I take them even when not fasting.My reasoning is as follows: If you take a reasonable dose, your body will just eliminate the excess. If you have a persistent deficit, you can have serious medical problems, and since it take months for these things to appear (and to be corrected), when you notice it is too late.
I take a basic multivitamin from costco, vitamin D, calcium and fish oil. When fasting, I add folic acid, magnesium (twice a day) and electrolytes capsules.