Cognition enhancing effect of rosemary (Rosmarinus officinalis L.) in lab animal studies: a systematic review and meta-analysis

Patients with mild cognitive impairment eventually progress to Alzheimer's disease (AD) causing a strong impact on public health. Rosmarinus officinalis has long been known as the herb of remembrance and can be a potential cognition enhancer for AD. The aim of this review was to summarize the qualitative and quantitative aspects of R. officinalis and its active constituents in enhancing cognition. A structured search was conducted on Google Scholar and PubMed to find relevant studies that assessed the effect of R. officinalis extract or any of its active constituents on cognitive performance in animals. The following information was extracted from each study: 1) article information; 2) characteristics of study animals; 3) type of intervention: type, dose, duration, and frequency of administration of R. officinalis; and 4) type of outcome measure. Data were analyzed using Review Manager and meta-analysis was performed by computing the standardized mean difference. Twenty-three studies were selected for qualitative analysis and fifteen for meta-analysis. From the fifteen included papers, 22 with 35 comparisons were meta-analyzed. Effect sizes for intact and cognitively impaired animals were 1.19 (0.74, 1.64) and 0.57 (0.19, 0.96), indicating a positive effect on both groups. The subgroup analyses showed substantial unexplained heterogeneity among studies. Overall, R. officinalis improved cognitive outcomes in normal and impaired animals, and results were robust across species, type of extract, treatment duration, and type of memory. However, studies had a considerable amount of heterogeneity, and subgroup analyses failed to find any heterogeneity moderator.