Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Musings on D3 and UV...

©1996, 2002 Melissa Kaplan


Every time I pick up a reptile magazine and look at the ads, or read posts on the Internet and electronic mailing lists, there seems to be some new product hitting the market making questionable, if not downright ridiculous or dangerous, claims.

The most recent group of products is particularly insidious. Spray-on-food vitamins, "solar" and "nocturnal" D3 drops, and very high output ultraviolet fluorescents are among the ones that concern me. (It should be noted that the same maker of these drops, being marketed as the ideal replacement for exposure to sunlight and UVB wavelengths, recently bragged to an iguana owner that their secret ingredient in their frozen Iguana Flower frozen "food" product is Welch's Grape Jelly. And they want to be taken seriously...)

Although there have recently been more studies than ever before done on reptile physiology, nutrition, and response to ultraviolet and vitamins, they still don't hold a candle to what has been done in the pet mammal area. What is particularly worrisome is those independent studies, completed by reptile veterinarians, reptile nutritionists, and biologists, that are resulting in findings contrary to the claims made by the manufacturers of the vitamin and lighting products.

For example, a popular reptile multivitamin, Nekton-Rep, was found in independent study (Donoghue and Langenberg, in Mader) to not contain four of the minerals listed on the "guaranteed analysis" label. One of those four minerals was (are you sitting down?) calcium! Susan Donoghue, a reptile vet/nutrition researcher, analyzed several reptile, dog, and general animal vitamins, and Centrum, a human multivitamin. She found all the reptile vitamins to be lacking in many minerals and trace elements. She recommends the use of a mammal or general pet multivitamin instead, or Centrum, a vitamin that has all trace elements, vitamins and minerals represented. In addition, she believes, based on empirical evidence gained through her own reptile practice and formal feeding studies, and the practices of other reptile vets, that no vitamin, reptile or otherwise, contains enough calcium for reptiles, especially for herbivorous reptiles.

One thing neither she nor any other researcher, private or pet product manufacturer, has done, however, is to determine the exact amount of each vitamin, mineral and trace element that is required each day to maintain, in conjunction with proper environment and diet, optimum health, for each species, or even generalized to a family or class. So, the claims of vitamin product manufactures whose packaging and ads state they provide exactly the amount the reptiles need are meaningless. The Four Paws representative I spoke to did nothing to convince me that this product was worthwhile; when I voiced my concerns with it, she huffed up and snidely replied "Well! People will buy anything that has a picture of their animal on it, whether it is any good for them or not."

The spray-on-food vitamins, at least, are not as harmful as the spray-on-animal vitamins. Reptile skin is designed to keep body fluids inside the reptile's body. This is one of the key differences between reptiles and amphibians. Amphibians have highly permeable skin that not only ties them to life in water or highly humid places, but also puts them at risk for injury, illness or death from so many substances. Rather than being stopped by the barrier of the skin, substances permeate through the amphibian skin cells, reaching the interior of the body. When reptiles evolved from amphibians some 250 million years ago, their impermeable skins meant they could adapt to life on land and away from water and high humidity. So, spraying an oily substance laced with vitamins is not going to do a thing to supplement their diet! Neither will spray-on moisturizers do anything for them - but, like the spray-on-reptile vitamins, they do enormously well lining the pet store's and product manufacturer's pockets.

Spray-on-food vitamins at least will get into the digestive tract. But are you giving them enough with each spray? As noted reptile vet Douglas Mader stated in an article a couple of years ago, anyone who claims to know the exact amount a reptile needs is lying. You are paying a lot of money for a plastic spray bottle, water, flavoring, and a little bit of vitamin. A better value for your money would be a good dry multivitamin product that you mix in with the reptile's food. (Centrum, and even human calcium carbonate tablets may be crushed to a powder and the powder added to the food.)

Vitamin D3
My article on Metabolic Bone Disease goes into the natural development of D3 in the body as a result of the previtamin D formed through exposure of the skin to ultraviolet B wavelengths, so I won't repeat it here. If you are unfamiliar with the process, or the numerous disorders clustered under the MBD umbrella term, please read that article.

