What is the appropriate calcium carbonate dosing regimen for an older adult requiring calcium supplementation (target elemental calcium 1000‑1200 mg per day), including tablet strength, frequency, and safety considerations?

Calcium Carbonate Dosing for Geriatric Patients

For older adults requiring calcium supplementation, prescribe calcium carbonate 500 mg tablets (providing 200 mg elemental calcium per tablet) taken 2-3 times daily with meals to achieve the target of 1000-1200 mg elemental calcium per day, accounting for dietary intake. 1

Target Daily Intake

• Women over 50 years and men over 70 years require 1200 mg elemental calcium per day from all sources (diet plus supplements). 1
• Men aged 50-70 years require 1000 mg per day. 1
• Never exceed 2000 mg total daily calcium intake (from all sources) in adults over 50 years, as this is the upper safety limit. 1

Practical Dosing Regimen

Calcium carbonate provides 40% elemental calcium by weight, meaning a 500 mg calcium carbonate tablet delivers approximately 200 mg of elemental calcium. 1, 2

Dosing Algorithm:

1. Assess current dietary calcium intake first (dairy products, fortified foods). 1
2. Calculate supplementation need: If dietary intake is 400-600 mg/day, supplement with 600-800 mg elemental calcium (requiring 3-4 tablets of 500 mg calcium carbonate). 1
3. Divide doses throughout the day: Maximum 500 mg elemental calcium per dose (approximately 2-3 tablets of calcium carbonate per dose) to optimize absorption. 3, 2
4. Typical regimen: One to two 500 mg calcium carbonate tablets taken 2-3 times daily with meals. 1

Critical Administration Instructions

Calcium carbonate MUST be taken with meals because it requires gastric acid for optimal absorption. 1, 2 This is the most common pitfall—taking it on an empty stomach dramatically reduces bioavailability. 2

• Timing: Administer with breakfast, lunch, and dinner to maximize absorption and minimize gastrointestinal side effects. 3, 2
• Spacing: Dividing doses into 2-3 administrations throughout the day significantly improves total calcium absorption compared to single daily dosing. 3, 4

Special Considerations for Geriatric Patients

Patients on acid-suppressing medications (proton pump inhibitors, H2-blockers) should use calcium citrate instead of calcium carbonate, as carbonate absorption is severely impaired in low-acid environments. 2, 5

• Calcium citrate does not require gastric acid and can be taken without food, though it provides only 21% elemental calcium (requiring larger or more frequent doses). 1, 5
• Calcium citrate also causes less gastrointestinal irritation in patients with sensitive stomachs. 5

Safety Profile and Common Pitfalls

Constipation and bloating are the most common side effects of calcium carbonate supplementation. 1

Nephrolithiasis (kidney stones) risk increases modestly with calcium supplements (but not dietary calcium), with approximately 1 additional kidney stone per 273 women supplemented over 7 years. 3

Cardiovascular risk concerns have been raised in recent studies regarding calcium supplementation, though evidence remains inconsistent and inconclusive. 1, 3 Patients should be informed of this potential risk, particularly if they have existing cardiovascular disease.

Key Pitfalls to Avoid:

• Do not exceed 2000 mg total daily intake from all sources in geriatric patients. 1
• Do not prescribe calcium carbonate to patients on chronic acid suppression without switching to calcium citrate. 2, 5
• Do not give single large doses—absorption efficiency decreases significantly with doses exceeding 500 mg elemental calcium. 3, 2
• Do not rely solely on supplements—dietary calcium from food sources is preferred and should be maximized first. 1

Cost-Effectiveness

Calcium carbonate is the least expensive and most commonly used supplement, making it the preferred first-line option when taken appropriately with meals. 1, 2