Green tea extract may benefit cognitive functioning, particularly working memory, according to a new study. Green tea is made from the dried leaves of Camellia sinensis , an evergreen shrub.

Green tea, black tea, and oolong tea all come from the same plant. Green tea is made by lightly steaming the freshly cut leaf. Green tea is primarily made and consumed in China, Japan, and countries in North Africa and the Middle East. Unlike black and oolong tea leaves, green tea leaves do not undergo a fermenting process.

As a result, green tea has higher levels of antioxidant compounds. In a recent study, researchers randomly assigned 12 healthy people to receive a milk drink containing The effects of green tea on working memory and the connectivity between the frontal lobe, which plays an important part in retaining memories, and the parietal lobe, which plays an important role in processing the senses such as touch and taste, were evaluated.

The researchers found that green tea extract increased working memory and the connectivity between the frontal and parietal lobes of the brain. This increase in connectivity was related to an improvement in the performance of tasks. The authors concluded that the benefits of green tea extract on mental function and memory may play an important role in potential treatment options for people with mental disorders or memory loss.

Further research is warranted. The endogenous antioxidant defense mechanism Burckhardt et al. In terms of oxidative stress, superoxide dismutase SOD acts as one of the key enzymatic antioxidant defenses against superoxide radicals.

Malondialdehyde MDA is the principal end-product in the lipid peroxidation process and is cytotoxic Xu et al. Glutathione peroxidase GPx is an important peroxide decomposing enzyme widely present in the body Biasibetti et al.

Glutathione reductase GR functions in catalyzing an oxidized form of glutathione into a reduced form. They play an essential role in preventing the oxidative decomposition of hemoglobin, maintaining the activity of sulfhydryl proteins, ensuring the reducibility of sulfhydryl proteins, and cell integrity Rubio-Perez et al.

Therefore, our study selected the four biomarkers above for testing. Two main hypotheses were suggested for the primary AD pathogenesis Torres et al. One is the amyloid cascade hypothesis.

Amyloid-β Aβ deposition is widely accepted as central to AD pathology, of which Aβ 40 and Aβ 42 are the most common subtypes in the human body. The other hypothesis refers to abnormal phosphorylation of tau. Tau is a microtubule-associated protein, while hyperphosphorylation of tau leads to the formation of neurofibrillary tangles.

In recent years, phosphorylated tau pTau is considered to be a potential AD blood marker, which may predict the longitudinal progress of AD Janelidze et al. Accordingly, the three indicators above, namely Aβ 40 , Aβ 42 , and pTau , were selected for detection in terms of anti-AD pathology.

A total of subjects were screened at the Department of Neurology and Physical Examination Center in Zhongnan Hospital of Wuhan University from October to December The inclusion criteria included subjects: 1 aged 50—70 years old, 2 who had received at least primary education, and 3 who could provide voluntary written informed consent.

Subjects were excluded who: 1 had a recent record of severe cerebrovascular disease found on MRI or CT, 2 have been diagnosed with dementia according to DSM-V American-Psychiatric-Association, , 3 showed obvious auditory or visual handicaps, or 4 suffered from other severe diseases that significantly affect cognitive function including the depression or anxiety status, thyroid disease, infection, tumor, or systemic disease.

In this study, participants were interviewed by one specific staff to acquire data regarding demographic information, medical history, and green tea consumption.

Thereafter they received an assessment of cognitive function at the memory outpatient clinic. Finally, 5 ml of fasting venous blood sample was collected from each subject. After excluding subjects who did not complete the full set of cognitive assessments 68 subjects or lacked blood samples subjects , subjects were admitted to the final analyses, including males and females, with an average age of gov ID: NCT See participant flowchart Figure 1.

Tea consumption information was obtained by direct interviewing with the following four questions: Q1 the type of tea most commonly consumed green tea, black tea, oolong tea, or others , Q2 the consumption frequency days per week , Q3 the daily volume of tea cups per day , and Q4 the duration of tea consumption habit years.

A cup of standard green tea has a volume of ml. First, we divided the subjects into two groups for preliminary analysis.

Body mass index BMI was calculated as weight kg divided by the square of height m. Participants also reported if they had a history of hypertension, hypercholesterolemia, diabetes, or atrial fibrillation.

