Immunity boosting vitamins includes Beta glucans which are one of the most widely studied and effective natural substances for supporting balanced immune function. They are naturally found in foods such as baker's yeast, mushrooms and cereal grains like barley, oats, rye, and wheat. Vitamin D3, Vitamins C and E, and zinc, all contribute to the protection of cells from oxidative stress caused by free radical damage. Free radicals cause damage to your body and can add stress on the immune system.