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Calcium, Phosphorus and Vitamin D3 explained!

Posted: Thu Jul 11, 2013 3:48 am
by Lea
Vitamin D, Calcium and Phosphorus for Blue Tongue Skinks.

Both Calcium and Phosphorus are essential minerals and required by your skink for many biological processes. Getting the balance right in the diet is important for maintaining your skink's health.
Vitamin D is also required to support calcium uptake from the gut.


Calcium (Ca) the most abundant mineral in the body of vertebrate animals. It's required to maintain strong teeth and bones, where it is stored. It is essential for bone formation, blood coagulation, muscle contraction, nerve impulse transmission and heart health.
It's found in a variety of foods, in varying quantities, from meat to vegetable sources.


The main function of phosphorus (P) is in bone formation and teeth. It's also needed to help make protein for growth and in cell and tissue function and repair. It is also required for energy storage and metobolic processes.
As well as this, it works with the group of B vitamins to support kidney function, muscle contractions, maintaining regular heart rhythm and nerve conduction.
The main dietary sources are from protein groups, such as meats, as there is little found in fruits and veggies, however actual content varies considerably depending on how plants are grown. Generally, P levels in plants grown for human consumption are much higher than those found naturally, so charts showing relative values should be considered as a guide only.
Generally, deficiency is not an issue, but it can be a problem in excess, causing binding with calcium. This depletes the body of calcium, which causes bone problems in our skinks. This is referred to under an umbrella term of "metabolic bone disease"or MBD.

Vitamin D.

Vitamin D is actually a group of vitamins known as secosteriods. Probably the most important to note are Vitamin D2 and Vitamin D3. Vitamin D2 (ergocalciferol) performs roles in the body but is not specifically relevant for Calcium metabolism in reptiles.
Vitamin D3, however, is needed for bone health and enhances absorption of calcium from the gut. Low levels absorbed leads to low serum or blood calcium levels, which in turn, depletes calcium from the bones to try and maintain serum calcium normality.
This "stealing" of calcium from the bones makes the bones porous and brittle and is the main cause for MBD in lizards. MBD is a collective term for a range of bone abnormalities, such as osteodystrophy, secondary hyperparathyroidism and osteomalacia.
Osteodystrophy (bone malformation) and osteomalacia (sometimes referred to as rickets) are both caused by a Vitamin D deficiency and come under the collective term of MBD.

Why are they all important for blue tongue skinks?

Reptiles require the correct ratio in their diet to maintain biochemical processes and prevent MBD.
Vitamin D3 is required to help absorb calcium from the gut. For our skinks, the main sources for this are from the diet and from UV light, specifically UVB. UVB converts the basic form of inactive vitamin D to the active form by a series of processes in the body, involving the liver, kidneys and parathyroid glands.
For captive skinks, UV light alone may not be sufficient to support these functions, this is where supplementation becomes important.

How Much Calcium and Phosphorus do they need?

It is recommended that a ratio of 2:1 of calcium and phosphorus, respectively, is sufficient. So, approximately 2 parts calcium, to phosphorus. Along with Vitamin D3 in it's active form as a supplement, this should give sufficient quantities of each to maintain optimum health.

Or, if you think of it this way, one part calcium to one part phosphorus would not give any free calcium, since phosphorus binds readily with calcium and would result in calcium being "stolen" from the bones to maintain a healthy serum calcium. This would eventually lead to MBD. The stealing of bone Ca can also occur as a result of calcium binding with free oxalate, so therefore, the oxalate content of foods should also be considered.
As you can see, the more calcium freely available, the less likely it will be taken from the bones.

(Vitamin D3 in the active form can be easily provided by supplementing and this is readily available from reptile suppliers. Look for the active vitamin D3, as the inactive form will not be utilised and is lost through excretion)

A note about oxalates

Oxalate and its acid form oxalic acid, are organic acids which come primarily from the diet and is used commercially to remove rust from car radiators!

High oxalates in the urine and blood are associated with kidney stones, as they are often formed from calcium oxalate. When the calcium binds to the oxalate in the gut, it is excreted in the poop, but this can lead to a calcium deficiency.

However, when calcium is already low in the diet, oxalic acid is soluble and is readily absorbed from the gut into the bloodstream. If oxalic acid is very high in the blood being filtered by the kidney, it can combine with calcium to form crystals, resulting in kidney stones.

These crystals can also deposit in the joints and tissues, causing obstruction to movement, damage and pain. They can cause inflammation, even local infection.

So as well as calcium, vitamin D and phosphorus content, we need to be aware of foods high in oxalates, as not only can they lead to painful conditions, it can interfere with calcium absorption and lead to deficiencies, in spite of supplementation.

The Vitamin D Cycle and the Endocrine System

Now for a little science!


Low serum calcium is detected by the parathyroid glands and they secrete parathyroid hormone, PTh. This stimulates an enzyme in the kidneys (1-hydroxylase). It results in production of the active form of vitamin D3, also known as calcitriol.

Calcitriol helps by:

1. Activating the gut transportation of calcium
2. Increasing mobilisation of bone calcium to serum
3. Increasing reabsorption of calcium by the kidneys.

Simple, right?

Ok, well, maybe not, there is a lot to the science and I could write pages and pages and still be leaving bits out!
The main thing to draw from this though, is the importance and role of calcium, phosphorus and vitamin D3 in the prevention of MBD and bone health.

Getting the balance right is important, so taking a little time to understand the processes behind it help us better understand why diet helps us achieve optimum health for our skinks.


How and Hazewinkle. "Dietary dependence on calcium ... " Endocrinol Journal 1994, vol 96:12-18" onclick=";return false; - hypocalcaemia" onclick=";return false; - rickets
Field, Pollock and Harris. "The Renal System" 2001.

Re: Calcium, Phosphorus and Vitamin D3 explained!

Posted: Fri Jul 12, 2013 6:35 pm
by Toria Dawn
This is great information!!!! Thank you Lea! I have one question - the calcium+D3 supplement doesn't specify if the D3 is active or not. How can I tell, or would an active version say so clearly on the label?

Re: Calcium, Phosphorus and Vitamin D3 explained!

Posted: Fri Jul 12, 2013 8:36 pm
by Lea
The scientific name for the active form of vitamin D3 is 1, 25 dihydroxycholecalciferol but you may see it labelled as[/color] calcitriol

Somewhere on the labelling it should be identified as one of those, or say that it is "active". If you aren't sure, write down or photograph what you see and PM me and I can help you. Because UVB light is often given to reptile in their housing, some suppliers will supply vitamin D3 in the inactive form, expecting UV light to make it active. Although it will, we can not measure it's efficacy accurately and even when supplying UVB via bulbs, we may still fall far short of what is needed for adequate conversion.