There is a significant amount of anecdotal as well as published information showing that in some cases recommended B12 therapy simply isnt enough.
Another concern is when you say ample, exactly what are your levels? In the usa the low end of B12 accepted range is like 300 points lower than any other country in the world. There are countless cases of people being "within lab range" yet suffering greatly from B12 deficiency.
There are also many genetic factors that are involved which could possibly prevent normal B12 serum levels to actually get used properly, many times this can be partially overcome by simply adding more. And lastly, there is a theory where a past deficiency can create an increased need, a new low watermark if you will.
If your a person who likes getting labs done, to truly evalute B12 levels one would really need to get the following tests for an accurate assessment. When no B12 symptems arent present these just serum B12 is needed but in cases where symptoms exist, like chronic fatigue the only way to really rule out B12 is with the following:
Personally I found it cheaper to just take B12 for 6 months and see what impact it has.
I know 10mg seems like a lot but its water soluble and like many water soluble vits is extremely hard to take too much. B12 also isnt absorbed very well, of my 10mg recommendation you will only realize about 15% of it at best if taken sublingually, about 1% if swallowed.
My short list of supps in previous post are the cocktail (when a complete plan isnt in place that already includes these) put to use by Dr Hoffer for treating chronic fatigue and my own research indicates, for the reasons previously stated, that the underlying function these nutrients serve would benefit one with chronic fatigue.
If you havent already, google "phoenix rising B12" and spend some time reading the input from various users. One quickly finds that brands, especially for B12 are very important. I myself, out of the brands of B12 I have tried, have really only noticed any effects from source naturals brand, which coincides with the findings of many others.
For your Iodine test, was it a loading test or just a simple urine test? The loading test would give a much clearer picture as I understand it. The skin test I mentioned above isnt any good at showing the level of deficiency but its a very simple test to judge if Iodine is being absorbed. I highly doubt your body isnt absorbing iodine, but out of curiosity what are your T4, T3 and tsh levels? Was there any change after supplementing iondine/selenium?
So many symptoms that people have are the result of more than one deficiency I personally have come to think of trying to find the magic supplement as a total waste of time. Bodily functions often require a cocktail of nutrients and missing a few can throw off various processes leading to a variety of symptoms. Its nearly impossible to narrow it down to specific bodily process or supplement because so many symptoms have overlapping causes. The best approach is to worry less about finding and targeting a specific process and more about simply making sure to give the body everything it needs. Once a thorough and extensive supplement plan is in place and has been for a while (say 6 months) then you can reassess your symptoms and adjust doses accordingly if needed.
For magnesium I prefer magnesium citrate, there are also some decent blends on the market. Magnesium is one of the nutrients I have found where the brand isnt as important as for say B12.
And yes, I realize you came here asking about Iodine BUT I have found that quite often people are looking for a smoking gun, a cause, a supplement or two to target a specific bodily process and in doing so they have tunnel vision and it detracts from the big picture. Since our body is one organism and relies on a myriad of nutrients and we currently dont have an effective way to test them all so where is your issue and is it even iodine related?
If you want to know what nutrients play a role in iodine absorption get your reading glasses out because its going to take a lot of time and research. Tyrosine, sodium, selenium, iodine just for starters. But just about every essential nutrient plays a role at some stage weather it be in gut absorption, transportation, conversion or the creation and maintaining of the various tissues within the thyroid all the way down to the cellular level. After your done writing your doctoral thesis on the nutritional factors associated with iodine in the body, ask yourself, what have you learned? The short answer is essential nutrients are just that, essential! And you will likely be no closer to pinpointing your exact need.