Many garlic supplements are heavily marketed as a treatment of infections.
But are they really effective?
To answer this question, we clearly need clinical trials.
The aim of this RCT was to examine the impact of garlic tablets on nosocomial infections in hospitalized patients in intensive care units. It was carried out on 94 patients, admitted to the intensive care units in Kashani and Al-Zahra hospitals. Patients were randomised into case and control groups. The case group administered one 400 mg garlic tablet (Garlic tablets 400 mg, Gol Darou Company) daily for 6 days and the control group received placebo. During the study, inflammatory blood factors and infection occurrence in the two groups were compared. During the study period, 78 intravenous catheter tips were sent to laboratory for culture of which 37 cases were in the intervention group and 41 in the control group. Culture results of Catheter tips was positive in 5 cases all of which were in the control group. Frequency distribution of catheter tip culture was significantly higher in the control group than that of the intervention group. The authors concluded that garlic supplementation has shown to be effective in patients admitted to ICU, who are highly susceptible to nosocomial infection, and it can be used for the prevention of septicemia and urinary tract infections. However, further research with larger sample size is needed.
The trouble is not just that this trial was less than rigorous, but that there are so very few similar investigations to confirm or refute the anti-infectious activities of garlic.
In this study, healthy human participants (n = 120), between 21 and 50 y of age, were recruited for a randomized, double-blind, placebo-controlled parallel-intervention study to consume 2.56 g aged garlic extract (AGE)/d or placebo supplements for 90 d during the cold and flu season. Peripheral blood mononuclear cells were isolated before and after consumption, and γδ-T and NK cell function was assessed by flow cytometry. The effect on cold and flu symptoms was determined by using daily diary records of self-reported illnesses. After 45 d of AGE consumption, γδ-T and NK cells proliferated better and were more activated than cells from the placebo group. After 90 d, although the number of illnesses was not significantly different, the AGE group showed reduced cold and flu severity, with a reduction in the number of symptoms, the number of days participants functioned suboptimally, and the number of work/school days missed. The authors concluded that AGE supplementation may enhance immune cell function and may be partly responsible for the reduced severity of colds and flu reported. The results also suggest that the immune system functions well with AGE supplementation, perhaps with less accompanying inflammation.
There is plenty of in vitro evidence to suggest that garlic and its compounds have anti-bacterial, anti-viral and anti-fungal effects. Yet, for a range of reasons, this may not translate into clinical effects. To find out, we need clinical trials. So far, such investigations were almost entirely missing.
The two recent studies above are, I think, a good start. They are far from perfect but their findings are nevertheless mildly encouraging. For once, I do agree with the standard conclusion in alternative medicine:
More and better clinical trials are justified.