Ultra violet light. What we know and what we don't know.

Ultra violet light, unseen by us humans, is necessary for most reptiles in order to create the vitamin D they need for healthy bones and a good immune system. Too much of it can cause skin and eye damage. Too little or none of it can cause a lack of vitamin D which in turn produces a vital hormone that regulates bone health and also the immune response.
Many reptile keepers who don't have UV light try to get round the need for it by dietary supplement of vitamin D or by feeding food that contains vitamin D, such as whole mice and rats. But we still don't know how much UV light most reptiles need. Sometimes a UV light is put into the vivarium and lights up the whole of it so the animal cannot escape exposure to it.
Yet in the wild reptiles regulate their exposure to UV light. In the same way they regulate their body warmth by basking. They will bask inUV as long as they need and then shelter from it. Therefore captive reptiles must be given a hiding place, or the UV light must be applied in such a way that they can move from a "hot" UV spot to a "cooler" UV spot.
Most reptile keepers have caught on to the fact that there must be a temperature gradient within the reptile enclosure, so that the animal can choose whether to be in a hot spot or a cool spot. Now we need to provide them with a UV light gradient too.  The heat lamp and the UV lamp should not be combined. A reptile should not have to choose to get too much UV light in order to get heat, or visa versa.
Gary Fergus and colleague decided they would try to work out how much UV light a reptile needed by looking at the animals in the wild and seeing how long they spent exposed to it. It was not easy.
They concluded that keepers of captive reptiles should provide a UV light gradient from maximum to minimum (by providing a refuge). That care should be taken not to produce vitamin D overose by too much supplementary dietary vitamin D.
So far so good. But they highlighted the lack of exact knowledge.
1. How long does each species of reptile in the wild expose itself to UV light?
2. How much vitamin D does the diet of wild reptiles provide?
3. What is the natural circulating level of vitamin D in a wild reptile?
4. How far can the reptile regulate its access to UV light according to its level of vitamin D in the body? ie. does it "know" when its vitamin D levels are low and does it therefore spend more time in UV light?
5. How sensitive is the reptile skin of different species to the absorption of UV light and conversion into vitamin D?
6. What is the ideal level of vitamin D for each species of reptile?
We don't know.

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Gary W. Ferguson,1 Andrew M. Brinker,1 William H. Gehrmann,1 Stacey E. Bucklin,1 Frances M. Baines,2 and Steve J. Mackin (2010) Voluntary Exposure of Some Western-Hemisphere Snake and Lizard Species to Ultraviolet-B Radiation in the Field: How Much Ultraviolet-B Should a Lizard or Snake Receive in Captivity?' Zoo Biology 29, 317-334.

Ultraviolet light - your lizard needs it for communicating..... don't keep it in the dark

RobinSings. https://en.wikipedia.org/wiki/Puerto_Rican_crested_anole

Lizards can see colours that we see and they can see colours we don't see - the colours in ultraviolet light. And colours matter to them, because they communicate with each other using colour signals. If they couldn't see ultra violet colour, it would like being colour blind for a human. And worse, because where we use words, they use colour to "speak."
Anoline lizards, arboreal American lizards, use their dewlaps to communicate.  They open and close them, making a sort of colour flash, rather like (but not very like) light signals used in morse code from ships. The brightness of the colours and how they stand out from the background makes them effective signals. Male lizards sit up on a high perch or branch, and flash their dewlaps to attract females and deter male rivals from a distance. Dewlaps are coloured differently in different species, probably to make sure that they show up in different habitats.
The females and rival males "capture" the signals with their eyes which have special cones. One type of cone is specialised for ultraviolet light. (Humans don't have this kind of cone.) Scientists tested Puerto Rican crested anoles to see what happened if there was no ultraviolet light visible. The lack of ultraviolet meant that the signal looked less bright to the lizard. The signal (which simulated a dewlap flash) just looked dark against the background.
Moreover, ultraviolet light helped the lizard detect motion. A dewlap flash is only a flash if it stops and starts, so detecting motion is important. Detecting motion in all animals, including humans, seems to depend on the contrast between signal and background which is more noticeable for a lizard sees the ultraviolet light.
So if we are keeping lizards in vivariums with no ultraviolet light - or where the UV lighting has failed - we are keeping them in the dark. Not only are they not getting the UV light they need for vitamin D (which means low immune system and poor bones), but they are living in a dull dark world where they cannot communicate properly.

