In order for your uromastyx to have healthy bones, it needs three things -- calcium and vitamin D3, and the ability to digest it! Unless you live in the desert and can give your uro an outdoor enclosure, you’ll need to “create” these things artificially. Other than food, which has already been discussed, you’ll need a vitamin supplement and a “sun” – a combination of incandescent and fluorescent lighting. This is because reptiles are cold-blooded and cannot generate their own body heat, which is needed in order to be able to digest food.
There are two different types of lighting that you’ll need to make your “sun.” One is incandescent bulbs and the other is fluorescent bulbs. Incandescent bulbs are the ones that look like the lightbulbs that you put in your lamps at home. They generate only heat and light. Fluorescent bulbs are the long ones that generate very little heat, but give off light and are capable of emitting UV radiation. And heat + light + UV radiation = our fake sun. Keep in mind that not all fluorescent lights give off UV rays, so you must buy the ones that are produced specifically for reptiles. ZooMed’sReptisun 5.0 (a brand name) is ideal for the needs of uromastyx. Both are easy to find at pet stores that carry reptile supplies.
Next, is the vitamin supplements. Rep-Cal (another brand name) makes the vitamins that are ideal for your uro’s needs. First, you’ll want Calcium with vitamin D3, whose name implies exactly what it is, and second, you’ll want Herptivite, a multivitamin. Both of these come in powdered form, so all you need to do is lightly sprinkle them over your uro’s food. As a general rule of thumb, I use the calcium every couple of meals, while I use Herptivite about once per week.
Now here’s how it all works... Calcium is needed for healthy bones. Vitamin D3 is needed in order to absorb the calcium from food. UVB rays from fluorescent bulbs are needed in order to make use of the vitamin D3. And heat from incandescent bulbs is needed in order to produce the body heat needed to digest. So think of it this way: incandescent lighting + UV fluorescent lighting + vitamin supplements + food = healthy bones. It's a chain – none of them can work well without the others. And that’s how it works.
And for a final note of warning... What happens if you don’t include these things? It can lead to Metabolic Bone Disease, which will turn your lizard into a cripple and eventually kill him/her. Plus, other health problems can and will occur. Not a very pleasant thing.