Studies have proven that ordinary low dosage vitamin C will not stop a cold. The right dosage will at the onset. As soon as the tickle or clear nasal drip starts, take 8000 mg every 20 minutes for the first two or three hours.

And remember that in the northern latitudes in Winter, the Sun is too low in the sky for the UV/B radiation to penetrate which creates vitamin D on the skin. With sufficient vitamin D and C supplements, one can easily defeat colds.