D3 is formed naturally in the body through exposure to UVB wavelengths (290-320 namometer, or nm). These wavelengths are produced by the sun, but are filtered out by regular glass and plastic; even fine-mesh screen can filter out significant amounts. (The windows in our house block out the UV wavelengths - otherwise all fabrics within range of the window would fade out within just a few years. Glass used in constructing commercial aquariums/terrariums is also made from plain window glass.) Thus an animal needs to be exposed to direct sunlight. It doesn't take much for an organism to get the amount of UV needed to metabolize adequate amounts of D3 when (again, this bears repeating), the environment and diet are right. Human needs are satisfied by 45 minutes exposure to the sun a week. Reptile veterinarian and researcher Dr. Alison Alberts states that 30 minutes exposure to the sun a day is sufficient for green iguanas.

Carnivorous and omnivorous animals get D3 not only by their body manufacturing it through exposure to sunlight (even nocturnal snakes come out at dusk to bask a bit), but through eating healthy prey. Prey that is not healthy, prey that is fed a marginal diet or one lacking in proper nutrition, or is composed of old or sick animals, will result in malnutrition, including adversely impacting the predator's ability to properly metabolize and process the nutrients its digestive system extracted from the prey.

Plants, however, do not contain D3, cholecalciferol. Plants contain D2, ergocalciferol. Ergocalciferol has been found to be much less efficient in calcium metabolism than cholecalciferol. Herbivorous reptiles maintained on plant diets who are not given adequate amounts of UVB were found to develop MBD. Since no one knows how much D3 an herbivorous reptile needs, it can be a dangerous proposition to rely on supplementing D3 through use of oral vitamins. How much is enough? How much is too much? Unfortunately, more is not better. Too much D3 causes the same thing as not enough D3 - metabolic bone disease. How then can we assure that our herbivores and omnivores are getting adequate D3, but not too much?

The UVB Connection
As discussed above, UVB interacts with the skin to form previtamin D. This is then converted in the body, through the function of several organs, into D3. Thus herbivores are able to manufacture their own D3.

We herbivorous reptile keepers have a little problem in captivity. Many of our reptiles come from hundreds or thousands of miles away. Central American iguanas and tortoises kept in Scotland or Korea, for example, do not live in an area that gets the same amount of natural UVB that they would get living in their native habitat. James Ball's article on lighting contains a chart of the amount of UVB that hits the earth at a variety of latitudes and longitudes, with the amount hitting the equator at noon given for comparison. What Ball and other researchers have acknowledged, however, is that no one has measured exactly how much UVB the species who live in these areas actually get every day or even in aggregate over a period of time. It is one thing to say that "X amount of UVB hits the equator at noon." It is quite another, however, to say that, ergo, "every equatorial reptile needs to get X amount of UVB every day."

First off, it isn't noon all day long at the equator. Just as it does where we live, the sun rises in the east and sets in the west. During the sun's passage (well, okay, the earth's revolution around the sun!), the sun's light (the infrared, visible, and ultraviolet wavelengths) passes through the earth's atmosphere at an oblique angle, both as it rises towards midday and as it starts to set in mid-afternoon. This naturally filters out much of the intensity, the quantity, of the infrared (which produce heat) and ultraviolet wavelengths, with visible light growing and diminishing in the early morning and late afternoon accordingly.

UVB-Producing Fluorescent Lights
One of the big arguments against using low UVB-output fluorescents such as Duro-Test's Vita-Lite (True-lite is the name under which it is sold in the ECM) is that it doesn't produce the same amount of UVB as produced at the equator at noon. Well, sunlight doesn't produce the same amount of UVB at any other time of day, nor at any non-equatorial place, as it does at noon! The question, I believe is incorrect. Instead of asking "Does this UVB-producing fluorescent produce the same amount of UVB as produced by the sun at the equator at noon?", what we should be asking is "Does this light, in conjunction with my paying attention to the temperatures, photoperiod, stress levels and diet of my reptiles, prevent the onset of MBD?" For my, in my experience keeping a number of lizards and chelonians, the answer to the latter question is "Yes, it does."

