Calcium & Reptiles | What Do We Really Know?

Authored by John F. Taylor of Reptile Apartment

Calcium and Reptiles | What we think

Calcium for reptiles

Calcium Supplement

Calcium specifically but overall vitamin and mineral supplementation is something that is and has been ‘guessed’ at for as long as we have been keeping reptiles. Type in the search string calcium supplementation reptiles and out of the top ten search results you get only two dealing with dosage and related subjects. The rest is online stores or websites selling reptile calcium. We all know, or should know, there are hundreds of sources of calcium available to the reptile caregiver.
Let’s take this one step further, with a refined search veterinarian articles on calcium supplementation dosage in reptiles. We get some narrower results, but almost too narrow now. Scholarly articles refer us to calcium content of the diet offered to leopard tortoises, urinary diseases in reptiles, and dystocia in oviparous lizards. Still not too helpful is it? We then scroll down to a myriad of articles regarding MBD or metabolic bone disease.

Why Calcium?

Calcium provides reptiles (indeed, all vertebrates) with  an important mineral they need for proper bone growth, nerve function, hormone synthesis, and the extra calcium female reptiles must have to produce viable eggs. It is understood snakes need calcium too, in my experience they do not need to have their foods dusted with a calcium supplement. When a snake ingests a prey item all the nutrients are absorbed from the prey, and most captive snakes are fed prey items with an endoskeleton. This endoskeleton provides the necessary calcium for proper bone growth and the laying of eggs in female snakes. This being the case, there is no reason I, nor my colleagues have seen for providing extra calcium supplementation to snakes. With that said some breeders do dust during breeding season to increase chances of viable eggs.

Lizards in captivity are a whole different story; especially insectivorous and herbivorous lizards. Because we cannot replicate the exact diet of our captive lizards we have to “supplement” it with other vitamins and minerals, calcium in particular is the one most often lacking and sending numerous reptiles to the veterinarian.

Believe it or not, lizards don’t get their prey items dusted in the wild at the local calcium store. Shocking I know, but trust me on this one, they do not go to the local calcium supplier and get “dusted.”

Wild Diets

We as keepers (this will irritate some folks but it is a sad fact I see every day) are lazy. Let me explain.

I can, as my dad would say,

“Bet dollars to doughnuts”

Many readers have not gone out of their way to research their pet reptiles’ wild diet. This has led to  one of the greatest disservices we could do to our captive reptiles. Wild diets of many captive reptiles have been documented and are available if you know where and how to find them.

The Uromastyx species of lizard are gaining in popularity. I published a book on them a number of years ago. Uromastyx Complete Herp Care (affiliate link) In the book’s original form, I covered the wild diet more in-depth than what was published. I went so far as to make contacts with researchers in the field documenting what was being eaten. To my amazement, Uromastyx were not going to the local grocer and picking up the organic spring mix we feed them in a captive environment. They were eating grasses, seeds, flowers, and leaves. It’s documented at least one species, U. microlepis, had regularly ingested soil (calcium supplementation)? This behavior is known scientifically as geophagy.

We should replicate our reptiles diet closer to what they eat in the wild whenever possible; we being creatures of comfort and ease, have discovered what is necessary to keep our animals alive with the minimum amount of expense of labor and cost.

  • Do you understand your pets’ “wild diet”?
  • have you read an actual scientific paper written about the reptile’s diet in the wild?
  • Do reptiles “know” how much calcium their bodies require?
  • Why would they participate in geophagy? There’s your $10 word for the day kids. It means literally ‘earth eating, and refers to how lizards would get a significant amount of vitamins and minerals.

This of course goes without recognizing most herbivorous reptiles would probably get their dietary intake of minerals and vitamins directly from the plants they were eating in the wild. Nutrients are absorbed by the plants naturally from the soils where they grow. When a lizard then eats the plants they obtain the nutrients the plants had absorbed.


Calcium Dosage should be a straightforward process we would think. Calcium is calcium what’s to know.

Directly from two different manufacturers of calcium supplementation products:

“Place two spoonfuls into a bag with insects and shake well until coated. For mice, dip only the hindquarters in the supplement. May also be sprinkled over fruits and vegetables. For daily use.”

“Sprinkle the amount needed to evenly coat insects or pinkie mice.”

Why are the above statements alarming, you may ask?

The following is a direct quote from our report Solving the Calcium Conundrum with Dr. Robert Sprackland

“OK, now we know a lot about vitamin D3 production and activation in humans, some other mammals and a few birds. Everything that has been extrapolated about reptiles and vitamin D3 has come from the human mammal model…”

We as humans really don’t understand  calcium processing in reptiles. I am aware of no studies of the calcium in the blood of healthy reptiles giving us a benchmark of sorts for any  particular species. In Manual of Exotic Pet Practice the authors mention specifically that ionized calcium (which is what we find in tested the blood calcium levels when testing for MBD) is often not part of a regular “blood workup.” They also mention there are other factors which can affect the calcium readings, such as age, sex, and reproductive status of the animal  in question.

