Humans, pets, and domestic animals should always get the proper diet for their species, age and health. However, we don’t always know what the proper diet is, and when we do, we cannot always offer it. For that reason, many people take or offer their animals supplements to help ensure that they get what they need. With tortoises, the key supplements are vitamin D, calcium, iron, and fiber since these are the elements that are hardest to offer with most grocery store foods.

For guidelines on proper doses, see the Nutritional Dosages page.


Vitamins are organic nutrients that are used in small quantities to allow a variety of metabolic functions to work. Think of them as small keys that unlock other processes in the body.

Fat Soluble Vitamins

Fat soluble vitamins do not dissolve in water, and are not flushed out of the system easily. Instead, they are stored in the fatty tissues and organs. This means they can be overdosed more easily than the water-soluble vitamins.

  • Vitamin A is an important vitamin. It is found in dark greens, yellow veggies, organ meats, and eggs. The dosage for reptiles is about 100-200IU’s per kilogram of body weight per day.Too little of it will cause eye and vision problems in chelonians and too much can cause other problems.  IMPORTANT! For various reasons, people, even vets, will quickly blame vitamin A for any eye problems then offer more A to compensate, which actually may cause an overdose! Avoid offering extra A unless the vet does a blood test to ensure that this is really the problem.
  • Vitamin D is the so-called “sunshine vitamin”. It is critical to tortoises (and most reptiles) since it “unlocks” the cells to accept calcium. It is found in unfiltered sunlight, mid-range levels of ultraviolet light (“UVB”), organ meats, oily fish, fungi grown in natural light, and not much else. Reptiles should get 10-20IU’s per kilogram of body weight a day. There are two main forms of D: the weaker D2 in mushrooms, and the preferred D3 from most other sources.
  • Vitamin E is an anti-oxidant, builds the immune system, and is used by the skin. It is found in fruits, vegetables, vegetable oils, and eggs. The dosage should be about 1-2IU’s per kilogram of body weight per day.
  • Vitamin K is one of the essential elements to building healthy bones. It also prevents blood clots and is used in the digestion system. Deficiencies or overdoses are uncommon but can be a problem with a poor diet. It is found in most dark, leafy greens, especially dandelions, kale, spinach, and collard greens.

Water Soluble Vitamins

These vitamins dissolve in water and excess amounts are usually flushed from the body. Most of them take care of themselves in a proper diet.

  • Vitamin B Complex are a series of related water-soluble vitamins that help connective tissues, skin, nerves, blood, etc. They are found in items like eggs, organ meats, legumes, tomatoes, and veggies.
  • Vitamin B13 (orotic acid) is mentioned in a lot of old reptile care books. It is no longer
    considered a vitamin, but is still a nutrient used in the calcium cycle. It is available in many foods, especially root vegetables like carrots and onions. This is one reason shredded carrots are so commonly mentioned in diet lists for tortoises that would not eat carrots or other root vegetables in the wild. Not usually a problem in a varied diet.
  • Vitamin C is the water-soluble vitamin found in citrus that builds connective tissue and fights scurvy in humans. Animals can usually produce their own vitamin C, so it is not a major concern.


“Minerals” in this sense are ions other than carbon, oxygen, nitrogen, and hydrogen that living organisms use for various metabolic processes. They are a lot like vitamins in what they do, but these are based more on a single chemical element. The category is divided into “macro-minerals” that you need significant amounts of, and “micro-minerals” you only need small amounts of.

  • Calcium is the main mineral we focus on in chelonians. Calcium is the basic building block of the skeleton, and is also used by the muscles. It is found in the bones of prey animals, dark greens, fish. Calcium is hard for the body to absorb by itself so vitamin D3 is used to help “unlock” the cells: no “D3”, no calcium. See the section on “Calcium Metabolism” below for more on this. Reptiles should have 1.3-8mg of calcium per calorie of food being offered per day.
  • Phosphorous can be found in most foods and is especially abundant in “grocery store” produce and meats. It is used with calcium to help build tough bones and teeth, but too much will make them soft. See the section on “Calcium Metabolism” below for more. Phosphorous dosage depends on calcium dosage: they should be roughly the same or about twice as much calcium.
  • Magnesium is also used by bones as well as the heart and nerves. It is found in many foods.
  • Potassium is part of the body’s electrical system and is found most abundantly in tomatoes and bananas.
  • Iron is a micro-mineral that is necessary for many functions, including building strong bones. I mention it separately as it demonstrates an interesting phenomena: calcium blocks iron intake. It turns out that almost every nutrient affects other nutrient,  blocking them, or enabling them. This complex relationship is one reason it is so hard to build a “perfect” diet for any animal.
  • Sulfur, Chloride, and Sodium are the last of the “macro-minerals”. These three tend to take care of themselves and are used by important body parts like the nervous system, digestive fluids, etc. They
    are most easily found in a few “un-tortoise-like” foods, but are sufficiently present in most other things that we don’t need to worry about them. A pinch of salt every so often, however, helps insure that the tortoise gets enough sodium, chloride and iodine.
  • Micro-minerals are used by the body in small amounts, and are generally provided by a solid diet. They include chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, nickel, selenium, silicone, vanadium, and zinc.