A wild reptile, unless it has an anatomical/physiological abnormality or injury that prevents normal functioning of organs and systems, doesn't overdose on UVB in the wild. A study of captive iguanas, however, at the National Zoo, found that when they were kept under experimental very high output (VHO) UVB fluorescents, they developed a condition that, the researchers said, would, in mammals, be considered vitamin D toxicity - too much D. What concerns me greatly is the recent appearance on the market of UVB fluorescents, Reptile-D lights, which claim to produce 8% UVB (though physicists would argue with the method by which the 8% was derived). Observant readers of ads or packaging will have noted that the verbiage on the packaging and ads states "not intended for human use." Why? Because it has been determined that anything over 5% is dangerous to humans - eye disorders and skin cancer being the main concerns. As we have found with so many things, more is not necessarily better. If a low-output UVB producing light such as the 3% light made by Zoo Med, or the even lower output Vita-Lite, produce enough UV when used properly (no farther than 18 inches from the reptile, replaced every 6-12 months), why risk overexposure? (It is interesting to note that the makers of the Reptile-D 8% light have recently come out with a 3% light, despite their heavy marketing the over the past year that claimed their lights were so much better for our reptiles than all the other UVB producing lights. Why, I wonder? Perhaps because they realized that consumers out there were beginning to be worried about the "not for human use" warnings and so not buying their they were not getting the market share away from Zoo Med and Durotest they had hoped? Coming out with a competing 3% light certainly helps solve that little problem...)

There appears at this point to be more research the use of oral and injectible D3 and the use of UVB in iguanas, the world's largest herbivorous lizard, than there has been with tortoises, most species of whom are also completely herbivorous. A.C. Highfield did do some studies, however, using UVB-producing lights. Both groups were fed identical diets. One group got only a little UV lighting, a D3 supplement, and calcium supplement. The other group got more UV and only a calcium supplement. Both groups did fine - until the UV output of the tube used in the second group began to degrade. Once it was replaced, and a little D3 added to their diet, the softening shell hardened again. Unfortunately, since D3 was added as well as the bulb replaced, it is unknown from this study whether the UV light alone would have made a difference. From what I have seen and experience myself, however, I believe that it would have.

Personal Experience with UVB
I got a 9 month old captive bred and hatched Vietnamese leaf turtle (Geomyda spengleri) from the breeder. I set him up in an enclosure complete with a 15" Vita-Lite installed into an under-cabinet fluorescent fixture set on top of the screen top of the enclosure (the light itself was less than 12 inches above the turtle). His diet consisted of redworms (rinsed, blotted and dredged in a calcium supplement that contained D3), and snails gut-loaded on high calcium greens. After 3 months, I noticed that his shell was softening. I had the housing set up and was feeding him exactly as did the breeder, yet clearly he was getting calcium deficient. While I sat looking at him one day, it suddenly hit me: when I installed the Vita-Lite into the fixture, I then put the the plastic diffuser that came with the fixture back over the tube. Installed in a kitchen, this diffuser would reduce the glare of the light, providing an easy-on-the-human-eye diffused light. This same diffuser, however, also blocked the UVB wavelengths. With insufficient UVB, the turtle was unable to manufacture enough D3 (and was not getting enough from his supplemented prey to make up the difference) to metabolize enough calcium. Thus, calcium was not being replaced into his shell and, presumably, his bones.

I removed the plastic diffuser from the fixture, and put the fixture back on the enclosure, where it sits at the same 12 inches above the turtle. I did not increase his calcium supplement, nor did I add any more D3, nor did I increase the length of time every day that his Vita-Lite is on. Within 2 weeks, there was a noticeable difference in his shell; within another week, his shell was firm again and there have been no further incidents of softening. I also make sure to replace the bulb every 12 months.

