After I received a negative result (meaning, all's well) on a fasting 2-hour glucose test, I was puzzled. Not that I thought I had diabetes. But because the test did not confirm my findings, which were as follows.
When I eliminated all extra sugars from my diet (fruit juices, honey in my tea, sugar in my coffee, desserts, etc.), I found to my delight that my "cloudy head" as I called it, or foggy head, as others have noted, disappeared.
I had been dealing with this foggy head condition, ever since an unscrupulous endocrinologist overdosed me on thyroxin for a period of 8 years. During that time frame, my energy levels were so unreliable that I could no longer complete my (olympic) swimming pool laps. And when the glass-of-milk-to-give-me-energy did not work, I switched to McDonald's ice tea, hoping for that spurt of energy.
That didn't work either. So I chalked up the decline in energy to age. Without giving out fuller details of my downward spiral, I'll just say that from that point on, I began to increase the sugar levels in my diet, not excessively, but certainly more than what I had been used to. (I never had much of a sweet tooth, before.) And it was during this time that I noticed an increase in thirst, as well as the foggy head which affected my thinking.
Even when the overdose of thyroxin was discovered by a new family physician who actually read my lab reports, I continued my non-excessive sugar intake.
That is, until recently. How did I discover the solution to a now 15-year issue? Simply put, during an fecal occult blood test (FOBT), I forgot that I had to forego all vitamin C, even for 3 days prior to the test.
Since the approximately 2 cups of fresh (sweet) apple cider that I consumed daily contained this additive, I dropped this substance. With several days of cider withdrawal, I noticed to my surprise that I did not have as much of a foggy head. So I decided to extend my dietary rules to all extra sugars (not including the natural amount contained in a piece of fruit). Meaning, no more honey in my tea, rice krispy treats, etc.
Case solved. No more foggy head.
Now, it's important to note that long ago, I had to drop orange juice from my diet, OJ being high in oxalates, a substance I also had to control, due to compromises to yet another system. (Way to go, unscrupulous endocrinologist.)
A nephrologist to whom my family physician referred me, suggested that I squeeze lemon or lime juice in my water. Voilà the needed form of vitamin C, without resorting to oxalates (or excessive sugar). In sum, I became a "limey" 
. That is, I now had the needed daily vitamin C, except during the time frame required of the FOBT. Works like a charm.
I still don't know of the medical details of the foggy head. I only know that dropping all extraneous sugars worked in ridding me of this substandard way to live.
I'd be interested in knowing if it works for others. Btw, I don't know if the situation applies to one or more types of sugars -- I don't have enough training in nutrition to know or to properly test.
Post Edited (syd0211) : 11/26/2012 1:00:59 PM (GMT-7)