Before commercial diets were available for crested geckos, the only option for feeding was either freshly blended fruits or baby food and insects. Because this lack of variety is not a healthy balanced diet, supplements were needed to make it so. However, guidelines on supplements are not exact and there was a risk for both undersupplementation and oversupplementation.
The dangers of under-supplementation in crested geckos are nutritional imbalances like Metabolic Bone Disease (MBD). Oversupplementation can cause problems such as Vitamin D3 toxicity. Additionally, too much calcium can cause trace deficiencies in other minerals.
Calcium is important not only for bone strength but also for proper body functionality. Most reptile supplements contain calcium but may not have all of the vitamins and minerals necessary for balanced nutrition.
Minerals and other nutrients interact with each other, which affects their bio-availability in the body. One of the most important interactions is between phosphorous and calcium levels. Phosphorous uses up equal amounts of calcium to be absorbed into the bloodstream. The amount of phosphorous injested needs to be “matched” with an equal amount of calcium, and if it’s not present in food at the same time, it can be pulled from the bones. With feeding and supplementing, be sure to add at least as much calcium to phosphorus. Be sure to get a supplement that doesn’t include additional phosphorus, as it is not usually missing from the unsupplemented diet for crested geckos.
Too much fat in the diet, whether from commercial foods using vegetable oils or animal fats from live prey, can also impede calcium absorption leading to MBD.
Vitamin D Toxicity
In the wild, animals synthesize vitamin D from sunlight: skin synthesis converts ultraviolet (UV) light into vitamin D3 (cholecalciferol).
The need for vitamin D varies between diurnal and nocturnal animals, and supplements are often offered with “low-d” or outdoor formulas and “high-d” or indoor formulas, the assumption being that reptiles housed outside need less vitamin D3 supplementation. Nocturnal animals such as crested geckos should be supplemented with around 4,000 IU/KG of vitamin d3. One gram of pure vitamin D3 is 40,000,000 International Units (IU), where one IU is equivalent to 0.025 μg (micrograms).
Excessive levels of supplemented vitamin D3 can be toxic and Hypervitaminosis D can lead to the excessive absorption and utilization of calcium (hypercalcemia). The use of cholecalciferol in rodenticides represents a significant hazard to other animals, causing systemic calcification of soft tissue, kidney failure, GI dysfunctions, cardiac abnormalities and hypertension.
Too much calcium (hypercalcemia) can act as a binder, inhibiting the absorption of essential vitamins and minerals. Since calcium neutralizes stomach acids, which inhibits overall digestion and assimilation of nutrients. Over-supplementation of calcium pushes the rest of the nutrients out of balance. Smaller amounts over time are better, optimally keeping the total amount of calcium in the diet at roughly 1.5%.
Luckily, there is a very easy way to ensure your crested gecko has everything they need without calculating calcium-to-phosphorous ratios or worrying about MBD or Vitamin D3 toxicity. Choosing a commercially prepared powdered diet for crested geckos takes all of the work out of providing a balanced meal for your pet. With or without the addition of live insect feeders, these diets take the worry out of feeding your crested gecko or other Rhacodactylus species.
Resources for Reptile Nutrition
Merck Veterinary Manual: Reptile Nutrition
Repashy Superfoods: Vitamins & Minerals Nutrition Article
Wikipedia: Vitamin D3 (Cholecalciferol)
Repashy Forums: How to Screw Up a Crested Gecko with a Bad Diet