What astounds me in the above incident is not that the diffuser blocked the UVB - I know that it does that. The astounding part is not only did I manage to forget that little fact, but that it had happened to me before!

A couple of years ago, I bought some compact Vita-Lites to try. Like non-UVB producing compact fluorescents, these plug into a ballast which in turn is designed to screw into an incandescent light fixture. I got them to try them to see if they would be a suitable replacement for the long Vita-Lite tubes. Three of us were using them for iguanas. In each case, MBD developed. In each case, we were using the plastic diffusers that came with the compact lights. I found, however, that removing the diffuser didn't correct the MBD for the large iguanas. Without changing the diet, the vitamin supplementation, nor the amount of time each day exposed to the light (which was within 6 inches of the iguanas), I corrected the problem by exposing the iguanas instead to a regular, straight Vita-Lite tube. Thus, not only is it direct access to the ultraviolet wavelengths that is necessary, it is also how much of the body is exposed. A compact UVB producing fluorescent just doesn't produce enough UVB over wide enough area to be effective for 3-4+ feet of lizard. Given that the skin of a chelonian is presented only at the most extreme ends, I wouldn't use a compact UVB-producing fluorescent for them either, unless they were very small hatchlings, out of fear that not enough of their skin would be exposed to the wavelengths.

I regularly encounter people who seem to be raising healthy lizards and chelonians without benefit of UVB or sunlight. But the fact is that metabolic bone disease is still one of the the most common illnesses/disorders found by reptile veterinarians. To me, and many of the reptile veterinarians who write about chelonian and lizard care in captivity, it just makes sense to provide both UVB, either sun or artificial produced UVB, and a properly constructed and supplemented diet.

The Other Ultraviolet
Most discussions of ultraviolet wavelengths address UVB. There is, however, another segment in the ultraviolet spectrum that is also critically important. UVA (320-400 NM) is the range in which reptiles, and many other animals, can see. What looks like a faintly red-orange anole dewlap to us is a bright, fiery red beacon to another anole. That pretty blue tongue in a blue-tongue skink's mouth is bright fluorescent pink to another blue-tongue skink. Reptiles also have more color receptors in their eyes and so are able to better discriminate colors than are humans.

While all senses play an important role to reptiles, vision is probably one of the most versatile. The wavelengths they are able to perceive play roles in color perception which in turn affects appetite. Reds are redder, greens greener, yellows yellower. Transformed, then, is the rather bland, largely monotonous pile of greens, vegetables and fruits. For a reluctant feeder, the presence or absence of UVA may mean the difference between feeding, weight gain and growth, or malnutrition (due to chronic starvation) and stunted development.

Natural behaviors, too, may be stimulated by UVA. From thermoregulatory triggers that tell the reptile when to bask, feed, and find a sleeping spot for the night, to cues triggering onset of hormonal changes that kick off the breeding season, to tracking and identifying conspecifics in the environment (much like way a dog can learn about an interloper from smelling urine, many reptiles leave - and can read - UV sensitive trails or markers in their environment). Denying reptiles UVA would be like going through life with only one eye. You could certainly see and function, but you would be missing much of the depth and complexity of your environment. To a reptile, that depth and complexity makes up for the lack of spoken communication and, in many cases, very limited stereo (binocular) vision. To deny them UVA is to reduce their ability to effectively interact with their environment and with other animals in their environment, which in turn leads to chronic low levels of stress.

Stress, Malnutrition and Vitamin Disorders
Too many people who understand that a lousy diet, stressed-out lifestyle, long days, and too little sleep take a toll on the body that popping vitamin supplements won't correct, nonetheless act as if they believe that providing an inadequate environment and marginal diet can be remedied by loading their reptile with vitamins. Just as it won't work in humans, it won't work in reptiles. This, combined with the fact that we just don't know what exactly each species' vitamin and mineral requirements are on a daily basis, means that we need to act both conservatively to ensure we don't overdose them, but to also ensure that they are given the best opportunity to let natural systems go to work to keep them in balance.

