Using eggshells as a source of calcium

Updated: September 18, 2016

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:

F.O.F. International looked like a great source for straight eggshell calcium powder, but they appear to have disappeared from the internet. If anyone manages to track them down or find a similar alternative, please leave a comment.
There are a few eggshell calcium products available that are meant for pets.

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:

Swanson has Swanson Ultra 100% Natural Eggshell Calcium with Vitamin D3 available directly from the company, or on Amazon. In the UK, HealthMonthly is an affordable source. The ingredients are eggshell calcium, gelatin, magnesium stearate, microcrystalline cellulose (plant fiber), vitamin D-3 beadlets (dl-alpha tocopherol, modified food starch, medium-chain triglycerides, sodium ascorbate, sucrose, silica).
Membrell / Redd Remedies has BONEhealth Original available directly from the company, or on Amazon. The ingredients are eggshell calcium, cholecalciferol (vitamin D3), magnesium citrate, vegetarian capsule (vegetable fiber and water). They appear to be in the middle of reformulating, so older bottles may have magnesium oxide, silicon dioxide, and magnesium stearate.

If you want to make your own:

See my description below.

Remaining contents:

Absorbability and effectiveness
What's in eggshells?
Making your own eggshell powder
Pet eggshell calcium sources
Conclusion

Absorbability and effectiveness

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

Humans
- A placebo-controlled study found increased bone mineral density of the hip when taking eggshell calcium.
- A small pilot study (with no placebo control) found that eggshell calcium powder (when combined with supplemental vitamin D3 and magnesium) improved bone mass in people with osteoporosis or osteopenia, along with a reduction in pain. This suggests that it is well-absorbed and effective for those conditions, at least.
Rats
- A study using an osteoporotic rat model showed eggshell calcium increasing bone mineral density, suggesting it is well-absorbed.
- A study of weanling rats compared eggshell calcium to straight calcium carbonate, showing similar (though strangely varied) absorption results.
Piglets
- Studies using piglets showed better digestibility with eggshell calcium than with purified calcium carbonate.

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?

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:

Eggshells
Your favorite tool for smashing eggshells (a potato masher is pretty fun).
Coffee grinder.
- Burr-grinding: My barista sister in law suggested a Capresso 560 (Amazon, Walmart) for me, and it seems to work well. Two downsides: it's expensive and larger grains can pass through the grinder, requiring multiple grinds to finish.
- Blade-grinding: Dashing rogue Amazoniac suggested the Hamilton Beach 80374 (Amazon, Walmart) as working well, allowing you to grind the powder indefinitely to get the desired powderiness. I insist that's a word.
  
  He mentioned that it allows for a very low sweep of the blade, preventing a problem I ran into with a cheap blade grinder where there'd be a hard-packed layer of incompletely-ground eggshell. You may have to tilt/shake these blade models for more-complete grinding.
Fine-mesh sifter or strainer.

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. 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.
Step 3: grindin' the eggshells	Put the eggshells in the grinder, and grind them on the finest setting available. 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. 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:
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:

Eggshellent Calcium is a straight eggshell calcium powder, but is meant for pets. For those outside the US, Jesse of pet-grub.com will ship anywhere for reasonable prices if you place a large order.
Twin Beaks Aviary's Hatched is an eggshell calcium supplement meant for for birds.
irRAWsistible Eggshell Calcium is available in some Canadian stores.

Conclusion

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