Make sure to provide Vitamin D3 either in the food or by having a basking area with a UV/IR source. Without Vitamin D3, the calcium cannot be used by the body. Mammals can convert Vitamin D2 from plants into Vitamin D3 but reptiles do not have this ability. Carnivorous reptile can find vitamin D3 in any prey’s liver. Insects and plants do not contain vitamin D3, so vegetarian reptile won’t benefit from it. Their only way to get vitamin D3 is to synthesize it themselves from Pro-vitamin D3 found in their skin. Pro-vitamin D3 will be converted into Pre-vitamin D3 thanks to UV-B. Pre-vitamin D3 will be converted into vitamin D3 thanks to IR. Vitamin D3 is responsible for maintaining a stable amount of calcium in the blood. If a lack of calcium in the blood is shown, the system will get it from the muscles, then from the bones. Hence, a lack of calcium can cause serious damage to your turtle.