A systematic review on the influence of trial quality on the effect of garlic on blood pressure.

BACKGROUND: Garlic is a widely used herbal product for hypertension. Previous meta-analyses on the effect of garlic on blood pressure (BP) have been contradictory however. We hypothesised that methodological deficiencies may have contributed to this disagreement. We therefore evaluated whether trials reporting on the effect of garlic on BP had sufficient methodological qualities and a proper description of BP determination. METHODS: MEDLINE , EMBASE, AMED, the COCHRANE library, IBIDS and CINA HL were systematically searched for trials reporting on the effect of garlic on BP. Both the methodological quality and the quality of blood pressure measurement were appraised using predefined quality scores. RESULTS: 32 Studies were identified. Of these studies, 13 were included previously by other meta-analyses. The methodological quality of the studies was poor. Only four trials had adequate allocation concealment, no single trial reported an intention-to-treat analysis and blinding of the evaluators was done in three trials only. Moreover, half of the studies did not report any data on BP measurement. No trials reported on the arm level. Body position was described most often. All trials fulfilling a predefined cutoff point were conducted in normotensive subjects. CONCLUSION: The effect of garlic on blood pressure cannot be ascertained. Previous meta-analyses have been based on trials with inadequate study designs, methodological deficiencies and with too little information about blood pressure measurement. In our view, use of garlic cannot be recommended as antihypertensive advice for hypertensive patients in daily practice