Habitual tea drinking modulates brain efficiency: evidence from brain connectivity evaluation

Abstract

The majority of tea studies have relied on neuropsychological measures, and much fewer on neuroimaging measures, especially for interregional connections. To date, there has been no exploration of the effect of tea on system-level brain networks. We recruited healthy older participants to two groups according to their history of tea drinking frequency and investigated both functional and structural networks to reveal the role of tea drinking on brain organization. The results showed that tea drinking gave rise to the more efficient structural organization, but had no significant beneficial effect on the global functional organization. The suppression of hemispheric asymmetry in the structural connectivity network was observed as a result of tea drinking. We did not observe any significant effects of tea drinking on the hemispheric asymmetry of the functional connectivity network. In addition, functional connectivity strength within the default mode network (DMN) was greater for the tea-drinking group, and coexistence of increasing and decreasing connective strengths was observed in the structural connectivity of the DMN. Our study offers the first evidence of the positive contribution of tea drinking to brain structure and suggests a protective effect on age-related decline in brain organisation.

Keywords: DTI; brain efficiency; default mode network; fMRI; hemispheric asymmetry; tea drinking.

Figure 1

Comparisons of neuropsychological and cognitive measures between the tea drinking group (T) and non-tea drinking group (NT). A non-parametric permutation test was used to evaluate the significance level in group differences by permuting 10,000 times (* corrected p<0.05). Abbreviations: RAVLT_ir, Rey Auditory Verbal Learning Test with immediate recall; RAVLT_dr, Rey Auditory Verbal Learning Test with delayed recall; DigitSpan_fwd, forward Digit Span; DigitSpan_bwd, backward Digit Span; SDMT_written, Symbol Digit Modalities Test by written response; SDMT_oral, Symbol Digit Modalities Test by oral response; BostonNaming, Boston Naming Test; BlockDesign, Block Design tests from the Wechsler Adults Intelligence Scale (WAIS-III); CTT1, Color Trials Test 1; CTT2, Color Trials Test 2; MMSE, Mini-Mental State Examination, MoCA, Montreal Cognitive Assessment.

Figure 2

Comparisons of global graph theoretical metrics between tea drinking (T) and non-tea drinking groups (NT). (A) Metrics computed on the functional connectivity network. (B) Metrics calculated on the structural connectivity network. Asterisks represent significance level obtained by permutation test (* corrected p< 0.05).

Figure 3

Brain regions exhibiting significant differences in structural nodal efficiency between the tea drinking group and the non-tea drinking group at the significance level of 0.01 (uncorrected) statistical evaluated by a permutation test.

Figure 4

Comparisons of hemispheric asymmetries of global graph theoretical metrics between the tea-drinking group (denoted by T) and the non-tea drinking group (denoted by NT). A positive value in the hemispheric asymmetry indicates the leftward hemispheric asymmetry while a negative value indicates the rightward hemispheric asymmetry. Asterisks represent significance level obtained by permutation test (* corrected p< 0.05). (A) Hemispheric asymmetries of global graph theoretical metrics for functional connectivity network. (B) Hemispheric asymmetries of global graph theoretical metrics for structural connectivity network.

Figure 5

Connections with significantly different strengths between the tea drinking group and the non-tea drinking group within the default mode network. Significance was established by setting uncorrected p<0.05 with the permutation test. (A) Differences of connective strengths between the groups (tea drinking group minus non-tea drinking group) for significant connections in the functional network. (B) Differences of connective strengths between the groups for significant connections in the structural network.