If you have already caught the cold, here is a handy study to consider. It revealed that a few really large doses of vitamins A and D gave significant relief within 24 hours. How large? The A was 150,000 units and the D was a more moderate 15,000 to start. The next morning a third of this amount was given. The result, 82% of the test group was improved! ( 30.3% symptom free, and 51.8% almost symptom free)
Of course such a large dose of vitamin A is NOT to be taken for any length of time. But, used wisely this is a powerful health strategy.