After 90 days, compared to the placebo group, the garlic group had 21 percent fewer cold or flu symptoms and had missed 58 percent fewer days of work.
In the garlic group, researchers found higher levels of two kinds of immune-system white blood cells that intercept and kill invading bacteria and viruses. Doctors believe that sulfur compounds in garlic may reduce illness by raising cellular levels of the antioxidant glutathione.