Tea/Tea component

Potential Mechanisms of action

Source

γ-Aminobutyric acid

GABA may alleviate stress induced by mental tasks -EEG activities including alpha band and beta band brain waves decreased.

Yoto, et al. [21]

Black tea aroma

Inhalation of black tea aroma (Darjeeling and Assam) reduced salivary chromogranin-A levels - a marker of stress.

Yoto, et al. [46]

Epigallocatechingallate/Green TeaExtracts/Catechins

EGCG appears to induce a relaxed and more attentive state after consumption.

Scholey, et al. [26]

EGCG undergoes microbial degradation in the small and large intestine resulting in the formation of microbial ring-fission metabolites which could reach the brain parenchyma through the blood-brain barrier and induce neuritogenesis.

Pervin, et al. [25]

Green tea extract activated brain activity in the DLPFC - a key area that mediates working memory processing in the human brain.

Borgwardt, et al. [27]

Green tea improves psychopathological symptoms (e.g. reduced anxiety), cognition (e.g. benefits in attention/memory) and brain function (e.g. activation of working memory).

Mancini, et al. [10]

These may prevent age-related neurodegeneration through improved antioxidant defence mechanisms, modulation of neural growth factors, attenuation of neuroinflammatory pathway, and regulation of apoptosis.

Farzaei, et al. [23]; Pervin, et al. [22]

L-theanine& Caffeine

L-theanine significantly increased activity in the alpha frequency band indicating that it relaxes the mind without inducing drowsiness.

Nobre, et al. [31]

L-theanine at particular dosages (200-400 mg/d) has been found to increase sensorimotor gating in humans and assist in the reduction of anxiety and stress amongst those exposed to stressful conditions.

Ota, et al. [38]; Williams, et al. [30]

Caffeine may improve performance on demanding long-duration cognitive tasks and self-reported alertness, arousal, and vigor at low doses of 40 mg. L-theanine alone improved self-reported relaxation, tension, and calmness starting at 200 mg.

Dietz & Dekker [29]

L-theanine and caffeine may be reduce deviation of attention to distractors (i.e. mind wandering) subsequently enhancing attention.

Kahathuduwa, et al. [28]

Polyphenols

Polyphenols including EGCG can inhibit the activation of caspase-3 and modulate mitogen-activated protein kinases known to play an important role in neuronal apoptosis.

Bastianetto, et al. [24]

Other constituents

Bioactives in tea have been found to have anti-amyloid effects in epidemiological research.

Polito, et al. [52]

Teasaponin along with L-theanine, EGCG, catechins and their metabolites appear to up-regulate the ERK/CREB/BDNF signalling pathway which could collectively reduce depression risk.

Rothenberg, et al. [44]