Moderator: ofonorow
OxC wrote:A simple list of facts:
- Reduced ascorbate is transported into cells, through the cell membrane, by SVCTs.
DHAA, formed when reduced ascorbate is oxidized, is transported into cells, through the cell membrane, by certain GLUTs. Dietary sources of reduced ascorbate include ascorbic acid (found naturally in foods, also in many dietary supplements), sodium ascorbate, calcium ascorbate, magnesium ascorbate (these salts are found in some dietary supplements, such as "buffered" vitamin C preparations), and even compounds such as ascorbyl palmitate (a fat-soluble compound added to some processed foods as a preservative, but when ingested the palmityl residue can be cleaved by esterase enzymes in the gut, releasing an ascorbate ion, and thus becoming a dietary source of vitamin C). There are others. Dietary sources of DHAA include the DHAA found naturally in food, DHAA that is formed when the ascorbate in food becomes oxidized during processing or even chewing food, DHAA that is found in trace amounts in almost all dietary supplements (it is essentially impossible to have a large quantity of ascorbate that is not accompanied by a trace amount of DHAA due to some oxidation of the ascorbate), DHAA that is found in significant quantity in one brand of dietary supplement, and now, as demonstrated in the video http://youtu.be/YHKBhz7OCB4 DHAA that can be found in megadose quantities in a specially-prepared zucchini smoothie.
When ingested, reduced ascorbate is absorbed and appears in the bloodstream at a particular rate; generally the peak value in the bloodstream occurs about 2 - 3 hours after ingesting it in typical supplemental or megadose quantities.
It is clear that the more you eat in a single dose, the higher the peak blood values can get. But it is also clear that after consuming a dose of somewhere around 200 mg, absorption from the gut slows tremendously, and it requires multi-gram increases in dose to only slightly increase the resulting peak blood levels. This phenomenon is currently attributed to characteristics of the SVCT transporters.
When ingested, DHAA is absorbed and appears in the bloodstream (as reduced ascorbate) more quickly than when reduced ascorbate itself is ingested.
The peak levels occurs somewhere around 30 to 90 minutes after ingestion. The peak blood level achieved by ingesting 5 grams DHAA was twice as high as the peak level achieved by the same individual when he ingested 5 grams of reduced ascorbate. More rapid uptake and higher intracellular levels from exposing cells to DHAA as opposed to reduced ascorbate has been demonstrated in many in vitro studies. This phenomenon is currently attributed to characteristics of the GLUT transporters.
Here's some speculation:
- The term "bioavailable" is usually defined (in reference to vitamin C) as the amount of an oral dose that appears in the bloodstream, as compared to the same amount infused directly into the bloodstream. Blood levels are monitored over time to produce curves, and area-under-the-curve analyses are used to compare the estimated total amount of vitamin C in the blood from a single dose given orally versus the same dose given IV. The value is stated as a percent. When 200 mg reduced ascorbate is given orally, such calculations show that this dose is almost 100% bioavailable. When larger doses are given orally (say, 2 grams) such calculations show that this size dose is maybe only 20% bioavailable. The rapid and extremely high blood values achieved by ingesting DHAA suggest that the oral bioavailability of DHAA is much greater, although I'm not aware of any such calculations ever being done. Nevertheless, I speculate that doses of DHAA of 1 or 2 grams, or even 5 grams or more, may be very close to 100% bioavailable.
I'm not sure there is any evidence to support an assumption that "probably 20%" of a 200 gram dose of AA is converted to DHAA, but maybe it is true. Maybe, for that matter, the conversion of AA to DHAA is responsible for most of the perceived benefits of taking megadoses of AA. As you have pointed out, there remains a great deal that is unknown as to the fate or function of large doses of AA.ofonorow wrote:A forum poster wrote an article published in the Townsend Letter providing evidence that it is DHAA that is ultimately responsible for ascorbate's anti-viral properties. (At these 200,000 mg levels, probably 20% breaks down to DHAA and that may be what creates much of the benefit).
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