Assessing Green Tea’s Neuroprotective Potential

Green tea, which comes from the plant Camellia sinensis, has garnered much attention in recent years for its purported health benefits, with marketers touting the antioxidant, cardioprotective, and anticarcinogenic properties associated with it. Some also assert that green tea, and matcha in particular, has a neuroprotective effect, suggesting a potential role for green tea consumption in the prevention of neurodegenerative diseases, such as Alzheimer’s dementia. Despite their widespread impact, most of these diseases remain incurable, and treatments are focused on alleviating symptoms and slowing disease progression. Efforts to prevent or reduce the risk of neurocognitive decline have thus gained traction in recent years, and perhaps unsurprisingly, green tea is among those compounds being studied.

The leaves of the plant Camellia sinensis are used to make green, black, and oolong teas (Afzal et al. 2022). Each type is differentiated by the degree to which the leaves are fermented. Green tea is made from the unfermented leaves and generally contains a greater concentration of polyphenolic compounds than black or oolong teas, which are fully and semi-fermented, respectively (Afzal et al. 2022). Catechins, a group of flavonoids, make up about three-quarters of the polyphenols in green tea and are responsible for most of its antioxidant properties (Afzal et al. 2022).

Matcha (powdered Japanese green tea) is unique in that it allows people to consume the tea leaves in their entirety, rather than just the extract (Sokary et al. 2022). The polyphenolic and caffeine content of matcha is thus higher than that of loose-leaf green tea (Sokary et al. 2022). Moreover, its versatility makes it attractive to product developers and consumers alike. Matcha is frequently added to various drinks, snack bars, and desserts, lending its subtle earthy flavor to these items.

Catechins have several plausible mechanisms of action by which they can exert neuroprotective effects. As antioxidants, they may reduce oxidative stress and inflammatory cytokines in the brain, thereby decreasing neuronal death (Afzal et al. 2022). In vitro studies have demonstrated the ability for catechins to chelate copper and iron ions, both of which have been found in increased concentrations in people with Alzheimer’s dementia (Afzal et al. 2022). They may also inhibit beta-amyloid plaque formation and acetylcholinesterase activity, which are implicated in multiple neurological disorders (Afzal et al. 2022).

Real-world studies of green tea have yielded more equivocal results. One study published in 2016 demonstrated that older Japanese adults who drank five or more cups of green tea per day had a significantly lower risk of dementia than those who drank less than one cup of green tea per day (Tomata et al. 2016). On the other hand, a 2021 prospective cohort study of older Japanese adults found no significant correlation between green tea consumption and risk of dementia when results were adjusted for age. Interestingly, though, coffee consumption of three or more cups per day was associated with a 50% decreased risk of dementia (Matsushita et al. 2021). That said, both studies had limitations. The type of green tea—matcha versus loose-leaf—was not specified in either study. The 2016 study only collected dietary data at baseline, and thus could not account for changes in green tea consumption or diet that occurred during follow-up (Tomata et al. 2016). The 2021 study did not adjust any of the results for other dietary factors (Matsushita et al. 2021).

As for matcha green tea, a 12-week randomized controlled trial published in 2020 investigated the impact of supplemental matcha compared to placebo on cognitive function as measured on clinical questionnaires (Sakurai et al. 2020). Participants in the experimental group received a total of 3 g of matcha per day, served in the form of drinks. When looking at the entire cohort, supplementation with matcha green tea powder had no effect on cognition compared to placebo, although subgroup analyses demonstrated a significant improvement for females but not males (Sakurai et al. 2020). However, the sample size was small, with only 54 participants overall, mostly female. Perhaps more importantly, it is unclear if the statistically significant improvements seen correlated to improvements in quality of life (Sakurai et al. 2020).

In summary, there is some evidence to suggest that green tea may reduce the risk of dementia, as well as a theoretical mechanism by which it may reduce the risk of other neurological disorders. Because of its concentrated nature and widespread applicability in the food market, matcha in particular appears to be a promising subject for future research.ft