Animal Information

What are the Calcium, Vitamin, and Mineral Needs of Tortoises

Many people are unclear as to the difference between vitamins and minerals, and especially about how the two interact. Many minerals, calcium, for example, depend upon the presence of certain vitamins such as vitamin-D before they can be absorbed.

Vitamins are organic substances which help regulate bodily functions. Acting as co-enzymes, vitamins aid the action of enzymes during the metabolism of dietary nutrients.

There are about a dozen major vitamins, a deficiency of any one of which will result in a serious deficiency disease.

Vitamins are only required in relatively small quantities but have a major effect upon the body’s reproductive, digestive, nervous and muscular systems. Vitamins also affect tissue growth and anti-body production.


Important to the condition of the skin and mucous membranes, eye (especially retinal) condition, biochemical and reproductive functions.

Plants contain carotene which is converted to true vitamin-A in the body. A deficiency is called hypovitaminosis.


The B-complex vitamins are water-soluble and excesses are excreted in the urine. Click to read Why Soaking Tortoises Is Important for more information on urine and urates.

Vitamin B1, thiamine, is a regulator in the carbohydrate metabolism; Vitamin B2, riboflavin, is a co-enzyme in energy release and interacts with vitamin B6 and vitamin B12.

Vitamin B3, niacin, is also crucial to energy metabolism and is often obtained by converting the amino-acid tryptophan. This process also requires the presence of thiamine, riboflavin, and pyridoxine.

Vitamin B6, pyridoxine, is involved in energy conversion from glycogen and in the synthesis of haemoglobin and antibodies.

Vitamin B12 interacts with folic acid to govern the production of red blood cells. A deficiency causes pernicious anemia and neurological symptoms.

This vitamin is only produced within the gastrointestinal tract when various micro-organisms act upon trace level cobalt.

Deficiencies can occur following malabsorption syndrome or as a consequence of severe parasite infestations.

The B-complex is just that. A matrix of interacting and inter-dependant compounds.


Sometimes called ‘the sunshine vitamin’, vitamin-D is a fat-soluble vitamin which is essential to the absorption and utilization of calcium and phosphorous, as such, it plays a major role in bone formation.

It can be obtained either naturally, by the action of ultra-violet light on sterols in the skin, or orally by supplementation.

Virtually all specialist calcium/mineral supplements intended for reptile use contain vitamin D in sufficient quantity.


Vitamin-C has many functions, but as it is present in almost all fruits and green vegetables, deficiencies are extremely unlikely in tortoises.

Vitamin-E is an antioxidant that works in conjunction with vitamins A and C.

A fat-soluble coagulation vitamin. Vitamin-K isvsynthesized in the gut by bacterial action and is also found in plant foods.

It is especially abundant in green, leafy plants.

Minerals are quite different from vitamins and are both chemical regulators and construction materials. Calcium forms a major part of a tortoise’s body, more than any other mineral.

Calcium deficiency is also extremely common as a growing tortoise requires substantial quantities of this mineral in order to build its skeleton. Click to read about Growth And Prymiding In Tortoises.

 The building of healthy bone tissue is the result of many vitamins and minerals acting in cooperation with each other.

 It is essential to note that calcium is poorly absorbed by the body whereas phosphorus is readily absorbed – if a diet is heavy in phosphorus in relation to calcium, the excess phosphorus will prevent the uptake of calcium to the bone.

It is very easy to feed a diet too concentrated in phosphorus because it is available in nearly every foodstuff whereas calcium is relatively rare. We must knowingly choose calcium-bearing foods when designing diets for captive animals.


Calcium and phosphorus together account for three-fourths of the mineral elements in the body, and five other elements account for most of the rest. It is important to note that their actions are interrelated; no one mineral can function without affecting the others.

The major function of calcium is to act in cooperation with phosphorus to build and maintain bones. Calcium is essential for healthy blood and also helps to regulate heartbeat.

In addition, calcium assists in the process of blood clotting and helps prevent the accumulation of too much acid or too much alkali in the blood. It also plays a part in muscle growth, muscle contraction and nerve transmission.

