From the Guidelines
For oyster shell dosing, I recommend taking 500-1250 mg of calcium carbonate (from oyster shells) once or twice daily, providing 200-500 mg of elemental calcium per dose, as it is the most commonly used supplement and should be taken with meals to improve absorption 1. The total daily calcium intake from all sources should not exceed 2,000-2,500 mg, as intake above 2500 mg per day should be avoided 1.
Key Considerations
- Oyster shell calcium supplements are best absorbed when taken in divided doses rather than all at once, as the body can only absorb about 500 mg of calcium at one time.
- These supplements work by providing calcium carbonate, which neutralizes stomach acid and releases calcium ions that can be absorbed in the small intestine.
- Calcium is essential for bone health, muscle function, nerve transmission, and blood clotting.
- People with kidney stones, hypercalcemia, or certain medical conditions should consult a healthcare provider before taking oyster shell supplements.
- For those with low stomach acid or taking certain medications, calcium citrate might be a better option as it doesn't require stomach acid for absorption.
Important Notes
- The recommended dietary intake of calcium for women 19 to 50 years of age and men 19 to 70 years of age is 1000 mg per day; women older than age 50 and men older than age 70 require 1200 mg per day 1.
- Consumption of calcium-rich foods and beverages is the preferred approach to ensuring adequate calcium intake, and supplements should be considered when dietary intake is inadequate 1.
From the FDA Drug Label
Directions - Adults and children 12 years and older chew and swallow 1 to 2 chewable tablets every 2-4 hours as needed. Do not exceed 5 chewable tablets in 24 hours. Do not take more than 5 chewable tablets in a 24-hour period, or use the maximum dosage for more than 2 weeks, except under the advice and supervision of a physician.
The recommended dosing for oyster shell, which is calcium carbonate, is:
- 1 to 2 chewable tablets every 2-4 hours as needed for adults and children 12 years and older
- Do not exceed 5 chewable tablets in 24 hours 2 2
- For children under 12 years, consult a doctor 2
From the Research
Oyster Shell Dosing
- Oyster shell electrolysate (OSE) has been reported to raise serum calcium and increase urinary calcium excretion in vitamin D-deficient states more readily than calcium carbonate 3.
- A study found that 900 mg/day calcium as OSE significantly increased radial bone mineral density in elderly osteoporotic females after 12 and 24 months 3.
- Heated oyster shell-seaweed calcium (AAA Ca) has been shown to be effective in increasing bone mineral density (BMD) in elderly subjects, with a significant increase in lumbar spine BMD compared to placebo 4.
- Nanocalcium from oyster shell has been found to be highly bioavailable and effective in preventing osteoporosis in rats, with zinc-activated nanopowdered oyster shell (Zn-NPOS) showing greater recovery from ovariectomy-induced bone loss compared to powdered oyster shell (POS) 5.
Comparison with Other Calcium Supplements
- A study compared the bioavailability of calcium carbonate powder and calcium citrate tablets in healthy premenopausal women, finding that a single serving of calcium carbonate powder resulted in greater absorption of total and ionized calcium at 4 hours 6.
- Calcium carbonate is considered the most cost-effective form of calcium supplement, but should be taken with a meal to ensure optimal absorption 7.
- Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or protein-pump inhibitors 7.
Dosage and Administration
- The maximum dose of elemental calcium that should be taken at a time is 500 mg 7.
- Oyster shell dosing has been studied at various doses, including 900 mg/day calcium as OSE 3 and 900 mg/day Ca as AAA Ca 4.
- The bioavailability of calcium supplements can vary depending on the form and dosage, with some studies suggesting that once-daily dosing is important for long-term compliance 6.