Green tea, white tea, and black tea are made from dried leaves of Camellia sinensis, a perennial evergreen shrub. Up to 40% of the dry weight of tea leaves is accounted for by antioxidants called catechins; epigallocatechin gallate (EGCG) is the most abundant catechin found in green tea. While several clinical trials have been carried out, no long-term studies have evaluated whether EGCG alone can protect from cognitive decline or dementia. EGCG supplements are considered safe for most people at commonly used doses, but high doses may affect liver function.
While some studies have tested the effects of EGCG in several disease populations, no studies have evaluated whether EGCG alone may slow cognitive decline or prevent dementia in healthy adults. Our search identified:
• 7 double-blind randomized clinical trials testing EGCG alone or combined with other compounds/interventions • 1 pilot clinical study in people with Down syndrome • Numerous preclinical studies
Two small trials suggest that EGCG treatment may very modestly improve memory functions, inhibitory control, and adaptive behavior in people with Down syndrome, though this protective effect was evident in only 3 out of 24 cognitive tests [1; 2]. Two clinical trials in multiple scerlosis have reported that long-term EGCG treatment failed to improve brain health, measured by brain lesion volume and brain volume changes [3; 4].
In healthy adults, a single dose of EGCG has little influence on cognition. One double-blind randomized controlled trial reported that a single treatment did not affect cognitive performance or mood [5]. A second trial reported increased calmness and reduced stress [6]. EGCG also increased brain waves, which have been associated with relaxation, focused attention, and quiet wakefulness [7]. Long-term rigorously-designed clinical trials in healthy adults are needed to evaluate the effects of EGCG on cognitive function.
Preclinical studies have found a wide range of actions of EGCG, including chelating metals, reducing inflammation, scavenging free radicals, improving mitochondrial function, and preventing death of brain cells [8]. EGCG may also inhibit enzymes that break down the neurotransmitter? acetylcholine [9; 10], which is important for memory retrieval. Other preclinical studies found that EGCG treatment improved function or reduced damage in the brain [11; 12; 13], but these effects have not been confirmed in human trials.
In a randomized placebo-controlled trial of APOE4 carriers with subjective cognitive decline (60-80 years old), a multimodal lifestyle intervention (dietary counseling, physical activity, and cognitive stimulation) combined with EGCG for 12 months did not significantly improve overall cognitive functions compared to multimodal lifestyle intervention combined with placebo [14]. However, participants receiving the multimodal lifestyle intervention with EGCG were 2.6 times more likely to show cognitive improvement than participants receiving multimodal lifestyle intervention and placebo. Larger trials are needed to further investigate the effects of adding EGCG to lifestyle interventions.
For more information on what the APOE4 gene allele means for your health, read our APOE4 information page.
No studies have reported whether EGCG alone is beneficial to patients with dementia. While some benefits have been observed in preclinical studies of Alzheimer’s disease, including improved cognitive function [11; 12] and reduction of pathological markers of Alzheimer’s [12], these effects have yet to be confirmed in people with dementia.
EGCG supplements are considered safe for most people when taken at commonly-used doses (300–400 mg/day) [15; 16], but higher doses (800–1600 mg of EGCG per day) may negatively affect liver function [3; 4; 17; 18]. Most safety data on long-term EGCG intake come from large meta-analyses of tea consumption, which have reported that side effects are mild [19; 20] and can include nausea and upset stomach [16; 21].
Three drugs—warfarin (also known as Coumadin™ and Jantoven™), anisindione (or Miradon™), and dicumarol—are known to interact with green tea that contains EGCG, but the interactions are minor [22]. For more information on green tea, please review our separate report on Green Tea.
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
EGCG is abundant in green tea. Sencha, one of the most common types of green tea, contains 25–250 mg of EGCG in a cup (200 mL) [23; 24; 25; 26]. Levels of EGCG can vary widely depending on how much tea leaves is used and how it is brewed. Black tea contains lower levels of EGCG (~20 mg) as it is converted during the oxidation process to thearubigin, a different type of polyphenol [24]. EGCG and other tea catechins are also available as dietary supplements, often in doses of 200–300 mg per serving, which are comparable to doses deemed safe in clinical trials [15; 16]. Higher doses can pose health risks, for example to liver function [3; 4; 18]. Clinical trials examining the effects of EGCG on cognitive function have used doses ranging from 9 to 300 mg/day [6].
Full scientific report (PDF) on Cognitive Vitality Reports
An analysis of commercially available green tea supplements