In a majority of patients affected by sinus congestion and sinus headaches, cellular tests show Vitamin C and nickel levels to be considerably below normal. Vitamin A stores show below normal as well, which in itself is a common cause for bronchial or sinus mucus congestion. When supplementing Vitamin A, females of child-bearing age should not ingest amounts larger than 3000 IU day because of its potential to induce birth defects in the fetus. Excessive intake of Vitamin A can also cause headaches! Since iodine helps to thin reduce mucus, it would be worthwhile to check its status, and one's thyroid function also... Full Text