The Russian Tortoise 
Agrionemys horsfieldii ( Testudo horsfieldii)  

Calcium, Phosphorous and Vitamin D3

Bones require a specific ratio of calcium and phosphorous (in humans a ratio of 1:1 is ideal for absorption......most say 2:1 for bone growth). This is provided by diet and Vitamin D3 helps us use the calcium. Recent research shows that D3 is also very important for immune function and is of benefit in auto-immune disease and as a preventative measure for cancer (research abstracts available here). In the past, the focus has been on this ratio. And indeed too much phosphorous is a problem. The typical tortoise diet is abundant in phosphorous and low in calcium. This has been shown to be a major contributing factor in  Metabolic Bone Disease (MBD) and Pyramiding. The most common recommendation has been to dust all food with calcium carbonate powder. While on the surface this appears to be a logical solution, its flawed and can have serious health consequences.

Two other minerals play critical roles in calcium metabolism...magnesium and boron. Research shows these are very important in preventing osteoporosis in humans. Boron is only needed in trace amounts but is important. However a 2:1 ratio of calcium to magnesium is very important. In Humans research is showing that if magnesium levels are too low,  high amounts of calcium or vitamin D supplementation can lead to calcification of the soft tissues or to kidney stone formation. It is possible that prolonged high amounts of calcium (higher than a 2:1 calcium-phosphorus ratio) and supplemental vitamin D can lead to abnormal calcification of long bones in children or to hypercalcemia (high blood calcium levels) and soft tissue calcification in adults, as well as a decrease in bone strength. Recent research using leopard tortoise hatchling show this to be a real problem for tortoises as well.

To counter act this and to get the calcium/phosphorous ratio to a healthy 2:1 , its is often recommended to dust all food with calcium (usually calcium carbonate). While superficially it does seem to have benefit, it has its own problems. Too much calcium results in secondary deficiencies of zinc, copper and iodine, mal-absorption of essential fatty acids, and formation of calcium-containing bladder stones. Lack of calcium results in soft shells that often accompany pyramiding.

This research focuses on the hazards of over supplementing with calcium carbonate. It is generally known that too much calcium results in secondary deficiencies of zinc, copper and iodine, mal-absorption of essential fatty acids, and formation of calcium-containing bladder stones. However this recent research project tries to quantify the amount that is needed. Following is the abstract:

Vet Rec. 2005 Jun 25;156(26):831-5.
Influence of the calcium content of the diet offered to leopard tortoises
(Geochelone pardalis).
Fledelius B, Jorgensen GW, Jensen HE, Brimer L.

Laboratory of Toxicology, Department of Veterinary Pathobiology, Royal
Veterinary and Agricultural University, 9 Ridebanevej, dk-1870 Frederiksberg C,
Copenhagen, Denmark.

Twenty-four juvenile leopard tortoises were divided into four groups of six; one
group was fed a basic low-calcium feed for six months, and the other three
groups were fed the same basic diet supplemented with one, three and nine times
the amount of calcium recommended as a supplement to the diet of reptiles. The
animals' bone mineral content and bone mineral density were estimated by dual
energy x-ray absorptiometry, and blood samples were taken at the start and at
the conclusion of the study. One tortoise from each group was examined
postmortem. There was a clear depletion of calcium in the body of the tortoises
receiving no calcium supplement, and the shell of the tortoises receiving the
recommended calcium supplement did not calcify to the extent expected. The
tortoises that received three times the recommended calcium supplementation had
the highest growth rate and were thriving. However, metastatic calcifications
were observed postmortem in the two groups that were given the highest doses of

Publication Types:
Clinical Trial
Randomized Controlled Trial

PMID: 15980135 [PubMed - indexed for MEDLINE]


The main flaw of the paper is that the role of other minerals were overlooked. However a few important conclusions about supplementing are apparent. The most important is what happened to the over-supplemented group. The overall appearance was that it was a very healthy group of tortoises with excellent shell density. However on microscopic examination many of the organs and other tissues were being calcified. So while casual exam (the cornerstone for some breeders and experts is "'the eyes are clear, tongue is pink, stools firm and well formed, the tortoise is active and eating well so therefore its healthy" ) may show what appears to be a healthy tortoise, it is erroneous.

By far the best way to ensure a healthy tortoise is to feed a wide variety of high calcium foods. And if you must rely on grocery store greens pick the ones with the most bio-available calcium such as turnip greens and kale. Also supplement with powders such as plantain and dandelion. By relying on whole foods ((such as those found here) to supply the minerals, its very hard to have mineral imbalances and deficiencies. It is also virtually impossible to over supplement.

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Joseph E. Heinen BS, DC, FIAMA, Dipl. Ac. (IAMA)
copyright 2005,


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