A 2005 study by researchers at the Federal Research Centre of Nutrition and Food (Germany) found that those men and women who took daily vitamins and minerals with probiotics (bacteria that can activate the immune system, particularly T-cells) for at least three months reported reported reduced cold symptoms than those suffered by people who took only vitamins and minerals.  The men and women taking a combination of vitamins, minerals, and probiotics experienced:

• Colds that lasted almost two days less (than an average otherwise of nine days)

• Less time with a fever, reduced to 6 hours (rather than the average otherwise of 24 hours)

• Less severe headaches, coughing, and sneezing

Probiotic bacteria, in the form of Lactobacillus and Bifidobacterium strains, are found in respectable amounts in yogurt.  They are also available, in higher doses, in dietary supplement form (freeze-dried powders, capsules and wafers are preferable over liquid supplements, which are highly perishable).  Look for probiotic supplements with the highest "colony forming units" per dose.   Because bacteria counts drop as the product ages, mind the expiration date.  Take probiotic supplements on an empty stomach.

"In the course of a year, people in the United States suffer 1 billion colds."  ~ U.S. National Institute of Allergy and Infectious Diseases