All the information above was determined by the same researcher. Fasting blood glucose, total cholesterol, triglyceride, and homocysteine levels were measured by the laboratory department of Zhongnan hospital. These characteristics were identified because they are risk factors for cognitive function or have effects on cognitive function and can be potential confounders.

Every subject underwent a battery of neuropsychological tests to assess cognitive functions covering the five main cognitive domains of memory, language, attention, executive function, and visual space Table 1 for details , all completed by the same experienced memory clinicians.

The Montreal Cognitive Assessment MoCA is a screening test assessing the global cognitive function that covers memory, visuospatial ability, executive function, attention, concentration, working memory, and orientation.

At present, there are still different reports on the normal value of MoCA. The Hopkins Verbal Learning Test-Revised HVLT-R consists of immediate recall after three consecutive learning, delayed recall, and delayed recognition after min intervals used to measure verbal memory in all participants.

The Verbal Fluency Test requires the subject to list as many examples as possible in 1 min in a certain category. The three categories in our study used to evaluate language function are animals, fruits, and vegetables. Trail Making Test TMT is divided into two parts, A and B.

Part A requires the subjects to connect the circled numbers from 1 to 25 in sequence. In Part B, the circles include both numbers one and Chinese characters One and the subject should draw a line to connect alternative numbers and characters in ascending order i.

TMT-A and B are aimed to assess attention and executive function. The Symbol Digit Modalities Test contains a series of numbers between one and nine. Subjects are required to fill in the corresponding symbol based on a digit-symbol key provided within 90 s to measure their attention and processing speed.

Victoria Stroop Test VST consists of three trials: a word, a color, and a word-color interference trial. Subjects need to read the colors in each card as quickly as possible. Interference scores were calculated as the time difference for completion of the interference measures minus the non-interference tasks, used to assess executive function.

Clock Drawing Test requires subjects to draw a rounded clock on white article, fill in all the numbers, and indicate a certain time to measure visual space ability.

Hamilton Anxiety Rating Scale and Hamilton Depression Rating Scale were used to exclude subjects with moderate to severe anxiety or depression. Thus, subjects who have developed dementia are excluded. AD markers were all measured with enzyme-linked immunosorbent assay ELISA.

Serum Aβ 40 and Aβ 42 levels were detected by human Aβ 40 and Aβ 42 ELISA kits Reddot, British Columbia, Canada , and serum pTau levels were determined by human phosphorylated Tau Protein ELISA kit Jianglai Biological, Shanghai, China.

Oxidative stress markers were all measured with biochemical kits Nanjing Jiancheng, Nanjing, China. The whole detection was used in a blinded manner with respect to subject information.

Gender, education level, smoking history, alcohol consumption, history of hypertension, hypercholesterolemia, diabetes, and atrial fibrillation were considered to be categorical variables.

These were shown as the number of cases percentage and analyzed by the chi-square test. The remaining items were continuous variables and presented as mean ± standard deviation Mean ± SD.

Two independent-sample t-tests werea used for comparisons between two groups of normal distribution and one-way analysis of variance was used among multiple groups.

Finally, we adopted logistic regression analysis to evaluate the correlation between green tea consumption and MCI, following adjustments for individual characteristics.

Statistical analyses were conducted using SPSS The characteristics of the participants are shown in Table 2 , Figure 2A with cases Differences were observed in gender There were more males, more smokers, and lower physical activity scores in the tea-consuming group, which is consistent with the social phenomenon that middle-aged and elderly men prefer tea consumption.

And the trend of smoking may be related to gender. Figure 2. A First, the subjects were divided into two groups for preliminary analysis, including cases There were 42 cases Table 2. Demographic and clinical characteristics of tea-consuming and non-consuming group.

In subgroup analysis, there were cases Compared with the non-consumption group, the medium and high groups had more males and smokers, but no more for physical activity scores. There were significant differences for MoCA The MoCA, HVLT immediate recall, delayed recall, and delayed recognition scores were higher while the TMT-B time and VST interference time were shorter in the tea-consuming group, as shown in Table 4 ; Figure 3.

It is suggested that green tea consumption has a protective effect on cognitive function in a way, which is mainly reflected in the memory and executive function domain. Figure 3. The difference for MoCA score between non-consuming group and tea-consuming group.

The MoCA score was higher in the tea-consuming group significantly. MoCA, Montreal Cognitive Assessment scale. Table 4. The cognition differences between the non-consuming group and tea-consuming group.