Many of the reptiles in captivity are wild-caught. Even captive bred animals are subject to stress, some more than others. It is increasingly being found in many species, including reptiles, that chronic low levels of stress may have long lasting impacts, especially on the immune system. Chronic immune stress results in decreased immune response, thus impairing the organism's ability to fight off infection. As is being found with many human disorders, stress also leads to the reduction or increase of many different hormones, including natural cancer and infection fighters. As we are seeing more reptiles being kept for longer periods of time in captivity, we are starting to see more diseases and disorders that may be related to long term chronic stress.

No matter how hard we try, when we keep a nonnative species, we are at best only approximating its environment. Try as we may to replicate the temperatures, photoperiod, and topography, we can rarely replicate diet or even the nutritional make-up of their diets. The plants that herbivorous reptiles eat in the wild just aren't found in the produce section of our markets. As for nonnative species, not only are complete plant inventories often nonexistent on a species-by-species basis, we have no hope of ever obtaining those plants and growing them ourselves. So, at best, we must try to provide a proper diet made up of foods known to be safe, for which we can do some rough computations of their protein, fiber, and vitamin content, and for which we make ourselves aware of phytocompounds that may adversely affect our herbivores' and, to a lesser extent, omnivores' health - plants that adversely affect calcium metabolism and thyroid function are the two most commonly encountered. (See Highfield's Dietary Considerations article, and the feeding and foods section of my Iguana Care, Feeding and Socialization document for discussions of these plants.) For our omnivores and carnivores, we must be sure to feed health prey. "You are what you eat" is true when it comes to our reptiles. As with being unable to feed our herbivores native plant species, we are also generally unable to feed our predators natural prey - prey that their species would feed on in the wild. We don't know what minute but cumulative effects on them that this has. We do know that feeding old, unhealthy, oversized or heavily chitinous prey does pose health risks. So just as we must try to construct a proper plant based diet for our herbivores, we must strive to provide a healthy variety of healthy vertebrates and invertebrates to our omnivores and carnivores.

What we can do--what we must do--is to make sure we give our reptiles the best possible chance to be as healthy as possible. Doing so will mean that their internal systems will function properly, or as properly as it can in what is still an alien environment. The best way to do this is not only by meeting their environmental (physical and psychosocial) needs, but by providing additional tools, in the form of both multivitamin (which contain D3) and calcium supplements - and UVB wavelengths, either through regular exposure to the sun or 10-12 hours a day exposure to UVB-producing fluorescents (placed no further than 18" from the animal and replaced at least annually).


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Alderton, David. (1992) Turtles and Tortoises of the World. Facts on File Publ., New York.

Allen, M.E., Oftedal, O.T., Baer, D.J., and Werner, D.I. (1989) Nutritional studies with the green iguana. In, Proceedings of the Eighth Dr. Scholl Conference on Nutrition of Captive Wild Animals, pp. 73-81. Lincoln Zoological Gardens, Chicago, IL.

Ball, J.C. (1995) A Comparison of the UV-B Irradiance of Low-Intensity, Full-Spectrum Lamps With Natural Sunlight. Bulletin of the Chicago Herpetological Society, 30(4):69-71.

Bernard, J.S., OT Oftendal, et al. (1991.) The response of vitamin D deficient green iguanas (Iguana iguana) to artificial ultraviolet light. Proc Am Vet 1991:147-150.

Bernard, J.S., Oftedal O.T., Ullrey, D.E. Idiosyncrasies of Vitamin D Metabolism in the Green Iguana (Iguana iguana). Proceedings, Comparative Nutrition Society Symposium, pp. 11-14

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Warwick, C. (1990) Reptilian ethology in captivity: Observations of some problems and an evaluation of their ætiology. Applied Animal Behaviour Science, 26, pp. 1-13.

_____ (1990) Important ethological and other considerations of the study and maintenance of reptiles in captivity. Applied Animal Behaviour Science, 27, pp. 363-366.

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New research:
UV-lamps for terrariums: Their spectral characteristics and efficiency in promoting vitamin D3 synthesis by UVB irradiation

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