Green Tea Could be the Cognitive Key

Animal studies demonstrate several ways GT might be acting to prevent cognitive decline. Rezai-Zadeh et al published a study in 2008 examining how oral EGCG supplementation affected the development of brain tissue pathology in mice genetically engineered to develop a mouse equivalent version of Alzheimer’s disease (AD).² Investigators treated these mice for six months starting at 8 months of age and then examined their brain tissue using multiple modalities.

Beta-amyloid plaques^a and the concentration of beta amyloid in key areas of the brain typically affected by AD, including the hippocampus (the brain’s memory center) and the surrounding entorhinal cortex were significantly decreased. Water soluble (dissolvable) phosphorylated tau^b levels were also inhibited by EGCG, which was administered either orally or via injection into the abdominal cavity. Finally, investigators evaluated the working memory of EGCG- treated mice compared to controls using a water maze. Treatment with EGCG improved working memory performance.

EGCG’s potent antioxidant activity is also likely playing a direct neuroprotective role. Cerebrovascular disease (disease of the blood vessels supplying the brain) is a common cause of cognitive impairment and dementia, termed vascular cognitive impairment (VCI) and vascular dementia (VD), respectively. AD pathology seldom occurs in isolation, and VCI and VD likely contributes to and promotes mild cognitive impairment (MCI) and AD. Xu et al created a rat model of chronically compromised cerebral blood flow and investigated if the behavioral and biochemical damage that ensued could be ameliorated by oral administration of EGCG.³

Four to eight weeks after their cerebrovascular circulation was damaged, rats were given differing doses of GT polyphenols. Investigators then evaluated spatial learning and memory with the Morris water maze. Rats given a dosage of 400 mg/kg of GT polyphenols performed better on the spatial memory task compared to control mice given salt water. Oxidative damage was found to be decreased and antioxidant capacity was enhanced.

Unhealthy diets stimulate brain dysfunction with aging fueled by insulin resistance and poor glucose utilization by brain cells (neurons). Onishi et al published a study in 2019 using a mouse model of cognitive dysfunction generated by a high-fat diet.⁴ For four months, mice genetically engineered to express faster senescence (aging) were administered a control diet, a high-fat diet, or a high-fat diet combined with 0.5% green tea extracts (GTEs). The mice who received the high-fat diet demonstrated impaired memory retention and high levels of beta amyloid in the cerebral cortex. These effects were dampened by concurrent intake of GTEs. These diets also increased the amount of lipid oxidative damage and decreased levels of brain-derived neurotrophic factor (BDNF)^c in the hippocampus. GTEs protected against these developments.

Numerous epidemiological studies on humans have suggested GT protects against cognitive impairment and dementia. In 2006, Kuriyama et al examined 1003 Japanese participants age 70 or older regarding the frequency of their GT intake.⁵ Their cognitive function was then assessed using the mini mental state exam (MMSE), a short, standardized cognitive screening test. Results showed that the likelihood of having a score below 26, which would suggest cognitive impairment, decreased with increasing frequency of GT consumption. The greatest protective benefit was seen with drinking two or more cups of GT daily.

Another epidemiological study by Tomata et al evaluated a cohort of 13,645 Japanese subjects aged 65 or older.⁶ Investigators assessed the risk of development of dementia over the next 5.7 years, which occurred in 8.7% of participants. The incidence of dementia was significantly decreased in those subjects who drank 5 or more cups of GT daily compared to those who had less than one daily cup. Protection against cognitive decline was seen even in those individuals without any subjective cognitive complaints at the start of the study.

In 2011, Park et al reported the cognitive benefit of administering a combination supplement containing GTE and L-theanine to patients with MCI.⁷ They enrolled 91 participants in a 16-week study.

Forty-five participants were in the treatment group and received a daily total of 720 mg of GTE and 120 mg of L-theanine. Neuropsychological tests were then used to evaluate memory and attention and showed enhanced performance on the memory test at 8 weeks. LGNC-07 significantly improved memory test scores at 16 weeks and color-word test scores at 8 weeks in subjects with lower MMSE (21-23).

Electroencephalogram (EEG) analysis also showed brain wave changes correlated with better attention and memory in the group that received GTE and L-theanine.

In general, green tea is well tolerated. The preponderance of the evidence does suggest a protective effect against cognitive decline. Most of its side effects come from the presence of caffeine, which can lead to nervousness, irregular heart rhythm, and insomnia. It also decreases absorption of iron, which would be concerning to individuals with iron-deficiency anemia.⁸ Because of its vitamin K content, GT can also interfere with the prescription blood thinner, warfarin, which acts by inhibiting vitamin K.

Sprouts has a Jarrow brand GTE, which usually sells for $14 for a bottle of 100 (500-mg strength) capsules. Each capsule consists of 50% polyphenols and 30% catechins, including EGCG, along with 40 mg of caffeine. Many other brands are also readily available. A bottle of 90 (150-mg) capsules of Doctor’s Best brand L-theanine can be purchased online for $13. Green tea is perhaps best enjoyed as a hot beverage and decaffeinated options are available.

a. Beta amyloid plaques are one of the two key abnormal protein deposits used to identify the pathology of AD. The plaques are found outside of neurons, the defining cells of the nervous system.

b. Water-soluble phosphorylated tau clumps together inside neurons to form tau tangles, the other abnormal protein deposit used to identify the pathology of AD.

c. BDNF, often referred to as “Miracle Grow” for the brain, is an important signaling protein that plays a central role in the differentiation of neurons (the maturation of neurons from precursor cells), neuronal health and maintenance, as well as the growth of new neurons, known as neurogenesis.

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2. Rezai-Zadeh K, et al. Green tea epigallocatechin-3-gallate (EGCG) reduces β-amyloid mediated cognitive impairment and modulates tau pathology in Alzheimer transgenic mice. Brain Res. 2008;1214:177-187. doi: 10.1016/j.brainres.2008.02.107.

3. Xu Y, et al. Green tea polyphenols inhibit cognitive impairment induced by chronic cerebral hypoperfusion via modulating oxidative stress. J Nutritional Biochem. 2010:(21)8:741-748. doi: 10.1016/j.jnutbio.2009.05.002.

4. Onishi S, et al. Green tea extracts attenuate brain dysfunction in high-fat-diet-fed SAMP8 mice. Nutrients. 2019;11(4):821. doi: 10.3390/nu11040821.

5. Kuriyama S, et al. Green tea consumption and cognitive function: a cross-sectional study from the Tsurugaya Project. Am J Clin Nutr. 2006;83(2):355-361. doi: 10.1093/ajcn/83.2.355.

6. Tomata Y, et al. Green tea consumption and the risk of incident dementia in elderly Japanese: the Ohsaki Cohort 2006 Study. Am J Geriatr Psychiatry. 2016;24(10):881-889. doi: 10.1016/j.jagp.2016.07.009.

7. Park S-K, et al. A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study. J Med Food. 2011;14(4):334-343. doi: 10.1089/jmf.2009.1374.

8. Nawab A, Farooq N. Review on green tea constituents and its negative effects. Pharm Innov J. 2015;4(1):21-24.