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Thursday, 6 February, 2025
HomeEditor's PickGreen tea reduces cognitive decline – Japanese study

Green tea reduces cognitive decline – Japanese study

For centuries, people have extolled the health benefits of green tea, like reducing the risk of cardiovascular disease, maintaining skin health, promoting weight loss, and even lessening the risk of dementia.

Now, recent research from Japan adds to the evidence that it helps fight cognitive decline and thus reduces dementia risk, with the scientists finding that older people who regularly drank green tea had fewer of the brain lesions characteristic of dementia than those who did not drink it.

The study was published in Science of Food.

Steven Allder, MD, a consultant neurologist at Re:Cognition Health, who was not involved in this study, told Medical News Today that while the link between green tea and fewer cerebral lesions “highlights its potential as a preventive strategy against age-related cognitive decline”, the results should be interpreted cautiously, “as confounding variables like lifestyle and dietary habits may contribute to these outcomes”.

Antioxidants

Green tea has one of the highest levels of antioxidants of any tea, as well as polyphenols, which could bring various health benefits, including: helping combat some cancers, including those of the breast, gastrointestinal tract, lung, prostate and liver; encouraging weight loss; anti-inflammatory effects on the skin and cardiovascular system; and cognitive benefits.

The study, led by Kanazawa University Graduate School of Medical Sciences, investigated almost 9 000 adults recruited from the Japan Prospective Studies Collaboration for Ageing and Dementia between 2016 and 2018, to determine whether green tea or coffee had any effect on brain health.

All participants filled in a Food Frequency Questionnaire, with their daily intake of green tea and coffee being classified into four groups: 0-200ml, 201-400ml, 401-600ml, and at least 601ml.

One cup of tea was equivalent to 200ml.

They also underwent magnetic resonance imaging (MRI) scans to assess cerebral white matter lesions, hippocampal volume and total brain volume.

The researchers controlled for sociodemographic factors, such as age, sex and education level, and in a second analysis, adjusted for medical factors, including hypertension, diabetes mellitus, APOE e4 allele (which increases dementia risk), body mass index (BMI), cholesterol levels, smoking and drinking habits, ECG abnormalities, history of stroke, depressive symptoms, cognitive function and regular exercise.

They excluded 1 519 participants who had mild cognitive impairment at baseline. In further analysis, the researchers investigated whether depression or having the APOE e4 allele had any effect on their results.

Fewer lesions

After adjusting for confounding factors, they found a significant association between higher green tea consumption and fewer cerebral white matter lesions.

They did not see any association with coffee consumption. They also found no association with hippocampal or total brain volume.

Allder explained why they might have seen these effects: “This could be due to the neuroprotective properties of catechins like EGCG in green tea, which combat oxidative stress, reduce inflammation and inhibit beta-amyloid aggregation.”

Coffee did not show similar benefits, possibly because green tea’s unique composition, like catechins, might be more effective against white matter lesions than coffee’s compounds, which are mainly chlorogenic acid and caffeine, he added.

The effects of green tea did not, however, extend to participants with the APOE e4 allele, or those with depression.

In these people, the researchers found no association between green tea and fewer brain lesions. They suggest that, as both are strong risk factors for dementia, green tea may not be effective in reducing white matter lesions in these individuals.

Allder agreed. “The absence of benefits in people with depression might be due to the interaction between chronic inflammation and oxidative stress associated with depression, which could counteract the neuroprotective effects of green tea.

“Similarly, the lack of effect in APOE e4 carriers suggests a genetic predisposition that could diminish green tea’s impact, potentially due to APOE e4's strong association with amyloid pathology and vascular contributions to cognitive impairment.”

Any side effects from green tea?

Unlike black tea, green tea is not fermented, so retains polyphenols, such as flavanols, of which catechins are particularly important. Catechins are antioxidants that neutralise free nitrogen and oxygen radicals, with studies showing they reduce the inflammation that may lead to many chronic and age-associated conditions – like some cancers, cardiovascular diseases and neurodegenerative diseases.

The researchers warn that there were limitations to the study: it was cross-sectional so they cannot determine a causal relationship between green tea consumption and reduced white matter lesions.

Also, they could not account for how the tea was brewed, or whether participants were also consuming it in snacks. And, because there were few black tea drinkers in their Japanese cohort, they could not compare the effects of green and black teas.

Allder called for further studies on diverse populations, different ethnic groups and in different regions, to determine whether genetic and lifestyle factors influence the benefits of green tea.

“Research should also focus on targeted subgroups, like people with depression or the APOE e4 allele, to explore the mechanisms that might limit green tea’s effectiveness in these populations.

Study details

Green tea consumption and cerebral white matter lesions in community-dwelling older adults without dementia

Shutaro Shibata, Moeko Noguchi-Shinohara, Ayano Shima et al.

Published in NPJ Science of Food on 7 January 2025

Abstract

This study investigated the association between green tea or coffee consumption with cerebral white matter lesions and hippocampal and total brain volumes among 8766 community-dwelling participants recruited from the Japan Prospective Studies Collaboration for Ageing and Dementia between 2016 and 2018. A Food Frequency Questionnaire was used to assess green tea and coffee consumption, whereas brain magnetic resonance imaging was performed to assess cerebral white matter lesions, hippocampal volume, and total brain volume. Multivariable-adjusted analysis revealed significant correlations between fewer cerebral white matter lesions and higher green tea consumption, whereas no significant differences were found between green tea consumption and hippocampal or total brain volume. Regarding coffee consumption, no significant differences were observed in cerebral white matter lesions or hippocampal or total brain volumes. Hence, higher green tea consumption was associated with fewer cerebral white matter lesions, suggesting that it may be useful in preventing dementia.

 

NPJ Science of Food article – Green tea consumption and cerebral white matter lesions in community-dwelling older adults without dementia (Open access)

 

Medical News Today article – Green tea drinkers have fewer brain lesions linked to dementia (Open access)

 

See more from MedicalBrief archives:

 

Green tea extract promotes gut health, lowers blood sugar – Ohio study

 

Benefits of green tea revealed in new pancreatic cancer study

 

Additive effects of green tea and coffee on mortality risk in type 2 diabetes patients

 

 

 

 

 

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