The results of subgroup analysis were similar to the above difference that was mainly reflected in memory and executive function. Compared with the non-consumption group, the low group generally had no significant difference.

The MoCA scores Probably, higher tea consumption frequency and volume have a stronger protective effect on cognitive function. Figure 4. The results of subgroup analysis for MoCA scores.

Compared with the non-consuming group, the MoCA score gradually increased in the low, medium, and high group, of which there was a significant difference only in the medium and high group, but not in the low group.

In terms of anti-oxidative stress, there were significant differences for serum SOD The tea-consuming group had lower serum MDA levels and higher serum SOD and GPx levels, as presented in Table 6 , Figure 5.

Figure 5. The differences in serum AD markers between the non-consuming group and the tea-consuming group. There were significant differences in serum pTau A , Aβ42 C , and total Aβ D levels between the two groups but no difference in serum Aβ40 B levels.

The serum pTau, Aβ42, and total Aβ levels were lower in the tea-consuming group. Aβ, Amyloid-β; pTau, phosphorylated tau Table 6. The biomarker differences between non-consuming group and tea-consuming group. In terms of anti-AD pathology, there were significant differences for serum pTau 3.

The serum pTau , Aβ 42 , and total Aβ levels in the tea-consuming group were lower, as presented in Table 6 and Figure 6. It can be seen that green tea consumption may protect cognitive function by reducing AD pathology and improving anti-oxidative stress capacity.

Figure 6. The differences in serum oxidative stress markers between the non-consuming group and tea-consuming group. There were significant differences in serum SOD A , MDA B , and GPx D levels between the two groups, but no difference in serum GR C levels.

The tea-consuming group had lower serum MDA levels and higher serum SOD and GPx levels. SOD, superoxide dismutase; MDA, Malondialdehyde; GPx, Glutathione peroxidase; GR, Glutathione reductase.

The trend of blood marker levels in subgroup analysis was similar to the above but slightly different.

However, in the pairwise comparison for serum GR with the non-consumption group, the high group showed a significant difference The difference in the pairwise comparison was mainly reflected in the medium and high groups, where the serum MDA levels were lower while the SOD, GPx, and GR levels were higher, but no difference in the low group generally.

The difference in the pairwise comparison was also reflected in the medium and high group, where the serum pTau , Aβ 42 , and total Aβ levels were lower. The results were displayed in Table 7 for details.

Thus, high consumption of green tea is more likely to affect AD pathology and anti-oxidative stress capacity. Statistically, significant inverse associations were observed between green tea consumption and mild cognitive impairment in logistic regression analysis, as shown in Table 8 , Figure 7.

With the non-consumption group as reference, the crude odds ratios of MCI for different groups were respectively 1. We included a variety of potential confounders in our multivariate logistic models. However, the results did not change substantially even after adjustment for these variables.

Figure 7. The logistic regression analysis between green tea consuming and cognitive impairment. Statistically, significant inverse associations were observed between green tea consuming and mild cognitive impairment.

Model 1: Crude model. Model 2: Adjusted for age, gender, education, smoking history, alcohol consuming, BMI, and physical activity scores. OR, odds ratio; CI, confidence interval. Table 8. This study found that higher levels of green tea consumption may exert favorable effects on cognitive function and serum biomarkers of AD and oxidative stress in middle-aged and elderly adults.

As for the assessment of cognitive function, we used a battery of neuropsychological tests containing 11 scales and covering five prime cognitive domains. The results demonstrated that the MoCA scores of the tea-consuming group were significantly higher than that of the non-consumption group and were better as the frequency and volume of tea increased.

In logistic regression analysis, there was a significant negative correlation between green tea consumption and MCI. The higher the levels of tea consumption, the lower the risk of cognitive impairment, which suggests that the protective effect of green tea on cognition may be related to frequency and volume.

Furthermore, green tea consumption mainly affected memory and executive function, which was also consistent with the neuropsychological evaluation of vascular cognitive impairment. The most common impaired cognitive domains in vascular cognitive impairment patients were processing speed and executive function Van der Flier et al.

It follows that green tea is likely to be an intervenable vascular protective factor by acting on cerebral blood vessels and its risk factors to achieve the effect of improving cognition.

