This is why we perhaps should be careful in using high vitamin C dosing. It says C reduces excess cortisol. Meaning healthy people who do actually secrete cortisol and produce lots during stressful situations. Some of us might have low output and wouldn't want to take anything which lowers it further, although I understand some vitamin C is necessary for the adrenals to be able to make cortisol at all:
http://answers.google.com/answers/threadview?id=252375