Recent research indicates that consuming three or more cups of green tea daily may protect brain health. Avoiding tea bags is advised, as previous studies show that commercial polymer-based tea bags can release millions of nanoplastics and microplastics when steeped.
The study, led by Shutaro Shibata from Kanazawa University in Japan, found a significant relationship between higher green tea consumption and fewer white matter lesions in the brain, which often indicate small vessel disease.
Published in npj Science of Food on January 7, 2025, the findings suggest that drinking three cups of green tea or more daily can help protect brain health, while coffee consumption did not show significant effects.
This research was part of the Japan Prospective Studies Collaboration for Aging and Dementia, a large observational study involving eight research centers in Japan.
Both green tea and coffee are known for their neuroprotective compounds and are among the most consumed beverages globally after water. Previous studies have linked tea and coffee intake to cognitive benefits, but few have directly examined their relationship with structural brain changes in older adults.
White matter lesions, often indicating small vessel disease, have been associated with cognitive decline, vascular dementia, and Alzheimer’s disease. The current study aimed to evaluate the impact of green tea and coffee consumption on white matter lesion volume, hippocampal volume, and total brain volume using MRI data.
Data collection occurred between 2016 and 2018, involving dietary assessments, MRI scans, and cognitive evaluations of 8,766 participants aged 65 and older. A Food Frequency Questionnaire was used to measure daily green tea and coffee intake, categorized into four levels: 0-200 ml, 201-400 ml, 401-600 ml, and ≥ 601 ml.
MRI scans provided data on white matter lesion volume, hippocampal volume, and total brain volume. Advanced statistical models adjusted for confounding factors such as demographics, health conditions, lifestyle habits, and genetic risk factors for Alzheimer’s disease.
The analysis excluded participants with mild cognitive impairment, dementia, or incomplete data, narrowing the final group to 8,766 individuals.
After adjusting for confounding factors, higher green tea consumption was significantly associated with lower white matter lesion volume. Participants consuming 600 ml (approximately three cups) of green tea daily had 3% lower white matter lesion volume than those consuming 200 ml or less. Those consuming 1,500 ml daily had 6% lower white matter lesion volume compared to the reference group.
The study also found no significant relationship between green tea intake and total brain volume or hippocampal volume. Coffee consumption did not significantly affect white matter lesion volume, hippocampal volume, or total brain volume.
These findings indicate that the antioxidant and anti-inflammatory properties of green tea catechins, such as epigallocatechin gallate, may reduce vascular damage and enhance brain health, although specific components have not been experimentally validated as causative.
Concerns arise that the benefits of green tea may be compromised when brewed using tea bags, as previous research indicated that commercial polymer-based tea bags could release millions of nanoplastics and microplastics during brewing.
Research published in Chemosphere in December 2024 demonstrated for the first time how microplastics and nanoplastics from tea bags could be absorbed by intestinal cells and thus enter the bloodstream, spreading throughout the body.
Microplastics are defined as fragments ranging from 5 millimeters to 1 micrometer, while nanoplastics are smaller than 1 micrometer. In comparison, human hair measures about 70 micrometers.
The Mutagenesis Group at Universitat Autònoma de Barcelona characterized micro and nano plastics from various commercially available tea bags. Researchers observed that brewing tea released significant amounts of nano-sized particles and nanofiber structures, representing a major source of plastic exposure.
The tea bags used in this study were made from nylon-6, polypropylene, and cellulose. The research indicated that brewing tea released approximately 1.2 billion polypropylene particles per milliliter, with an average size of 136.7 nanometers; cellulose released about 135 million particles per milliliter with an average size of 244 nanometers; while nylon-6 released 8.18 million particles per milliliter with an average size of 138.4 nanometers.
The results underscore the important role of intestinal mucus in absorbing these pollutant particles and highlight the need for further research on the chronic exposure effects on human health.