Among the most widespread illnesses in the world, the common cold is estimated to be responsible for $20 billion per year in lost worker productivity.  Susan S. Percival , from the University of Florida (Florida, USA), and colleagues  enrolled 120 healthy subjects, average age 26 years, and randomly assigned each to receive either a daily supplement of aged garlic extract (2.56 g), or placebo, for 90 days. The team observed that the number of NK cells and gamma-delta T cells, two important types of immune cells, increased moreso in the garlic-supplemented group, as compared to those in the placebo group. As well, the numbers symptoms of cold and influenza were reduced by 21%, and the number of workdays missed due to illness was cut by 58%, among those who consumed the garlic extract. The study authors conclude that: "These results suggest that supplementation of the diet with aged garlic extract may enhance immune cell function and that this may be responsible, in part, for reduced severity of colds and flu.”