Comparing Calcium Content: Egg Shells vs. Oyster Shells
When evaluating which of these natural sources contains more calcium, a closer look at their mineral composition is necessary. Both egg shells and oyster shells are predominantly composed of calcium carbonate ($CaCO_3$). However, the precise percentage of elemental calcium can differ, as can the presence of other trace minerals that affect absorption and utility.
Oyster Shells: A Potent and Consistent Source
Oyster shells are widely recognized as a high-quality, consistent, and bioavailable source of calcium. Commercially processed oyster shell supplements often contain a very high percentage of calcium carbonate, with some studies citing levels as high as 98%. For example, dried oyster shell has been analyzed to contain between 35.20% and 37.12% elemental calcium. The calcium in oyster shell is typically in a form that is readily and slowly released, allowing for better absorption and utilization, particularly in livestock. This slow-release property is advantageous for certain applications, like improving eggshell quality in laying hens over an extended period. In addition to calcium, processed oyster shell typically contains very few other minerals, making it a pure and reliable supplement.
Egg Shells: The Bioavailable Kitchen Scrap
Egg shells, often a kitchen waste product, are another excellent source of calcium carbonate, composing 90-95% of the dry shell mass. The elemental calcium content in processed eggshell powder typically ranges from 33% to 35%. While the total elemental calcium might be slightly less than in some oyster shell preparations, some research suggests that eggshell powder's calcium may be absorbed more effectively by the body than pure calcium carbonate supplements. This is possibly due to the organic compounds and proteins present within the eggshell matrix. Moreover, the eggshell membrane contains beneficial nutrients such as collagen, glucosamine, and chondroitin, which have potential benefits for joint health. This makes eggshell powder a valuable, low-cost supplement for human and pet diets, provided it is properly sanitized and finely ground.
Comparison Table: Egg Shells vs. Oyster Shells
| Feature | Egg Shells | Oyster Shells |
|---|---|---|
| Elemental Calcium (%) | ~33-35% | ~35-38% |
| Calcium Compound | Calcium Carbonate | Calcium Carbonate |
| Purity/Consistency | Can vary depending on hen's diet. | Typically more consistent and purer. |
| Bioavailability | High, possibly enhanced by organic compounds. | High, particularly known for slow, steady absorption. |
| Additional Nutrients | Contains membrane with collagen, glucosamine, etc.. | Primarily calcium carbonate with minimal trace minerals. |
| Cost | Free (from kitchen waste). | Inexpensive, especially when sourced from seafood industry byproduct. |
| Preparation | Requires sanitizing (boiling/baking) and grinding. | Often sold pre-crushed for convenience. |
Practical Applications
Use for Humans
Both eggshell and oyster shell powder are viable options for human dietary supplements. For a zero-waste, low-cost approach, homemade eggshell powder is effective and well-absorbed, offering a bonus of potential joint support from the membrane. Commercially available oyster shell calcium supplements are convenient and offer a consistent, high dose of calcium carbonate. Always consult a healthcare provider before starting any new supplement regimen to ensure proper dosage and suitability for your health needs.
Use in Gardens
For amending garden soil, both crushed eggshells and oyster shells can be used to add calcium and increase pH in acidic soil. Oyster shells, with their slower breakdown rate, offer a more long-term, sustained release of calcium into the soil. Eggshells, especially when ground finely, break down more quickly, providing a faster, though less prolonged, boost of calcium. Neither should be considered a complete fertilizer, as they lack other essential nutrients like nitrogen, phosphorus, and potassium.
Use for Pets
Many pet owners use eggshell powder as a calcium supplement for dogs and other pets, especially those on a raw or homemade diet. It is crucial to ensure eggshells are from a safe, reputable source and properly sanitized before grinding into a fine powder to prevent injury or bacterial contamination. Oyster shell is also widely used as a supplement for laying hens to improve eggshell quality. For pets, proper balancing of minerals like calcium and phosphorus is vital, so always consult a vet to ensure nutritional needs are met.
Conclusion
In the debate over what has more calcium, egg shells or oyster shells, oyster shells often edge out egg shells slightly in terms of pure elemental calcium percentage, especially in commercially prepared supplements. However, the difference is marginal, and other factors are equally important. Eggshells offer the benefit of a sustainable, cost-free source, along with beneficial compounds in the shell membrane for joint health. Oyster shells provide a highly consistent, bioavailable, and often slow-releasing form of calcium carbonate. The "better" choice ultimately depends on the specific application. For convenient, high-purity supplementation, oyster shell is a reliable choice. For a cost-effective, zero-waste, and readily available option that offers a blend of benefits, eggshell powder is an excellent alternative.
Sources for Calcium Supplementation
For those seeking reliable information on calcium supplementation from eggshells, an authoritative resource can be found on Healthline's article on the benefits and risks of eating eggshells. This detailed guide provides background on calcium content, bioavailability, and preparation methods for safe human consumption.
Key takeaways
- Higher Calcium: Oyster shells generally have a slightly higher percentage of elemental calcium than egg shells.
- Superior Absorption: Eggshell calcium is highly bioavailable, potentially even more so than standard calcium carbonate supplements.
- Cost and Availability: Eggshells are a free and sustainable byproduct, while oyster shells are an inexpensive commercial alternative from seafood waste.
- Slow Release: Oyster shells are prized for their slow calcium release, which is particularly beneficial for livestock like chickens.
- Additional Nutrients: Eggshells contain a membrane with collagen and other compounds that may support joint health.
- Safe Preparation: Both must be sanitized properly before consumption or application to avoid bacteria.
How to Prepare Egg Shells and Oyster Shells
Preparing Egg Shell Powder
- Sanitize: Boil clean eggshells in water for 10–15 minutes to sterilize them.
- Dry: Spread the shells on a baking sheet and bake at 200°F for 10-20 minutes until completely dry.
- Grind: Use a coffee grinder or blender to process the shells into a very fine powder.
- Store: Keep the powder in an airtight container in a cool, dry place.
Preparing Oyster Shells
- Source: Purchase pre-ground oyster shell from a feed or garden supply store for convenience.
- DIY Method: If sourcing raw shells, boil them thoroughly to sanitize and dry in the oven.
- Crush: Use a heavy tool or industrial grinder to crush the shells into the desired particle size.
- Use: Mix crushed oyster shells into soil or animal feed as needed.
