A recent study showed that people who drink tea regularly have brains which function better and also show a greater degree of organization. This could strengthen the case for drinking tea to help prevent dementia. The study is important because, unlike most others which look only at tests of mental ability, it also examined structural brain changes with tea drinking.
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Prior research shows that drinking tea is good for health, improving the mood and benefiting heart health. An older larger study by the same researcher on a thousand participants showed a 50% less decline in cognitive health with daily consumption of tea. However, in the present study, the team took it forward to explore how tea affected the brain circuits directly.
Tea is a time-honored drink and those who enjoy their cuppa share an ancient lineage dating back to 2700 BC, when the Chinese Shen Nong dynasty are recorded to have brewed their own tea. Unlike most other beverages, drinking tea is unequivocally linked to better heart health, better memory and thinking, less stress, a lower cancer risk and an overall reduced risk of premature death. This is attributed to plant compounds like catechin and L-theanine which are associated with positive effects on memory, stress, and other psychological measures.
How was the study done?
The study included 36 people aged at least 60 years who were asked about their health, lifestyle and diet, as well as mental well-being. They were then tested for nervous and psychological function, and brain MRI scans were performed. After analysis, the study found that consumption of green tea, oolong and black tea four times or more a week for 25 years positively affected the organization of brain circuits, making for efficient data processing or better cognitive functioning.
And the outcomes…
The results showed noticeably better structural connectivity between related brain regions, though there were no significant differences in the functional connections. Six regions in the frontal lobe were significantly better connected in terms of functional connectivity in tea drinkers compared to non-tea drinkers. The two hemispheres showed more equal functional connections in the tea drinkers compared to the non-tea drinkers, though not to a significant level. However, the structural difference between the brain circuits between the hemispheres did show significant variation. Drinking tea was associated with a lower level of asymmetry favoring the left side of the brain.
The researchers tested the structural and functional connectivity within what is called the default mode network of the brain, which is primarily involved in dementia. This showed better functional connectivity in 11 circuits in tea drinkers. However, there was no uniform effect on the structural connectivity which showed both increases and decreases in tea drinkers, compared to the other group.
Six regions (mostly in the front part of the brain) that are responsible for nodal connections also showed better structural efficiency in tea drinkers. This is reasonable, given that this region of the brain is closely related to aging-related decreases in brain organization.
What does tea do?
The findings from the current study not only confirmed earlier research but showed one way this could be explained. Tea drinking seems to help retain intact neural connections between related brain regions, making the aging brain more organized.
Researcher Lei Feng says, “When a road system is better organised, the movement of vehicles and passengers is more efficient and uses less resources. Similarly, when the connections between brain regions are more structured, information processing can be performed more efficiently.”
Why weren’t there any significant differences in functional connectivity between tea drinkers and non-tea drinkers? The researchers offer some explanations. First, the brain is well known to compensate for any structural change to a very large extent, and this could well hide any loss of functional connectivity with age in non-tea drinkers. Secondly, such losses could be too subtle to be picked up by measures used in the current study. However, eventually neurocognitive losses do override the compensation mechanisms. The current study seems to show this in action, since non-tea drinkers showed lower visuospatial function, but no significant differences were seen in the other neuropsychological tests.
The finding that tea drinking reduced the functional asymmetry of the hemispheres should be viewed against the knowledge that asymmetry develops in a U-shape, being first leftward in childhood, rightward in middle age, and then again moving to the left in old age. In that case, the current study suggests a slowing of the leftward shift that is expected with old age, enabling the brain to retain more of a middle-aged profile. This could also explain the better visuospatial processing results in tea drinkers, since this function is performed largely in the right hemisphere.
Tea intake also prevents the decline of cognitive functions related to poorer functional connections in the default mode network. This showed increases of connectivity in some areas while others showed a decline, in the groups of tea drinkers. This could be because new pathways could develop to replace those lost to age-related disruption of existing routes.
Feng sums up: “Our study suggests tea drinking is effective in preventing or ameliorating cognitive decline and that tea drinking might be a simple lifestyle choice that benefits brain health.”
The scientists now want to understand what compounds in tea affect the brain circuits, and how. This could help explain how memory is related to brain networks, and how this can be manipulated to prevent memory loss with aging.
The study was published in the journal Aging.
Habitual tea drinking modulates brain efficiency: evidence from brain connectivity evaluation. Junhua Li, Rafael Romero-Garcia, John Suckling, & Lei Feng. Aging. https://doi.org/10.18632/aging.102023. https://www.aging-us.com/article/102023/text