Alot is dependent on the person.

The liver stores excess B12 up to 5 yrs, that we know of. Not everyone will have that long storage..but some do.

The reason I think it is important to stay over 1000, is the transport into the CSF (cerebrospinal fluid). B12 moves into the spinal cord and brain this way...involving a gradient from high (blood serum) to low (brain + spinal cord)... A person on TBI once posted a paper on this movement, and I wish I had copied it, but I didn't.

So the higher the serum the better the movement into the central nervous system. We know from recent studies that MS and Fibro patients show lower than normal B12 in the CSF taken by lumbar punctures. And also Dr. Snow in his very important paper had patients who he thought were fairly normal in levels, who did better on supplement ANYWAY. These were few compared to the total number, but still had neuro symptoms at fairly mid range B12 levels. So his take was to give the supplements anyway. I have that paper linked on the B12 thread. I think it is post #70.

So it will vary from person to person. But expect some B12 to be stored in the liver, and also to move into the CNS and out of the serum. After months of highs, that you feel better finally and stabilized there, you can drop to 1000mcg a day orally.

There also may be other factors... low D.... impaired B1 metabolism, etc. So once there is no change with B12, you need to look at other things too. Some PN tingling etc is paresthesia...a symptom of some imbalance. PN is a disease of nerves.(with damage). So separating that out is dicey and you have to be patient with those thoughts. Keep a journal, as that may help. Things like MSG in food will definitely cause neuro symptoms in some people. Glutamate and aspartate (Nutrasweet) are big culprits! Watch for those food intolerances ..that come from nightshades, etc.