Iguana Vitamin D3
How Vitamin D3 Works In Your Iguana
A major problem with keeping iguanas healthy in captivity, is supplying them with an appropriate supply of Vitamin D3. Vitamin D3 is a fat soluble vitamin (also known as cholecalciferol) that an iguana needs to assimilate the calcium in its diet. Without it, your iguana can contract a severe case of Metabolic Bone Disease.
There is no good source of this vitamin found within fruits and vegetables. It is also believed that iguanas can not absorb this vitamin through their food. So attempting to use a supplement is useless.
Wild iguanas manufacture their own vitamin D3 by basking in unfiltered sunlight. The ultraviolet radiation from the sun acts like a catalyst which converts a substance known as pro-vitamin D3 into pre-vitamin D3. In turn, this pre-vitamin D3 is converted into vitamin D3, which binds to a blood protein and then can be transferred to the liver via the bloodstream. This "activated" form of D3, then can be utilized to influence the metabolism of dietary calcium and phosphorus.
So how can you supply this crucial vitamin to your iguana? By purchasing the correct light. There are many "so called" reptile lights on the market. Many of them produce a spectrum of light known as UVA rays. Although UVA rays are good for increasing appetite, improving general fitness, and inducing reproductive behavior, they do not produce the vitamin D3. That can only be found in the rays referred to as UVB. The UVB rays found in the light you provide (or by access to one hour of unfiltered sunlight a day) are essential for the proper breakdown and utilization of calcium and phosphorus in your iguanas diet. Therefore, it should be considered a necessity when configuring your iguanas dietary needs.
D3 Cycle Diagram
 This amazing process begins when a cholesterol called pro vitamin D (7DHC) is produced in the animal’s skin (it is a natural process in humans too). When this cholesterol is exposed to natural light (including light in the UVB wavelength (290-315nm)), this cholesterol is turned in the skin membrane into pre vitamin D.
After exposure to warmth, this newly manufactured pre vitamin D is converted (in the skin membrane) into vitamin D3. It is essential to have this heating up period alongside UV radiation. Vitamin D3 is then sent out into the blood plasma and is bound with a vitamin D binding protein. This is then carried to the liver where this part of this vitamin is converted to a hormone called calcediol (25-hydroxy vitamin D3).
The blood carries this calcediol all around the body and into the kidneys where some of the hormone is turned into another hormone, called calcetriol. This compound then plays an essential role in calcium metabolism and controls the levels of calcium in the blood. Calcetriol also plays a huge role in the immune system and the cardiovascular system. It has been shown to lower the risk of cancers in the body and skin.
So we can see that exposure to natural sunlight is only the start of this amazing ability in reptiles and humans alike, to turn sunlight into life saving vitamins. This D3 cycle is dependent on the completion of the D3 cycle. If part of the cycle is missed out then the cycle cannot be completed properly. Changes and reactions would also be unable to be completed properly. This would result in an under provision of essential vitamins and hormones, and if supplementation were not used, a calcium crash could happen.
Author: Richard Brooks
1. Lighting For Crepuscular And Understory Reptiles © John Courteney-Smith
D3 Cycle Diagram - © Richard Brooks