The US lab ranges go down to 200... and that is no longer considered safe. Significant neuro symptoms occur for people below 400.

I recommend the PNers stay over 1000.

There is no upper limit for toxicity for B12 assigned by research or the FDA. Some of us maintain over 2000.

The higher the blood level, the higher the level of B12 can get in the spinal fluid. The gradient between the blood and CSF is driven by concentration of the serum. So the higher the serum level, the more that crosses into the spinal cord and brain.
There have been some studies on low spinal fluid and MS and Fibromyalgia. So keeping good blood levels of a 1000 or more is
a good idea.
B12 in supplement form is best taken as methylcobalamin which is the active form. Orally one should take on an empty stomach since only about 1% may be absorbed. People with intact intrinsic factor may absorb a bit more, but most of a high dose of 1000-5000mcg is not absorbed passively. Presence of food will negate most absorption, since the food acts as a sponge and prevents the tiny microgram amounts from reaching the intestinal wall during transit.

MrsD, if some of these vitamins/minerals are best absorbed on an empty stomach, why does my multivitamin state that it should be taken with food? Just curious.

BTW this is the product I'm taking:

http://www.genuinehealth.com/multi-daily-joy.html

Because there is a general rule, in the vitamin "world" to take things with food to simulate "eating"

However, B12 is an exception. Its presence in the mixture if you take with food lessens its value since it will compete with the food for absorption. People with intact intrinsic factor will complex 2-4 micrograms the same as if it were derived from animal protein digestion. But the vast remaining amount of 1000mcg will not be absorbed most likely and will pass into the feces.

This rule I use is derived from research on thyroid hormone and digoxin which are given in microgram amounts orally as well. Studies show they are not absorbed with food, but are soaked up by the fibers and bulk of food going thru the intestine, and lost. Since B12 is the same dose, the rule applies to it. B12 is only absorbed in a small area of the small intestine. It is this fact...empty stomach or not, that has perpetuated the myth that B12 cannot be taken orally efficiently. It has only be recently that oral forms have been available in fact.

Many labels from supplement manufacturers contain erroneous information. One cannot trust them all therefore.

So if you choose to take the supplement mixture you have with food, the B12 may be wasted. The other things are less critical with this fact.
So if your goal is to increase B12 levels, you should take a separate stand alone B12 in addition --and do so correctly for best results.