Calcium aids in the body’s utilization of iron helps activate several enzymes (catalysts important in metabolism) and helps regulate the passage of nutrients in and out of cell walls.

Calcium absorption is very inefficient. Two factors affect absorption directly; the availability of calcium in the diet and the current body need. Unabsorbed calcium is excreted.

Certain substances interfere with the absorption of calcium.

When excessive amounts of fat combine with calcium, an insoluble compound is formed which cannot be absorbed. Other substances that can disrupt this process include oxalates and phytic acid.


Phosphorus is the second most abundant mineral in the body. It functions along with calcium. A balance of calcium and phosphorus is needed for these minerals to be effectively used by the body.

Phosphorus plays an important part in almost every chemical reaction within the body. It is important in the utilization of carbohydrates, fats and protein for growth, maintenance, and repair of cells and for the production of energy.

It aids in the transference of heredity traits from parents to offspring. It is also necessary for proper skeletal growth, kidney function and transference of nerve impulses.

If phosphorus content is high, additional calcium must be taken to maintain proper balance. Phosphorus is available in a wide variety of foods and further supplementation is not necessary.

Miscellaneous Elements

Calcium, chlorine, phosphorus, potassium, magnesium, sodium, and sulfur are present in relatively high amounts in the body tissues.

Other minerals are present in the most minute quantities but are essential for proper body functioning. Iron, copper, and fluorine are present in sufficient quantities from deep green leafy plants.

Iodine is needed to maintain a positive calcium balance, so a multi-mineral mixture containing iodine should be provided in addition to supplementation of raw calcium.

In nature, tortoises obtain their calcium requirement in several ways.

The bulk of their requirement is typically supplied by consuming calcium-rich vegetation.

This vegetation is itself typically growing on calcium-rich soils, a situation that leads to plants that are themselves rich in this mineral.

Tortoises also obtain some additional calcium by incidental consumption of sand/soil particles when feeding, and by deliberately seeking out calcium-rich items in their environment, such as snail shells or sun-bleached bones.

Surprisingly, even desert environments often have extremely large snail populations.

It is not unusual to find literally hundreds of estivating snails per square meter and thousands of particles of broken snail shell in the same area.

Tortoises have been observed to seek these out, and to consume them enthusiastically. They provide a concentrated, readily absorbed source of this vital mineral.

In most captive situations, the gross calcium content of the diet rarely, if ever, approaches that of wild diets.

Click to purchasePlantago 

The calcium-to-phosphorus ratio of captive diets is also typically far lower overall than is seen in the wild. Some typical examples include Plantago sp., with Ca:P ratios of above 20:1 and Opuntia sp., where Ca:P ratios can be as high as 78:1.

The typical diets adopted by many keepers, based upon commercial salads and fruit, often contain little calcium and an excess of phosphorus.

One problem in relying exclusively upon dietary selection is that many plants that on the surface appear to offer good, or positive calcium-to-phosphorus ratios, also contain chemicals that inhibit calcium take-up.

Mustard greens, turnip greens, kale, cabbage, bok choy, spinach, chard and collard greens all fall into this category. One of the best known examples of such an ‘anti-nutrient factor’ is oxalic acid. Another is phytic acid, found in high concentrations in peas, beans and related legumes.

 It is therefore necessary to screen diets not only for gross calcium content, and calcium-to-phosphorus ratio, but also to screen them to exclude reliance upon plants that contain high levels of these ‘anti-nutrients’. In practice, this is fairly difficult to achieve on an all-year-round basis.

Calcium supplements

Calcium may be delivered in various forms, some of which are more readily absorbed and efficient than others.

Calcium supplements based on the bone meal are inadvisable due to their inherently high phosphorus content (24% calcium and 12% phosphorus).

As most tortoise diets are already rich in phosphorus, supplementing with additional phosphorus is neither necessary nor recommended.

According to a recent review of calcium preparations, there are at least a dozen common calcium preparations and hundreds of different formulations available.

Calcium carbonate is the most common preparation; some others include tricalcium phosphate, dicalcium phosphate, bone meal, calcium citrate-malate, oyster shell, calcium lactate, and calcium gluconate.

