Supplementing the Sun!

One of the trickiest aspects of keeping reptiles is figuring out how we can best replicate their natural environment and diet inside a very unnatural enclosure.  Most ‘pet’ reptiles species originate from places that are warmer and sunnier than Minnesota, and certainly warmer and sunnier than the inside of our house! They also generally eat a wider range of foods (and seasonally changing selections) than we can offer in an enclosed environment.  This article will discuss how the Sun and Vitamin D work together to keep our reptiles healthy, and what we can do at home to replicate this relationship.  

Natural sunlight gives our lizards two major ingredients needed for calcium regulation; warmth and ultraviolet (UV) light.  Warmth and ultraviolet light help our lizards convert vitamin D precursors, and vitamin D in turn helps our lizards regulate their calcium levels.  Because in nature sunlight typically is providing both heat and UV light at the same time, it’s best to position our heat lamps and UV bulbs in the same part of the enclosure.  This allows our reptiles to bask in the ‘sun’ and get both their heat and UV needs fulfilled at the same time.  Conversely, the reptiles can reduce both heat and UV exposure by going to the other side of the enclosure.  Studies have shown that chameleons will actively seek out UV light to help increase their vitamin D levels if their diets are deficient, so this UV exposure in the cage is critical for regulation.  For our ‘full sun’ reptiles that are active during the day, such as a bearded dragon, uromastyx, and most turtles and tortoises, a strong 10% UVB bulb (also called a 10.0 UVB) is recommended (for larger species or enclosures, even more potent bulbs or multiple bulbs may be recommended).  What about crepuscular (morning/evening) or nocturnal species such as crested geckos and leopard geckos, who do not go out much during the day? Studies have shown even leopard geckos can increase their vitamin D with UV exposure, so it is recommended they have UV light as well, though often lower-power lights (2.5% or 5.0% (called 2.5 or 5.0 UVB)) are recommended to aid their self-regulation.  One theory is that these lizards are extremely efficient at utilizing UV light since they have such limited natural exposure, so a little bit can go a long way. There is some concern that too much UV light can cause eye problems for these ‘low sun’ species, so it’s important they have good hiding places for when they want to escape the rays.  

Note that though bulbs are generally labeled based on their UVB output, it is important to use bulbs that produce both UVB and UVA.  UV bulbs should be kept 12-18 inches from the surface of the enclosure where the animal sits, and should not have any glass or screens below them.  Make sure your animal cannot reach or touch the UV light.  Of course no artificial light can beat the beneficial effects of direct sun exposure, so it is good to take your basking reptiles outside during the summer on warm days for some direct rays (just make sure they don’t wander away!).  Research into optimal UV exposure for different species is always on-going, so recommendations may change over time.  

The UV and heat conversion of vitamin D precursors in the skin creates a compound called cholecalciferol, which is then processed by the liver and then kidneys to create active vitamin D3 (calcitriol).  Snakes, which evolved from burrowing species (‘fossorial’), receive all of their cholecalciferol through their diet of whole prey.  This generally eliminates their need for UV light to create their own vitamin D3.  Studies on snakes and UV exposure have shown varying results regarding vitamin D; in ball pythons a study showed no increase in vitamin D with UV exposure, however separate studies on corn snakes, eastern indigo snakes, and burmese pythons did show a positive increase.  There is also evidence that low levels of UV light can help snakes regulate normal activity and mating behaviors, so lower intensity (2.5 or 5.0 bulbs) are often recommended to promote natural behavior.  On the other hand, iguanas are thought to be unable to efficiently process cholecalciferol from their diet, and rely almost entirely on the UV and heat conversion process to form vitamin D3.  While the degree of reliance on UV light varies between species, just about every reptile benefits from some level of UV exposure.  

So we know that most (and maybe all) reptiles benefit from UV supplementation, but which reptiles require vitamin D3 supplementation in their diet? Snakes who eat whole prey can get all their necessary vitamin D from their meals, and do not need any additional supplementation.  Even though not all snakes can use UV light to make their own vitamin D, those whole prey are packed with all the vitamin D the snake needs! Most lizards benefit from vitamin D dusting to help supplement any lack of UV exposure they might have in their enclosure. As we just discussed, how much vitamin D they need will depend on how much UVB exposure they have and how much is in their diet already through natural sources.  Turtles and tortoises (chelonians) also benefit from supplementation, especially if they have insufficient UV lighting.  

Most vitamin D supplementation is given in conjunction with calcium or other vitamins in powdered form.  Vitamin D3 is the active ingredient on the label for a vitamin D supplement that can be used by reptiles.  A word of caution; there is a risk that we can over supplement vitamin D and cause toxicity, so be sure to talk to your vet about getting balanced supplements.  Vitamin D3 is even used in certain types of rodent poisons, so we need to be careful!  Again, our understanding of vitamin D requirements, like our understanding of UV, is always evolving as more research comes out, so recommendations may change in the future.  

-Dr. Cosimini

Evaluating the physiologic effects of short duration ultraviolet B radiation exposure in leopard geckos (Eublepharis macularius)

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Amelia Gould 1, Laure Molitor, Kelly Rockwell, Megan Watson, Mark A Mitchell

Do panther chameleons bask to regulate endogenous vitamin D3 production?

Physiol Biochem Zool. 2003 Jan-Feb;76(1):52-9.

Gary W Ferguson 1, William H Gehrmann, Kristopher B Karsten, Stephen H Hammack, Michele McRae, Tai C Chen, Nancy P Lung, Michael F Holick

Panther chameleons, Furcifer pardalis, behaviorally regulate optimal exposure to UV depending on dietary vitamin D3 status.

Physiol Biochem Zool. 2009 May-Jun;82(3):218-25.

Kristopher B Karsten 1, Gary W Ferguson, Tai C Chen, Michael F Holick

The effects of UV light on calcium metabolism in ball pythons (Python regius).

Vet Rec. October 2013;173(14):345.

J Hedley 1, K Eatwell

Effects of ultraviolet radiation on plasma 25-hydroxyvitamin D3 concentrations in corn snakes (Elaphe guttata)

Am J Vet Res. February 2008;69(2):294-7.

Mark J Acierno 1, Mark A Mitchell, Trevor T Zachariah, Marlana K Roundtree, Megan S. Kirchgessner, David Sanchez-Migallon Guzman