Background and objective: Garlic has been widely used in clinical practice, and there were many systematic reviews (SRs) describing its effects. But none reviewed the clinical utility comprehensively, so we aimed to evaluate its effects from every aspect of its effects.
Methods: We comprehensively searched medical electronic databases, asked the experts in this field, along with reference tracking, and manual searching. We included all kinds of SRs, including Cochrane SRs and non-Cochrane SRs. Two authors independently selected articles for relevant SRs, and extracted data of included SRs, resolved differences by consultation with a third reviewer.
Results: We described nine SRs about garlic. Available evidence showed that garlic can reduce blood pressure (BP) in hypertensive patients and patients with elevated systolic BP (SBP), but not in normotensive subjects. Evidence about the effects of garlic on lipid parameters was contentious, so we cannot make a decision whether garlic is effective enough for reducing total cholesterol (TC), triglycerides (TAG), and high-density lipoprotein (HDL). As evidence was very limited and insufficient, relations between garlic intake and reduced risks of all kinds of cancers, antiglycemic and antithrombotic effects of garlic, the effects of garlic on cardiovascular morbidity and mortality were unclear. Garlic as a preventative or treatment option for the common cold or peripheral arterial occlusive disease or pre-eclampsia and its complications could not be recommended, as only one relatively small trial evaluated the effects separately.
Conclusions: Garlic might be effective in some areas of clinical practice, but the evidence levels were low, so further researches should be well designed using rigorous method to avoid potential biases.