Ninety days of consuming the garlic supplement also produced a 21% reduction in the number of symptoms of colds or flu, and reduced the number of work days missed due to illness by 58%, report researchers from the University of Florida.
The supplement was also found to enhance the function of immune cells, particularly NK (natural killer) cells and gamma-delta T cells, a group of immune cells found in large quantities in the gut.
“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,” wrote the researchers in Clinical Nutrition .
The study used aged garlic from Wakunaga of America, Inc and the California-based company co-funded the study along with the Agricultural Experiment Station at the University of Florida.
The common cold is one of the most widespread illnesses in the world. It is estimated that adults suffer from between two and four episodes annually, whilst children in school may have as many as 12 episodes per year.
A recent Cochrane review estimated that the total economic impact of cold-related work loss exceeds $20 billion per year. As a result, Americans spend around $2.9 billion on over-the-counter drugs (and another $400 million on prescription medicines) for symptomatic relief of cold.
The immune boosting powers of garlic are well accepted by consumers, and supplements are often sought because they offer the benefits of garlic without the odors that accompany the fresh bulb.
An aging process can convert odorous organosulfur compounds into water soluble compounds such as S-allyl-L-cysteine and S-allylmercaptocysteine, explained the University of Florida researchers.
Aged garlic extracts also contain compounds with potential to modulate the immune system, such as lectins, fructooligosaccharide, apigenin, and N(alpha) fructosyl arginine.
The researchers sought to establish if the aged extract could modify the immune cells, NK cells and gamma-delta T cells.
For their randomized, double-blind, placebo-controlled parallel intervention study they recruited 120 healthy subjects with an average age of 26 and randomly assigned them to receive daily supplement of the aged garlic extract (2.56 grams) or placebo for 90 days.
Results showed that the number of both types of immune cells increased more in the garlic group, compared with the placebo group.
Significant improvements were also reported for the number of symptoms of cold and flu, the number of days and incidences where people felt ‘under the weather’, and the number of missed days due to illness.
Commenting on the potential mechanisms, the researchers pointed to the various sulfur-containing compounds in the extract, including how these lead to increases in levels of glutathione in cells.
“Improved thiol status may be responsible for improvements in cellular proliferation and activation, resulting in reduced illness; however, more work is needed to show cause and effect,” they added.
The researchers also said that future work should elucidate which compounds in he aged garlic extract are responsible for the immune changes observed.
Source: Clinical Nutrition
Published online ahead of print, doi: 10.1016/j.clnu.2011.11.019
“Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: A randomized, double-blind, placebo-controlled nutrition intervention”
Authors: M.P. Nantz, C.A. Rowe, C.E. Muller, R.A. Creasy, J.M. Stanilka, S.S. Percival