For more read:  Fleishman, L. JJ. & Persons, M., (2001), 'The influence of stimulus and background colour on visisbility in the lizard, Anolis cristatellus, The Journal of Experimental Biology, 204l 1559-1575

Too much or too little vitamin D for reptiles? What do we know so far?

Some lizards may use basking not just for heat but for UV light.

By now most reptile keepers realise that too little vitamin D is bad for reptiles. Vitamin D is either absorbed through natural light or through the diet. Although carnivorous reptiles can get vitamin D in their diet: strictly herbivorous reptiles will not get enough just from diet. And it now looks as if relying on diet along, even in carnivores snakes, risks vitamin D inadequacy.
What do low levels of vitamin D do? Vitamin D is important for the growth and development of bones, for the immune system, artery and vein health, and reproduction. So low levels will impact badly on all these functions. We now know for sure that good vitamin D levels are important for the successful reproduction of several captive reptile species.
Vitamin D can be found in supplements that are given to reptiles. But there is a downside to this. It looks as if dietary vitamin D can lead to too high a vitamin D level if supplements are used incorrectly. In reptiles with an overdose of vitamin D, the aorta gets furred up with minerals.  So supplementing vitamin D by diet can be tricky.
Vitamin D levels are also affected by ultra violet light. But there have been no reports yet of vitamin D overdosing because of UV light. Yes, there can be skin damage from "too much" UV light but not vitamin D overdose. There seems to be a mechanism in the skin hat prevents overdose.
So.....
It is safer to use UV lighting or access to natural daylight to give your reptile enough vitamin D. The animal can probably regulate its vitamin D levels to prevent overdose.
Moreover, some (probably not all) carnivorous captive reptiles that get their vitamin D from a diet of mice etc. may well benefit from UV lighting as well. Carnivorous Komodo dragons get more vitamin D from UV light than dietary vitamin supplement. Conversely ball pythons were able to get their vitamin D equally well from either.
What is the take-home message from this? Use of dietary supplements may not be enough and risks overdose if used incorrectly. UVB light on its own will not lead to overdose and is therefore safer. Some reptiles will benefit it even though they get vitamin D from a carnivorous diet.
AND MOST IMPORTANT OF ALL - Keep up with modern developments. This is an area which is still being researched. What was best practice ten years ago is not best practice now. If you think you know it all, you probably don't.

To read more about this go to:

Watson et al (2014), 'Vitamin D and ultraviolet B radiation considerations for exotic pets,'Journal of Exotic Pet Medicine, 23, 369-379.

 

How iguanas need their vitamin D - from light or a supplement?

There are two ways to get vitamin D - eat it or absorb it through the skin from light. Does it matter which? In the wild green iguanas would regulate their body temperature and their vitamin D by basking in the sun (an ultra violet light source) then going to the shade (without ultra violet light) when too hot. As they are herbivores they cannot get the vitamin from their food.
In 2004 a study suggested that dietary supplements of vitamin D were a good source rather than UV light. The problem with UV light then was that a reliable source of light was then not available.
You will find the details of the study here - http://www.anapsid.org/pdf/jody-hibma-uvb.pdf
In l996, a more complicated study was set up. This time different lighting was used and some of the iguanas showed very high levels of vitamin D, if they were given both a dietary supplement and an UV light. Strangely, though, these high levels didn't seem to poison them - though igs have been known to die of vitamin D overdose. Read the full account here - http://www.anapsid.org?iguana/bernard-d3.html.
So do iguanas need UV light and dietary supplements. They certainly need UV light and when you do put in UV light, you must give the iguana a place in the shade where it can escape the light if it chooses. It will regulate its temperature so the UV light needs to be in the same place as the heat lamp. If it is not the lizard will spend most of its time in the heat lamp area and miss the benefits of UV lighting.
Do they need a vitamin supplement as well? This seems to be doubtful. A lot of the general reptile supplements on the market will do them no good and may do harm. Again, read up on the topic here - http://www.anapsid.org/vitamin.html
It's difficult. It's complicated. And we don't know as much as we should. All this means that a green iguana is a pet for the experienced reptile person, not for a beginner.