Researchers from Poland and Italy looked at studies published in the English language from 1970 to 2017 that explored how botanical ingredients and phytochemicals may affect cognitive declines.
"As it emerges from this systematic review, the use of some phytochemicals and botanicals seems to be very promising in order to delay the onset and progression of neurodegenerative and other age-related diseases," according to their report, published in the April edition of Pharmacological Research .
Their goal was to summarize and comment on the available evidence supporting the use of some botanicals and phytochemicals in clinical practice.
Looking at randomized clinical trials and meta-analyses
The researchers used two databases--Medline and the Cochrane Register of Controlled Trials--to collect reports from a time period of 47 years.
They used the terms "botanicals," "dietary supplements," "herbal drug," "nutraceuticals," "phytochemical," "cognitive impairment," "Alzheimer's disease," "clinical trial," and "humans" to narrow down the results.
"A number of studies have investigated the possible action on cognitive decline of different botanicals and phytochemicals, most of which are well-known anti-inflammatory or antioxidant agents with a good tolerability and safety profile," they wrote.
The search focused on seven botanicals and phytochemicals that have a body of science demonstrating activity on the central nervous system and other clinically-relevant effects in modulating cognitive decline in humans.
They looked at Ginkgo biloba, Vitis vinifera, Cammelia sinesis, Theobroma Cacao, Bacopa monnieri, Crocus sativus, and Curcuma longa. Here's a summary of some of the phytochemicals and botanicals they explored:
The researchers found that most of the randomized controlled trials available used the EGb761 Ginkgo biloba extract. "Ginkgo biloba is one of the most widely used natural compounds for the prevention and treatment of Alzheimer's disease," they reported.
They cited a 2016 meta-analysis of 21 clinical trials by researchers in China , which reported that Ginkgo biloba supplementation in combination with conventional medicine was superior to conventional medicine alone in improving mild cognitive impairment scores.
Eleven studies on Ginkgo biloba total were cited from their database search. They concluded that Ginkgo biloba is "potentially beneficial for the improvement of cognitive function, daily life activities, and global clinical assessment in patients [who had] just suffered from mild cognitive impairment."
The researchers found that most of the randomized controlled trials available used the EGb761 Ginkgo biloba extract, according to the researchers.
Resveratrol (Vitis vinifera)
Most studies analyzed by the researchers used trans- isomer resveratrol, found naturally in berry skins of most grape cultivars. They cited 34 studies that looked at resveratrol's potential cognitive benefits.
"Cognitive deficits were demonstrated to correlate with higher reactive oxygen (ROS) levels and nitrogen species: in effect, the oxidative stress seems to precede the senile plaques formation. In this regard, resveratrol exerts potent antioxidant activity that could be useful in preventing neurodegeneration in Alzheimer's disease," they reported.
"In the recent years, a great attention has been given to the potential positive cognitive effects of flavanols contained in Theobroma cacao," according to the researchers, referring to cacao beans by its scientific nomenclature.
The research they cited suggest that cocoa flavanols affect both endothelial vascular function and insulin sensitivity through mechanisms involving nitrous oxide.
"Short-term interventions with flavanol-rich cocoa in elderly volunteers reported improvements in cerebral blood flow and neurovascular coupling," they wrote.
In another cited study, published in the British Journal of Clinical Pharmacology in 2013, researchers formulated two drinks containing cacao flavanols, one with a high dose (494 mg) and another was low (23 mg).
They measured arterial cerebral blood flow using arterial spin labelling functional magnetic resonance imaging before and after drinking.
"Significant increases in regional perfusion across the brain were recorded following consumption of the high flavanol drink relative to the low flavanol one, in particular in the anterior cingulate cortex and the central opercular cortex of the parietal lobe," the researchers reported.
"In the opinion of the authors this could be associated to improvement in cognitive performance."