Study Preview
Study Title and Description
Green tea consumption in everyday life and mental health.
Key Questions Addressed
| 1 | For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on behavior*? |
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Primary Publication Information
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| Title | Green tea consumption in everyday life and mental health. |
| Author | M Shimbo,K Nakamura,H Jing Shi,M Kizuki,K Seino,T Inose,T Takano, |
| Country | |
| Year | 2005 |
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Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Behavior - Design Details - INCLUDED Studies
Arms
No arms have been defined in this extraction form.
| Question... Follow Up | Answer | Follow-up Answer | |
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| Refid | 16372926 |
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| What outcome is being evaluated in this paper? | Behavior |
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| What is the objective of the study (as reported by the authors)? | The present study examined whether green tea consumption in everyday life in Japan is associated with positive mental health. |
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| Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods) | Study population A cross-sectional study was performed in February–March 2002. Of the 600 subjects, the response rate was 64.5% (n ¼ 387) and the number of completed questionnaires was 380 (63.3%). The distribution of respondents aged 20–29, 30–39, 40–49, 50–59 and 60–69 years was 13.9, 20.5, 21.8, 23.9 and 19.7%, respectively. Measurements Trained interviewers conducted 387 interviews. The interviews were performed using a standardised questionnaire. It consisted of the following categories of questions: consumption of brewed or instant green tea, coffee, black tea and oolong tea; thoughts about drinking green tea; mental health status; demographics; health status and lifestyle. The frequency of brewed tea consumption was established according to four categories (less than 1 cup per day, 1–2 cups per day, 3–4 cups per day, and more than 5 cups per day). The total daily caffeine intake was calculated based on the amount of tea (green tea, black tea and oolong tea) and coffee consumed, both brewed and instant. Estimated caffeine content in one cup (150 ml) is as follows: green tea and oolong tea, 30 mg; black tea, 45 mg; and coffee, 90 mg. Mental health status was assessed using a Japanese version of the 12-item General Health Questionnaire (GHQ 12)31. The GHQ 12 is often used in general practice as a screening tool for assessing mental ill-health32. Responses to each item were coded on 0–0–1–1. A GHQ score is obtained by summing up all items, which results in an integer from 0 to 12. Mental ill-health was defined when GHQ score was equal to or greater than 4. Statistical analysis was performed using SPSS forWindows, version 11.5 (SPSS Inc., Chicago, IL, USA). A P-value of ,0.05 was considered statistically significant. Analyses were conducted for area and gender separately. Oneway analysis of variance was used to compare the amount of daily caffeine intake from green tea, coffee and other caffeine-containing beverages among each of four levels of perceived mental stress, and a post hoc test (Dunnett’s T3) was performed if the overall difference was significant. Bivariate association of brewed green tea consumption with mental health-related indicators was tested using Spearman correlation. The independent contributions of brewed green tea consumption to the absence ( = 0) or presence ( = 1) of mental ill-health were estimated by multivariate logistic regression. To explore the potential influence, adjustment for confounding factors was developed in a stepwise manner. Age and area were first controlled for, and confounders selected by previous bivariate analyses were then added. Daily caffeine intake was finally entered to clarify the independent effects of theanine from daily consumption of brewed green tea. Odd ratios (OR) and 95% confidence interval (CI) were used to indicate the protective or risk effects on mental ill-health. |
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| How many outcome-specific endpoints are evaluated? | 2 |
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| What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) | risk of ill mental health |
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| List additional health endpoints (separately). |
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| List additional health endpoints (separately) |
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| Notes |
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| Clinical | Clinical |
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| Physiological |
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| Other |
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| What is the study design? | Cross-sectional |
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| Randomized or Non-Randomized? |
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| What were the diagnostics or methods used to measure the outcome? | Subjective |
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| Optional: Name of Method or short description | Mental health status was assessed using a Japanese version of the 12-item General Health Questionnaire (GHQ 12)31. The GHQ 12 is often used in general practice as a screening tool for assessing mental ill-health32. Responses to each item were coded on 0–0–1–1. A GHQ score is obtained by summing up all items, which results in an integer from 0 to 12. Mental ill-health was defined when GHQ score was equal to or greater than 4. |
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| Caffeine (general) | Caffeine (general) |
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| Coffee |
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| Chocolate |
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| Energy drinks |
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| Gum |
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| Medicine/Supplement |
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| Soda |
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| Tea |
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| Measured |
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| Self-report | Self-report |
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| Children |
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| Adolescents |
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| Adults | Adults |
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| Pregnant Women |
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| What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) | high vs low consumption of caffeine |
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| What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods) | age, area, perceived mental stress, lifestyle and brewed green tea consumption |
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| Provide a general description of results (as reported by the authors). | Daily caffeine intake (per 100 mg) showed a significant influence on mental ill-health status among females after adjustments for age, area, perceived mental stress, lifestyle and brewed green tea consumption were made (OR = 1.26, 95% CI= 1.01–1.56, P = 0.04). However, this association was not found among males (OR = 0.74, 95% CI = 0.53–1.05, P = 0.09). Caffeine intake reduced mental ill-health among males but increased mental ill-health among females. The mean daily caffeine intake was not significantly different by gender, being 253.0 and 271.1mg for males and females, respectively. Male subjects who reported high levels of stress ingested on average 331.3mg of total caffeine per day. This was significantly higher than for male subjects who reported no stress, with a daily caffeine intake of 212.0 mg (P < 0.05). The pattern of caffeine intake from green tea, coffee and other caffeine-containing beverages in relation to perceived mental stress was similar between males and females. Both male and female subjects who reported no perceived stress obtained most of their daily caffeine from the consumption of green tea. No overall difference in caffeine intake from green tea or coffee could be found among the four stress levels in both genders. |
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| Did the authors perform a dose-response analysis (or trend/related analysis)? | No |
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| What were the authors's observations re: trend analysis? |
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| What were the author's conclusions? | Daily caffeine intake, inclusive of green tea, black tea, coffee and other caffeine-containing beverages, was associated with a higher risk of mental ill-health among females. |
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| What were the sources of funding? | This study was supported by Grants-in-Aid for Scientific Research by the Japanese Ministry of Education, Science, Culture and Sports. |
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| What conflicts of interest were reported? | No author has any conflict of interest. |
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| Does the exposure (dose) need to be standardized to the SR? | No |
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| Provide calculations/conversions for the exposure based on the decision tree in the guide (for all endpoints/exposure levels of interest). |
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| List all the endpoint(s) followed by the dose (mg) which will be used in comparison to Nawrot. Characterize value as LOAEL/NOAEL, etc. if possible. | mental ill-health - LOAEL ≥ 100 mg/day stress (high stress) - LOAEL = 331.3 mg/day |
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| Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot. | adverse effect on mental ill-health occurs in females only adverse effect on stress occurs in males only and is based on a comparison with males reporting no stress consuming 212 mg/day |
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| What is the importance of the study with respect to the adverseness of the outcome? | Important |
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Baseline Characteristics
No baseline characteristics have been defined for this extraction form.
Results & Comparisons
No Results found.
Adverse Events
| Arm or Total | Title | Description | Comments |
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Quality Dimensions
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Quality Rating
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