There have been many reports in the past on the vascular protective effects of green tea. Antioxidants, such as goji berries, green tea, thymus, and so on, may prevent cellular damage by reducing reactive oxygen species ROS overproduction or interfering in reactions that involve ROS. Increased production of ROS favors vascular dysfunction, inducing altered vascular permeability and inflammation, accompanied by the loss of vascular modulatory function, the imbalance between vasorelaxation and vasoconstriction, and the aberrant expression of inflammatory adhesion molecules Bielli et al.

The mechanism underlying the association between green tea consumption and cognitive function may be concerned with endogenous antioxidant defense and anti-AD pathology. As mentioned above, previous evidence has indicated that, on the one hand, the intervention of green tea in animal models of cognitive impairment could change the levels of oxidative stress markers such as SOD, MDA, and glutathione and improve spatial learning and memory.

On the other hand, green tea could inhibit the formation of Aβ plaques and Tau, thereby reversing the cognitive impairment of animals. In this study, we selected the seven classic markers both in the two aspects to be detected, adding new evidence to the mechanism demonstration from a clinical perspective.

In terms of anti-oxidative stress, our results were consistent with the past. The intervention of green tea reduced the cytotoxicity of MDA and increased the levels of SOD, GPx, and GR, which were pretty important enzymes to protect the structure and function of cell membranes from damage, indicating that green tea improves the ability to resist oxidative stress.

Oxidative stress, which occurs when there is an imbalance between oxidant and antioxidant levels in the cell resulting in increased ROS production, is another important metabolic facet of AD pathology.

Specifically, increased levels of ROS cause damage to macromolecules within the cell, and it is this damage of lipids, proteins, and nucleic acids that gives rise to pathological consequences. In the brain, ROS are eliminated by the free radical scavenger glutathione GSH through a chemical reaction that converts GSH to its oxidized state.

As such, higher intracellular GSH levels protect cells from ROS-mediated insults. Therefore, regular green tea consumption may improve cognitive function by increasing antioxidant capacity. And the higher the levels of consumption, the stronger the correlation for this mechanism. A possible explanation is that though the content of Aβ 40 is higher than Aβ 42 in human cerebrospinal fluid and blood, Aβ 42 has stronger toxicity and is easier to aggregate, thus forming the core of Aβ plaques and triggering neurotoxic effects.

So, the sensitivity to drugs or interventions is higher than Aβ It can also be seen from existing research that the mechanism of green tea was more suited to Aβ For example, a molecular dynamics simulation experiment reported that EGCG could change the shape of Aβ 42 through hydrogen bond interactions, damage its molecular dynamics and thereby disrupt Aβ 42 protofibril Zhan et al.

Animal experiments have also revealed that EGCG significantly improved cognitive impairment in aged rats and reduced the formation of Aβ 42 plaques in the brain Wei et al. In addition, serum pTau demonstrated its potential as an early AD marker once again.

It was first discovered that there was an association between serum pTau and green tea consumption, which also provides new ideas for our future research. In short, regular consumption of green tea may affect the formation of Aβ and Tau and thus protect cognition. In the meanwhile, it has been reported that oxidative stress plays a key role in the pathogenesis of AD.

Antioxidants are compounds that have the ability to counteract the oxidative damage conferred by ROS. Therefore, the antioxidant therapy may provide benefits and halt the progress of AD to advance stages by counteracting neuronal degeneration Walia et al.

In conclusion, our study explored the relationship between green tea consumption and cognitive function among middle-aged and elderly people in China, as well as its anti-AD and oxidative stress effects. First, we comprehensively reflected on the green tea habits by inquiring about the frequency, the volume, and the years of consumption, and the subjects were divided into several groups accordingly.

Next, the cognition assessment was more diversified. MoCA was used for overall screening that is more sensitive to MCI than the Mini-Mental State Examination scale. The battery of scales covered five prime domains including memory, language, attention, executive function, and visual space.

And the influence of anxiety or depression was also excluded. Moreover, we converted the results of basic research into clinical evidence in the analysis of blood markers and the detection indicators were more comprehensive.

Finally, maybe in contrast to Eastern and Western culture and diet patterns, most orientals are accustomed to long-term green tea consumption, in comparison to coffee in the West.

Among the subjects of this study, the average consumption duration in the tea-consuming group was Consequently, the results of our study that green tea consumption was associated with better cognitive function may also be related to the years, adding new evidence to the argument for this issue.

The present study has some limitations. It was a cross-sectional study but determining the impact of diet on cognitive function is a long process.

Our findings must be validated in a long-term follow-up study.