2026. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/

3. Yu Z, Li Y, Ba DM, et al. Trends in calcium intake among the US population: results from the NHANES (1999-2018). Nutrients. 2024;16(5):726. doi:10.3390/nu16050726

4. Shlisky J, Mandlik R, Askari S, et al. Calcium deficiency worldwide: prevalence of inadequate intakes and associated health outcomes. Ann N Y Acad Sci. 2022;1512(1):10-28. doi:10.1111/nyas.14758

5. Mishra S, Stierman B, Gahche JJ, Potischman N. Dietary supplement use among adults: United States, 2017-2018. NCHS Data Brief. 2021;(399):1-8. doi:10.15620/cdc:101131

6. Drake MT, Bockman RS. Calcium supplements, vitamin D, and osteoporosis. Hospital for Special Surgery. Updated September 12, 2025. Accessed July 8, 2026. https://www.hss.edu/health-library/conditions-and-treatments/calcium-supplements-vitamind-osteoporosis

7. Bridgeman MB, Rollins CJ. Essential and conditionally essential nutrients. In: Krinsky DL, Ferreri SP, Hemstreet B, et al. Handbook of Nonprescription Drugs: An Interactive Approach to Self-Care. 21st ed. American Pharmacists Association; 2024:437-438.

8. Calcium supplements. Pharmacy Times OTC Guide. Accessed July 8, 2026. https://www.pharmacytimes.com/otcguide/vitamins-and-dietary-supplements/calcium-supplements

9. LeBoff MS, Greenspan SL, Insogna KL, et al. The clinician’s guide to prevention and treatment of osteoporosis. Osteoporos Int. 2022;33(10):2049-2102. doi:10.1007/s00198-021-05900-y

10. Prevention. International Osteoporosis Foundation. Accessed July 8, 2026. https://www.osteoporosis.foundation/patients/prevention