These calcium preparations differ in a variety of ways. Calcium carbonate has the highest concentration of calcium by weight (40%), whereas calcium citrate has 21% calcium and calcium phosphate has 8% calcium by weight.

Although calcium carbonate has the highest concentration of calcium by weight, this form of calcium is relatively insoluble, especially at a neutral pH. In contrast, calcium citrate, although containing about half as much calcium by weight, is a more soluble form of calcium.

Certain preparations of calcium (e.g., bone meal, dolomite) may contain contaminants such as lead, aluminum, arsenic, mercury, and cadmium. Significant amounts were identified in calcium carbonate supplements labeled oyster shell, for example.

Chronic intake of these supplements may pose an unnecessary risk. Most commercial calcium preparations are tested for heavy metal contamination.

In theory, excessively high intakes of calcium may interfere with the absorption of other nutrients such as iron and zinc, however, in chelonia we are not aware that such effects have been demonstrated.

Other potential adverse effects of chronic intakes of high doses of calcium include Hypervitaminosis-D. Recent human studies indicate that increased intake of calcium does not increase the risk of kidney stones.

However, restricting dietary calcium may increase urinary excretion of oxalate which in turn increases the risk of kidney stones in addition to causing bone developmental problems.

As a general rule, calcium carbonate is the preferred source for use as a routine supplement. It is both safe and effective. Limestone powder is available at very low cost in bulk from agricultural feed merchants, and approaches calcium carbonate in efficiency.

For emergency use, where commercial supplements or limestone powders are not available, human calcium tablets may be ground to a fine powder and applied to the food liberally (note that while some human calcium tablets may also contain vitamin D, this is usually in the form of D2 rather than D3 as required by reptiles).

Calcium With Vitamin D3

While it is true that these do contain useful amounts of calcium (up to 39% available Ca), and have been shown in human studies to help prevent osteoporosis in mammals, it should be noted that for chelonian use, there are a number of potential drawbacks.

Calcium Without Vitamin D3

These include the fact that studies show that such eggshell material also contains hormone traces (with unpredictable effects upon tortoises) and that any remaining egg membrane material can also contain antibiotic traces as well as representing a potential reservoir for contamination by salmonella organisms.

Turtle Blocks

One form of calcium supplement often sold in pet stores is known as “turtle blocks”. These are mostly made of Plaster of Paris (calcium sulfate hemi-hydrate) combined with calcium carbonate, often in a 50-50 combination. Plaster of Paris itself contains almost no useable calcium and is merely used to adhere the block into shape.

Weight-for-weight, therefore, “turtle blocks” contain 50% or less calcium carbonate, of which, in turn, only 40% may be bioavailable. There are also concerns over heavy metal contamination in gypsum, from which Plaster of Paris is derived. This is not a form of calcium supplementation that we therefore recommend.

On balance, the safest and most effective calcium supplements for routine use with captive tortoises would appear to be a calcium carbonate based, phosphorus-free ground calcium powder. preferably of commercial quality, either with or without added vitamin D3.


Vitamin D3 plays a pivotal role in bone formation, allowing the body to absorb calcium, and for maintaining the proper balance of calcium and phosphorus. A tortoise could eat calcium all day long, but if it was not getting an adequate amount of vitamin D3, it would not be able to absorb it properly.

In nature, herbivorous tortoises acquire all of their vitamin D3 requirements as a result of a chemical reaction in the skin, following exposure to the UV-B spectrum of sunlight. A compound is formed that is known as 7dehydroxycholesterol (this is sometimes also shortened to 7DCH or provitamin D).

This is converted, by means of temperature, to vitamin D proper. It is vital that both sufficient UV-B plus adequate basking temperatures are available if this process is to function properly. This is one reason why the new UV-B heat lamps (self-ballasted Mercury Vapour lamps) are so good.

They provide both UV-B and the heat necessary to convert the 7DCH to a form that can ultimately be utilized by the calcium metabolism. A UV-B fluorescent tube alone will not do this. If such a tube is used, a separate source of basking heat is mandatory. Without an adequate source of heat, the conversion will not take place efficiently.

