What about your calcium? I mentioned if you are a slow oxidizer with high calcium you will feel better on C. If not then that is probably why the intolerance though some say it's a sign of gut malabsorption which there could be some truth to it.
My calcium is a bit low, definitely not high. My HTMA makes me a fast oxidizer which would explain why I can't take vitamin C. Still I think vitamin C would fix some of my issues.
Some people don't take to l-ascorbic acid well because they have issues with their digestive system - stomach and gut. Cathcart says l-ascorbic acid intake is the preferred way, and if irritates the stomach/gut, those issues have to be resolved. L-ascorbic acid is more acidic that the buffered ascorbates, of which sodium ascorbate and calcium ascorbate (Ester-C) are the most common. Many people use these ascorbates in place of l-ascorbic acid, and they do well. But still, gut issues have to be looked at resolved.
From what I've gathered in going thru the Vitamin C foundation forum, Hickey (a professor) believes that ascorbic acid is absorbed thru the stomach, and what is left over that goes to the duodenum, is neutralized by bicarbonates coming from the pancreas. If there is some ascorbic acid left after the neutralization at the duodenum, it goes to the colon. The colon will react to the acidity by flushing it with water, and this is what we experience with the bowel flush. My personal conclusion, and it's just a guess, is that the body's need for vitamin C is expressed largely through the stomach lining's absorptive capacity for vitamin C, and what it can no longer absorb is left to be neutralized in a limited way in the duodenum, and the ascorbic acid that remains and goes to the colon is flushed. If the stomach is central to ascorbic acid absorption, then it requires the stomach to be healthy and fully functional, and a large of its functionality has to do with the ability to produce enough acid for digestion. In the case of ascorbic acid, the stomach has to have enough acidity, as it should, to render the ascorbic acid easily absorbable through the stomach lining.
I seem to have more issues with sodium ascorbate than vitamin C powder from natural sources. I have just ordered ascorbyl palmitate so I can try this form. But yeah maybe it's a gut issue.