A Further Myth Is Unleashed: UVB Does NOT Produce Vitamin D in Chameleons
Many reptile keepers assume that exposure to UVB light directly provides chameleons with vitamin D. However, this is a misconception—UVB does not create vitamin D from nothing; rather, it acts as a catalyst in an essential biochemical process.
When UVB photons penetrate the epidermis, they initiate a reaction with 7-dehydrocholesterol, a precursor molecule naturally present in the skin. This interaction converts 7-dehydrocholesterol into vitamin D3 (cholecalciferol), which is then transported to the liver and kidneys for further processing. In these organs, it is metabolized into its active form, calcitriol, which regulates calcium metabolism, bone health, and other physiological functions.
Thus, merely exposing a chameleon to UVB does not create vitamin D3 from scratch—this process relies entirely on the presence of precursor compounds, which must be supplied through diet and supplementation. Without proper nutrition, even the highest quality UVB exposure will not suffice.
Ensuring Proper Vitamin D Metabolism
For chameleons to maintain healthy vitamin D metabolism, they require a combination of factors:
Proper alimentation, including insect feeders enriched with calcium and vitamin D3 supplementation.
UVB exposure, ideally natural sunlight, but for indoor-kept chameleons, a linear UVB source (recommended T5HO 6% Arcadia UVB bulb) ensures adequate radiation levels.
Controlled environmental conditions, including optimal humidity, heat gradients, and stress reduction, to maintain metabolism efficiency.
Balanced calcium intake, as vitamin D plays a pivotal role in calcium absorption. Deficiencies can lead to Metabolic Bone Disease (MBD), a serious condition affecting bone density.
7-Dehydrocholesterol
Chemical Formula: C₂₇H₄₄O
Localisation: Found in the epidermal layers of the skin, mainly in the stratum basale and stratum spinosum, also present in mammalian milk and lanolin.
Synthesis: Produced from lathosterol by the enzyme lathosterol oxidase, as a precursor in cholesterol biosynthesis.
Function in Organism: Converts to previtamin D₃ upon UVB exposure, leading to cholecalciferol synthesis. Also functions as a precursor for ecdysone in insects, influencing molting. Deficiencies result in Smith-Lemli-Opitz syndrome, affecting cholesterol metabolism.
D3 Cholecalciferol
Chemical Formula: C₂₇H₄₄O
Localisation: Found in skin, liver, and kidneys; obtained from animal-based foods such as fish, liver, eggs, and dairy.
Synthesis: Formed from 7-dehydrocholesterol in skin under UVB radiation, then converted in the liver to calcifediol and finally calcitriol in the kidneys.
Function in Organism: Vital for calcium homeostasis and bone health. Ensures proper calcium absorption in the intestines. Used medically for rickets, osteoporosis, and vitamin D deficiency. Excess intake leads to hypercalcemia, causing kidney stones and cardiovascular complications.
Calcitriol
Chemical Formula: C₂₇H₄₄O₃
Localisation: Synthesized in the kidneys and circulates in blood plasma, binding to vitamin D receptors (VDR)in target tissues.
Synthesis: Derived from calcifediol (25-hydroxyvitamin D₃) through hydroxylation in kidney cells by the enzyme 1α-hydroxylase.
Function in Organism: Regulates calcium and phosphate metabolism, ensuring bone mineralization. Modulates immune function and influences gene expression via VDR binding. Used clinically for hypocalcemia, chronic kidney disease, and osteoporosis. Excess levels lead to hypercalcemia, causing nausea, muscle weakness, and kidney dysfunction.