The degree to which you may need to use a supplement containing vitamin D3 will vary according to several factors, principal among these being how far north you are situated, and the number of hours exposure to natural sunlight your animals receive or the type and intensity of UV-B supplemental lighting employed.

As a general rule, if you live in an area where tortoises and turtles occur naturally and your animals are able to spend at least three or four hours outdoors in unfiltered sunlight daily, you probably do not need to rely upon oral D3 supplements.

Phosphorous Free Calcium Supplement

A calcium supplement alone should suffice. If you live in a northern, cloudy area where tortoises and turtles do not occur naturally, or your animals’ outdoor time is restricted, it is recommended that you do use a supplement on a regular basis.

We would suggest three times per week as an absolute minimum. If you provide high output UV-B lamps and have adequate basking facilities, you may be able to rely upon these to promote adequate D3 synthesis but personally, I would prefer to hedge my bets by supplementing with calcium and D3 supplement orally at least twice a week.

Calcium and Vitamin D3 are certainly not the only components required to facilitate healthy bone development in tortoises and turtles:

• Magnesium is essential for proper calcium absorption and is an important mineral in the bone matrix. It has specific effects on the parathyroid hormone, which helps regulate proper calcium metabolism.

• Phosphorus is the second most prevalent mineral in bones and makes up more than half the mass of bone mineral. Thus, the diet needs to have sufficient phosphorus in order to build healthy bones. For most tortoises and turtles, this is not a problem, as most vegetation is rich in this element.

When phosphorus levels in the blood are too high, however, the body takes calcium out of the bones to bind with the phosphorus to facilitate its removal from the bloodstream. Bones can become brittle or deformed as a result.

Many other micro trace elements are also important, including Manganese, Zinc, Boron and Strontium. These may not be provided by a regular calcium or calcium with D3 supplement alone.

An appropriate and varied diet will certainly provide most of them, but a wide-range mineral supplement can also be used to ensure that they are present on a regular basis. We would recommend such a supplement be used no more than once weekly.


Cuttlebone is made of aragonite, that is, crystallized calcium carbonate. This mineral has a beautiful lattice shape, which explains its buoyancy and absorbent power.

Apart from this huge amount of calcium carbonate, cuttlefish shell includes different essential trace elementsvwith varying composition percentages in its composition.

Among the nutrients of cuttlebone, you can also find calcium phosphate.

It also contains calcium phosphate, sodium, magnesium, phosphorus, and other mineral salts.


We are not sponsored by Repcal. But would love to be!

An exotic pet owner should provide cuttlebone, vitamin supplement, natural diet, and commercial foods. All of these are our weapons against Metabolic Bone Disease. This is an umbrella term referring to abnormalities of bones caused by a broad spectrum of disorders.

Rep-Cal is formulated to ensure proper growth and health by providing complete and balanced nutrition. It is a veterinarian recommended food containing natural plant and fruit ingredients tortoises love and provides the 100% complete daily nutrition they need.

Rep-Cal Tortoise Food has been tested successfully by reptile veterinarians. It is fortified with optimal levels of vitamins and minerals like calcium and Vitamin D3 so no other food or supplements are required.


Yup, bone! The eating of bones, called osteophagy, is well known in turtles. The behavior has been recorded in several species kept in captivity.

Osteophagy has been regarded as a beneficial behavior to combat mineral deficiencies in animals.

Osteophagia practices have also been observed to be detrimental to the dental works of herbivores.

It has been observed that the pattern of wear on the cheek teeth of herbivores is congruous to the manner in which herbivores hold and chew bones.

An interesting observational study of tortoises near St. George, Utah, found that the tortoises exclusively consume the Mojave Desert’s white stones composed of calcite (mostly calcium carbonate).

As opposed to the brown, grey, or other colored stones. The ingestion of these white stones is attributed to the deliberate intake of additional calcium.

Furthermore, it is thought that these additional sources of food are sources of not only calcium, but also other nutrients including phosphorus, sodium, iron, copper, and selenium.

In addition to desert plants, desert tortoises also consume vulture feces (which contain bones), soil (layers contain calcium), mammal hairs, feathers, arthropods, stones, bones of conspecifics, as well as snake and lizard skin castings,

Let us know your ideas and comments below!

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