Using eggshells as a source of calcium

Short summary

Eggshell calcium looks like a good source of calcium. It's generally low in heavy metals, reasonably absorbable, and inexpensive.

If you want to buy powdered eggshells:

If you want to buy a capsule version:

I'm only aware of two eggshell calcium capsule products. Both have more ingredients than I'd prefer, but could be good in a pinch:

If you want to make your own:

Absorbability and effectiveness

Eggshell calcium supplementation is not heavily studied, but the few studies I've been able to find all support its absorbability:

Some people have mentioned digestive irritation with eggshell calcium. I'm wondering if too coarse of a grain size or insufficient stomach acid are the cause. If you have any experience or thoughts on this, please leave a comment.

What's in eggshells?

Logo of the Poultry Science Association

That is one cocky chicken.
...
Heh.

I'm sure the journal of the Poultry Science Association needs no introduction. We all have fond childhood memories of curling up by the fireplace and reading The Control of Bacillary White Diarrhea in Forced Draft Incubators by High Humidity. However, some of us may not have seen their more-recent analysis of the composition of eggshells, concluding that the composition of eggshell calcium appears to vary based on the chicken's diet and environment, but is high in calcium (~39%) and probably reasonably low in heavy metal content.

The analysis also compared Slovakian battery chicken eggshell calcium samples to samples of refined calcium carbonate and oyster shell calcium, along with comparing Dutch eggshell calcium from hens raised in different conditions. Here are their results combined together, with additional values from a 2012 analysis of F.O.F. International's eggshell calcium:

Aluminum
Slovakian eggs <5 μg/g
Dutch "four cereal" eggs 2 μg/g
Dutch "basically pastured" eggs 2 μg/g
Dutch battery eggs 2 μg/g
Japanese eggs 5 μg/g
F.O.F. International organic eggs unknown
Refined calcium carbonate 7 μg/g
Oyster shell calcium 4,400 μg/g
Cadmium
Slovakian eggs <50 ng/g
Dutch "four cereal" eggs 18 ng/g
Dutch "basically pastured" eggs 24 ng/g
Dutch battery eggs 3 ng/g
Japanese eggs <50 ng/g
F.O.F. International organic eggs unknown
Refined calcium carbonate 657 ng/g
Oyster shell calcium 62 ng/g
Lead
Slovakian eggs <0.50 μg/g
Dutch "four cereal" eggs 1.10 μg/g
Dutch "basically pastured" eggs 1.30 μg/g
Dutch battery eggs 0.53 μg/g
Japanese eggs <0.50 μg/g
F.O.F. International organic eggs <0.002 μg/g
Refined calcium carbonate 0.99 μg/g
Oyster shell calcium 0.72 μg/g
Mercury
Slovakian eggs <0.2 μg/g
Dutch "four cereal" eggs <0.2 μg/g
Dutch "basically pastured" eggs <0.2 μg/g
Dutch battery eggs <0.2 μg/g
Japanese eggs <0.2 μg/g
F.O.F. International organic eggs <0.002 μg/g
Refined calcium carbonate <0.2 μg/g
Oyster shell calcium <0.2 μg/g
Flourine
Slovakian eggs 3.75 μg/g
Dutch "four cereal" eggs 6.00 μg/g
Dutch "basically pastured" eggs 5.50 μg/g
Dutch battery eggs 3.00 μg/g
Japanese eggs unknown
F.O.F. International organic eggs unknown
Refined calcium carbonate 25.00 μg/g
Oyster shell calcium 70.00 μg/g
Iron
Slovakian eggs 22.4 μg/g
Dutch "four cereal" eggs 23.0 μg/g
Dutch "basically pastured" eggs 23.0 μg/g
Dutch battery eggs 22.5 μg/g
Japanese eggs 27 μg/g
F.O.F. International organic eggs unknown
Refined calcium carbonate 36.0 μg/g
Oyster shell calcium 420 μg/g

Many of those results surprise me, with battery eggs surprisingly low in heavy metals. It's possible that pastured hens have a more varied diet that increases both increase egg nutrients and eggshell heavy metals.

I conclude from the analysis that it's not worth being too obsessive about the source of the eggshells you use, unless you're able to get an analysis done on them.

Making your own eggshell powder

Here's how I make my own eggshell powder:

Supplies:

Instructions:

Step 1: cleaning the eggshells
  • Option 1: killing pesky microbes without cleaning

    If you're confident of the source and cleanliness of your eggshells, it might be worth preserving the membrane in the eggshells for its potential health benefits. However, I suspect this may make the end product more prone to spoilage.

    • To take this approach, bake the eggshells for 10 or more minutes at 170°F. This should kill most bacteria.
  • Option 2: cleaning and killing pesky microbes at the same time

    If your eggshells are store-bought, they may be treated with chlorine and/or mineral oil, and I think it's worth trying to clean them.

    • To take this approach, rinse the outside of the shells and then put them in a large pot.
    • Boil them for 15-20 minutes. This also separates most of the membrane, which you can remove if you're concerned about long term storage. It's easiest to do this while the water is still boiling by scooping out floating solids and the foamy ring that will form.
      Eggshells in boiling water

      This is not actually a portal to a terrifying alien dimension, it's what the water looks like after a few minutes of boiling.

    • Allow the eggshells to dry completely (you can bake them to speed up the process).
Step 2: smashin' the eggshells
  • This is the fun step. Put the eggs in a bowl and smash 'em while making Incredible Hulk noises. They only need to be broken down to a size that can make it through the coffee grinder, but I give them a few extra smashes to show them who's boss.

    Eggshells being smashed
    Smashed eggshells
Step 3: grindin' the eggshells
  • Put the eggshells in the grinder, and grind them on the finest setting available.

    Eggshells running through the coffee grinder
  • If there's still a lot of visible eggshell shards that snuck past the grinder, it can be worth running everything through the grinder a second time.
Step 4: separating out the fine powder
  • Use a fine-mesh sifter or strainer to separate out the fine powder that you'll be consuming from any larger chunks.

    Eggshell powder being sifted

    I think this is an important step to prevent digestive irritation. Even with my fancy burr grinder and two rounds of grinding, I still had leftover eggshell shards:

    Eggshell powder remains after being sifted
Step 5: storage and consumption
  • Especially if you've removed the membrane, the powder should be very stable and shouldn't require special storage.
  • I'd suggest consuming the powder by dispersing it in whatever you're drinking, it's pretty flavorless.
  • If you need a precise dosage, a sensitive scale will be important. There should be around 400mg of elemental calcium in 1000mg of the eggshell powder.
  • For more casual dosing, a half teaspoon of eggshell powder might contain (very roughly) 500mg of elemental calcium, but depends on how finely the powder has been ground.

Pet eggshell calcium

I'm only aware of three brands of eggshell calcium for pet use:

Conclusion

Eggshells are great, you should pulverize and devour them. But be nice about it.

Eggshell about to be smashed

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