Calcium Overdose

Hypercalcemia is a serious condition where there is too much calcium in the bloodstream, and it may  cause serious health issues in reptiles. One major effects of calcium overdosing is renal failure, a fatal condition. When I tell  people who ask about calcium dosage, the next question to usually follow is:

“Well, how much is too much?”

A valid question, to which there is sadly and honestly. No viable answer.

So what is a reptile owner to do?

We will get to that soon I promise, there are a few more subjects regarding calcium we need to cover. As if there weren’t enough issues with just dosage; we then have to contend with ‘types’ of calcium supplementation.

Types of Calcium

We scan the shelves of the local pet store and see all types and variations of calcium supplementation. There’s liquid calcium, powdered calcium, and  calcium fortified with vitamins, and often with  vitamin D3. So which one is right for your reptile and how do we know? To answer that, we have to get a better idea of why and how calcium operates in our reptiles’ bodies, which we as humans understand poorly at best.

  • Liquid calcium is probably absorbed better than would be powdered forms. With that said we again have no idea how much is too much.  
  • Calcium powder, available  as calcium carbonate, provides reptiles with the boost of calcium they need for proper bone growth and the extra calcium for female reptiles which may be gravid to produce viable eggs. 
  • Fortified calcium is calcium having other trace elements added, or maybe it  just has vitamin D3. Vitamin D3 is a byproduct of your reptiles’ ability to absorb and process calcium naturally. 

For an excellent treatment on reptile supplementation I recommend Olimpia Martinotti and her piece on MuchAdoAboutChameleons | Are All In One Supplements Really Better?

Calcium Absorption

Calcium can be processed without vitamin D3 in a process called fusion absorption. Fusion absorption doesn’t allow for most of the calcium to be absorbed, so much of the calcium is therefore excreted. Vitamin D3 assists in the absorption of calcium  by making  it more usable or soluble. This makes it easier for the calcium to be absorbed across cell membranes.

This brings us to yet another conundrum when dealing with calcium and our scaly friends. A number of reputable herpetoculturists and scientists have reported ultraviolet light (UV) is unnecessary if we use calcium fortified with D3. This particular claim I have heard of concerning monitor lizards,  and a well-known Uromastyx breeder has personally reported to me that he has done some trials and measured the effects of exposure to UV with and without D3 supplementation. In his findings, he stated he saw no discernible difference in the lizards which were given only D3 supplementation and no UV exposure versus those exposed to UV and given only calcium supplementation.

In humans, exposure to UV is what converts the precursor for vitamin D3 into the active and essential vitamin D3. If the vitamin is provided from the diet, the need for UV is considerably reduced. What does this tell us? It tells us it is indeed possible for some lizards to process calcium by simply fortifying the calcium with vitamin D3. This may not be the case for all lizards and should not be attempted with any captive lizard unless you fully understand the risks of what’s involved.

Calcium Dosage

I would absolutely love to tell you it’s as simple as reading the directions on the bottle of calcium. I would also love to recommend one calcium product over another. Especially if there was an affiliate link to go with it. Alas, there is not one product I can personally recommend and I won’t say what I use because  it  probably makes no difference what calcium supplementation you use.

Can you overdose with calcium? Yes, you can.

With the products currently available it is highly unlikely you would be able to do so if you followed the very limited directions given on the packaging. In my experience you’re more likely to under dose the calcium than overdose it with the current products on the market.

Calcium Blockages

I want to end this review with some comments about something that drives me up the wall: Calcium-blocking vegetables. For the love of everything sacred, yes, some vegetables can and do block calcium, making it extremely difficult or impossible for the mineral to be absorbed from the gut. However, as with all things if these are NOT the staple diet of the reptile then there is no reason these “calcium blocking” vegetables cannot be offered.

It’s a really simple concept; if I stick you in a room without sunlight and feed you spinach every day from birth, you are obviously going to have numerous issues as far as your health is concerned, right?

So there you have it. There are varying pros and cons to varying brands or forms  of calcium, but as far as one being better than another it really depends on what you’re hoping to achieve. Are you simply looking to provide dietary calcium or are you looking for a calcium to provide a gravid female with the needed calcium to produce eggs? Maybe in the next piece we will do a summary of all the vitamins A to Zinc and examine what is necessary and why. We invite you to tell us of your personal experiences regarding calcium supplementation. For a more in-depth treatise on calcium, reptiles, and their needs please see Calcium Series authored by Christina Miller