Another factor to keep in mind when taking oral vitamin C is dosing frequency.

Dr. Steve Hickey, who wrote the book Ascorbate, has shown that if you take vitamin C frequently throughout the day, you can achieve much higher plasma levels. So even though your kidneys will tend to rapidly excrete the vitamin C, by taking it every hour or two, you can maintain a much higher plasma level than if you just dose it once a day (unless you're taking an extended release form of vitamin C).

There are also a number of people, primarily with the naturopathic perspective, who believe that in order to be truly effective, ascorbic acid alone is not enough -- you need the combination of the ascorbic acid with its associated micronutrients, such as bioflavonoids and other components.