Some sources advocate a high daily intake of Vitamin D to provide protection from viral infections, however a comparison of the rates or severity of Upper Respiratory Tract Infections between healthy adults with a very high intake of Vitamin D, and those with normal levels, fails to support these claims. Partly to blame is a strong Vitamin A D antagonism, where too much of one will inhibit the effectiveness of the other, so an excessive Vitamin D intake can worsen mucus congestion... Full Text