Appropriate temperatures allow for proper digestion and thus play a part indirectly in nutrient absorption.
Basking temperatures should be in the low 80'sF for a veiled female.
Exposure to UVB allows the chameleon to produce the D3 it needs to use the calcium in its system.
D3 from supplements can build up in the system and lead to health issues while D3 from exposure to UVB won't likely build up as long as the chameleon can move in and out of the UVB when it wants to.
Since most feeder insects have a poor ratio of calcium to phosphorous its important to dust the insects just before feeding them to the chameleon with a phosphorous-free calcium powder at most feedings to help make up for it.
To ensure that the chameleon gets some D3 without overdosing it and leaving the chameleon to produce the rest of the D3 from its exposure to the UVB light we recommend that you dust twice a month with a phosphorous -free calcium/D3 powder.
It's also recommended that you dust twice a month with a vitamin powder that contains a beta carotene (prOformed) source of vitamin A. PrOformed sources of vitamin A cannot build up in the system and lead to overdoses like prEformed sources can and will leave it up to you to decide whether the chameleon needs prEformed or not.
It's important to feed/gutload the insects properly too. Crickets, locusts, superworms, roaches can be fed / gutloaded with greens such as collards, escarole, endive, dandelion greens, kale, etc and veggies such as carrots, sweet red pepper, squash, zucchini, sweet potato, etc.