Probiotics is the term for micro-organisms, like intestinal flora, that help the digestive system and improve overall health. Yeasts, active culture yogurt, and fecal material are rich sources for probiotics, and they are even found in the air. Intestinal flora can be damaged by drugs (like antibiotics), food poisoning, and other stressors (such as shipping or poor care), usually resulting in diarrhea. The intestinal flora builds back up after a short time, but can be sped up by eating a probiotic rich food or supplement, one reason tortoises eat feces.

Calcium Metabolism and Bone Development

Calcium is critical to bone development, and is also important for nerves and other structures. There are two problems with calcium, however: it is not easily absorbed into the cells, and by itself it makes bones too
brittle. In order for calcium to get into cells, they need to be “unlocked” with vitamin D. No vitamin D, no calcium in the cells, it is just that simple.

In order to make bones less brittle, we mix in some phosphorous for toughness, in a ratio of about three to four parts calcium to one part phosphorous. This is called the Calcium:Phosphorous Ratio, abbreviated Ca:P. A good Ca:P would be 2:1, a poor one would be 0.5:1. Too much phosphorus in relation to calcium and the bones get soft. Tortoises are prone to many calcium- and shell-related problems. As a group, these problems are called Metabolic Bone Disorder or MBD. See the “Metabolic Bone Disease” article for more on this.

Besides calcium, phosphorous, and vitamin D, strong bones need other things as well: vitamin K, iron, magnesium, and water. The animal also needs proper exercise and rest, warmth,and manageable amounts of stress.

For an interesting article about this, read “Solving the Calcium Conundrum” by Dr. Sprackland.

Vitamin and Calcium Supplements

Think of these as insurance. Their purpose is to make sure the tortoises get everything they need even if the food we offer may be lacking in something. 

Calcium Supplements are usually a form of either calcium carbonate (chalk), or calcium citrate. Calcium citrate is easier to absorb, but it is less concentrated so it takes twice as much to do the job. Avoid calcium
from bonemeal, oysters, or dolomite unless it is food-grade, since otherwise it can be contaminated with items such as heavy metals. Egg shells can be used, but contain a lot of grit and heavy metals. “Coral calcium” is OK but overpriced (it is just calcium carbonate and some sea salts). Better sources are food- or pet-grade cuttlebone, calcium sand (although some keepers feel this can clump and block the intestines), and foods containing bones, such as small fish or baby mice (use “fuzzies” when possible; “pinkies” do not have enough bone mass). You can also buy just plain calcium powder from health food stores, drug stores, or pet stores. Sometimes you can get it with vitamin D3 added.

Vitamin Supplements can be found in many forms including  pills, sprays, or ground up plants. Aim for a supplement that contains a variety of vitamins and minerals. Look for a supplement that offers the A, D, and E vitamins in ratios of about 100:10:1 or so to avoid overdoses.

Let the buyer beware! Recent reports have said that many animal and reptile vitamins do not contain what the label says – even some “big name” vitamin labels were found to be inaccurate – most often in regards to how much calcium is present. Some experts are recommending crushing human vitamins, which are more regulated, to ensure the proper nutrients.

Administer a small pinch per tortoise per week or so, more often if the diet is low in the nutrients. Sprinkle on food and lightly stir (so it does not look like mildew). Note: Because vitamins loose potency over time, replace them at least every year. More is not better! Too much stuff can cause problems of its own. Small doses used on occasion is a safe and helpful method. Check the Dosages and Guidelines page for more specifics.

The TORTOISE LIBRARY nutrient mix
There are several good supplements available, such as the excellent TNT (Total Nutrition for Tortoises), but you can make up an easy-to-use mix of fiber, calcium, and vitamins if you would rather not buy it.

  1. Chop or grind up dried, cubed, or pelleted hay (Timothy hay, etc.), until it is like dried parsley. The easiest way to break down the cubes is to tap them with a hammer and they will break apart into thin layers, then just crumple a layer up, tossing out any hard bits left over.
  2. Add about a heaping teaspoon of calcium powder per cup of hay flakes.
  3. Add about 1/8th teaspoon, or one crushed human vitamin tablet, to the mix.
  4. Toss or stir and store in an air-tight container.
  5. Serve by adding a pinch sprinkled over a meal one to three times a week, depending on how nutritious the meals are.

Revised 5-29-2012. (C) Mark Adkins