All I can do is tell you what I do and how long my chameleons live, etc.
For veiled chameleons, I dust the insects with a phosphorous-free calcium powder on most feedings. Most feeder insects we use have a poor ratio of calcium to phos. and this helps to make up for it.
I dust with a vitamin powder twice a month that contains a beta carotene source of vitamin A. There is controversy over whether chameleons can convert beta carotene to vitamin A so some give a little vitamin A once in a while. Preformed vitamin A can build up (beta carotene can's) in the system and excess can prevent the D3 from doing its job and lead to MBD.
I dust with a phos.-free calcium/D3 powder twice a month because my chameleons only get UVB from tube lights. D3 from SUPPLEMENTS can also build up in the system and cause problems, so don't overdo it.
I gutload my crickets and feed them a nutritious diet...greens (dandelion, collards, endive, kale, escarole, mustard greens, etc.) and veggies (carrots, squash, sweet red pepper, zucchini, sweet potato, white potato, etc.)
Appropriate temperature is important to allow good digestion.
UVB light (that does not pass through glass or plastic) either from the sunlight or UVB tube lights allows the chameleon to produce D3 to use the calcium in its diet.
Keeping my chameleons the way I do, most females live to be 6 years old and the males even older. Babies that I have raised do well too.