Makes sense to me. If people already intake their RDA through a regular diet, they need to bump up the dosage to detect the effect of, well, additional dosage. Unless the 90 mg of vitamin C is meant as an additional intake on top of what we already get from our diet, which wouldn’t really make sense. They needed to decide on a number, so they picked 1,000 mg. They had to pick something, right? And if many of macgyver’s patients take 2,000 mg, the 1,000 mg they decided to go with sounds reasonable to me.