Evidence of the Benefits of D3:
"Panther Chameleons, Furcifer pardalis, Behaviorally Regulate Optimal Exposure to UV Depending on Dietary Vitamin D3 Status"
Author(s): Kristopher B. Karsten, Gary W. Ferguson, Tai C. Chen, Michael F. Holick
Source: Physiological and Biochemical Zoology, Vol. 82, No. 3 (May/June 2009), pp. 218-225
"Effects of artificial ultraviolet light exposure on reproductive success of the female panther chameleon (Furcifer pardalis) in captivity"
Zoo biology [0733-3188] Ferguson yr: 2002 vol: 21 iss: 6 pg: 525 -537
"The Panther Chameleon: Color Variation, Natural History, Conservation, and Captive Management."
Ferguson G.W., J.B. Murphy, J.B. Ramanamanjato, and A.P. Raselimanana.
Krieger, Malabar, FL. 2004
Abstract from one: "Basking by ectothermic vertebrates is thought to have evolved for thermoregulation. However, another beneficial effect of sunlight exposure, specifically the ultraviolet B (UV-B) component, includes endogenous production of vitamin D(3). In the laboratory, panther chameleons exhibited a positive phototaxis to greater visible, ultraviolet A (UV-A) and UV-B light. However, with equivalent high irradiances of UV-A or UV-B, their response to UV-B was significantly greater than it was to UV-A. Exposure of in vitro skin patches of panther chameleons to high UV-B (90 microW/cm(2)) for 1 h significantly enhanced vitamin D(3) concentration. Voluntary exposure to higher UV-B irradiance (70 vs. 1 microW/cm(2)) resulted in greater circulating 25-hydroxyvitamin D(3) in female panther chameleons (604 vs. 92 ng/mL). Depending on dietary intake of vitamin D(3), chameleons adjusted their exposure time to UV-B irradiation as if regulating their endogenous production of this vital hormone. When dietary intake was low (1-3 IU/g), they exposed themselves to significantly more UV-producing light; when intake was high (9-129 IU/g), they exposed themselves to less. Vitamin D(3) photoregulation seems to be an important additional component of the function of basking."
"It has been previously shown that artificial UVB exposure of panther chameleons (Furcifer pardalis) enhanced hatching success, vitamin D status of adult females, and epidermal vitamin D production"
11. Ferguson GW, Jones JR, Gehrmann WH, Hammack SH, Talent LG, Hudson RD, Dierenfeld ES, Fitzpatrick MP, Frye FL, et al. Indoor husbandry of the panther chameleon (Furcifer pardalis): effects of dietary vitamins A and D and ultraviolet irradiation on pathology and life-history traits. Zoo Biol. 1996;15:279–99.
"Nutritional metabolic bone disease in juvenile veiled chameleons (Chamaeleo calyptratus) and its prevention."
Journal of Nutrition 140(11):1923-31, 2010 Nov
140(11):1923-31, 2010 Nov
It can be concluded that the indoor rearing of veiled chameleons fed with locusts gut-loaded with 12% Ca, dusted with vitamin A (250,000 IU/kg) (75 mg/kg) and cholecalciferol (25,000 IU/kg) (0.625 mg/kg) immediately before feeding, and provision of long (10 h/d), low irradiation exposure (3–120 mW/cm2 UVB) provided the best combination for the prevention of NMBD.
"Effects of vitamin D3 supplementation and UVb exposure on the growth and plasma concentration of vitamin D3 metabolites in juvenile bearded dragons"
This study shows that 2 h of UVb exposure enables adequate physiological concentrations of plasma vitamin D metabolites to bemaintained in growing bearded dragons. Oral supplementation of vitaminD3 is ineffective in raising plasma concentrations of 25(OH)D3 and 1,25(OH)2D3 to concentrations observed in UVb-exposed animals.
"THE REQUIREMENT FOR NATURAL SUNLIGHT TO PREVENT VITAMIN D DEFICIENCY IN IGUANIAN LIZARDS"
Author(s) :Christopher J. LaingB.V.Sc., B.Sc.(Vet.), Ph.D., Angelika Trube, Glenn M. SheaB.V.Sc., Ph.D., and David R. FraserB.V.Sc., Ph.D.
Journal of Zoo and Wildlife Medicine, 32(3):342-348. 2001.
11. Ferguson GW, Jones JR, Gehrmann WH, Hammack SH, Talent LG, Hudson RD, Dierenfeld ES, Fitzpatrick MP, Frye FL, et al. Indoor husbandry of the panther chameleon (Furcifer pardalis): effects of dietary vitamins A and D and ultraviolet irradiation on pathology and life-history traits. Zoo Biol. 1996;15:279–99.
12. Ferguson GW, Gehrmann WH, Karsten KB, Hammack SH, McRae M, Chen TC, Lung NP, Holick MF. Do panther chameleons bask to regulate endogenous vitamin D3 production? Physiol Biochem Zool. 2003;76:52–9.
13. Ferguson GW, Gehrmann WH, Chen TC, Holick MF. Vitamin D-content of the eggs of the panther chamaeleon Furcifer pardalis: its relationship to UVB exposure/vitamin D-conditions
Evidence of Toxicity of D3:
- In iguanas:
Hypervitaminosis D in Green Iguanas
-In chameleons: Indoor husbandry of the panther chameleon Chamaeleo [Furcifer] pardalis:
Effects of dietary vitamins A and D and ultraviolet irradiation on pathology and life-history traits
D3 is a fat soluble vitamin, which means that it builds up over time in organs such as the liver. It is not just eaten, used, and discarded. So it can build up to dangerous levels without anyone realizing it because you can't see it being stored. That is why the recommendation for supplementation is so infrequent.