Table 1. Characteristics of included studies in the systematic review and meta-analysis.
| Study | Country | Study design | Sample size | Mean age (years) | Follow-up duration (years) | Exposure variable | Disease type | Disease ascertainment | Adjustment |
|---|---|---|---|---|---|---|---|---|---|
| Broe et al, 1990 | Australia | Case-control | 340 | 77.5 | - | All tea | AD | NINCDS-ADRDA | Age, sex and the general practice of origin |
| Chen et al, 2012 | China | Prospective nested case-control study | 5691 | 89.2 | 3 | All tea | Cognitive decline | MMSE | None |
| Dai et al, 2006 | The United States | Cohort | 1589 | 71.8 | 6.4 | All tea | AD | NINCDS-ADRDA | Years of education, gender, regular physical activity, BMI, baseline CASI score, olfaction diagnostic group, total energy intake, intake of saturated, monounsaturated, and polyunsaturated fatty acids, ApoE genotype, smoking status, alcohol drinking, supplementation of vitamin C, vitamin E, and multivitamin, tea drinking, fruit and vegetable juice drinking, dietary intake of vitamin C, vitamin E, and β-carotene. |
| Eskelinen et al, 2009 | Finland | Cohort | 1409 | 50.2 | 21 | All tea | Dementia, AD | MMSE, DSM-IV and NINCDS-ADRDA | Age, sex, education, follow-up time, community of residence, midlife smoking, systolic blood pressure, serum total cholesterol, BMI, and physical activity. |
| Forster et al, 1995 | The United Kingdom | Case-control | 218 | 55.9 | - | All tea | AD | NINCDS-ADRDA | None. |
| Huang et al, 2009 | China | Cross-sectional | 681 | 93.5 | - | All tea | Cognitive impairment | MMSE | Age, sex, sleep habits, educational level, religion habits, and temperament. |
| Kitamura et al, 2016 | Japan | Cross-sectional | 1143 | 68.9 | - | All tea; green tea | Cognitive impairment | MMSE | Age, BMI, history of stroke, history of myocardial infarction, walking time, alcohol intake, and fruit consumption. |
| Kuriyama et al, 2006 | Japan | Cross-sectional | 1003 | 74.7 | - | All tea and green tea | Cognitive impairment | MMSE | Age, sex, energy intake, intake of nondietary vitamin C or E, fish consumption, green or yellow vegetable consumption, mild leisure-time physical activity, vigorous leisure-time physical activity, smoking, and alcohol use. |
| Lindsay et al, 2002 | Canada | Cohort | 4088 | 73.3 | 5 | All tea | AD | DSM-IV | Age, sex, and education. |
| Ng et al, 2008 | Singapore | Cross-sectional | 2607 | 66 | - | All tea; green tea; black and oolong tea | Cognitive impairment, cognitive decline | MMSE | Age, sex, education, smoking, alcohol consumption, BMI, hypertension, diabetes, heart disease, stroke, depression, APOEε4, physical activities, social and productive activities, vegetable and fruit consumption, fish consumption, and coffee consumption. |
| Noguchi-Shinohara et al, 2014 | Japan | Cohort | 490 | 71.2 | 4.9 | Green tea; black tea | Dementia, cognitive decline | MMSE, CDR and DSM-III-R | Age, sex, history of hypertension, diabetes mellitus, typerlipidemia, education, APOE ε4 carrier status, alcohol drinking, smoking, physical activities and/or hobbies, and coffee consumption. |
| Shen et al, 2015 | China | Cross-sectional | 9375 | 70 | - | All tea; green tea | Cognitive impairment | CCM and MMSE | Age, sex, race, education, marriage, tea concentration, tea categories, physical examinations, family status, disease situation, behavioral risk factors, dietary intake, nutrition supplement, depression and ADL. |
| Tomata et al, 2016 | Japan | Cohort | 13645 | 73.8 | 5.7 | Green tea; black tea; oolong tea | Dementia | LTCI system and cognitive function score | Age, sex, history of disease, educational level, smoking, alcohol drinking, BMI, psychological distress score, time spent walking, social support, participation in community activities, motor function score, consumption volume of specific foods coffee consumption, and energy intake. |
| Wang et al, 2014 | China | Cohort | 223 | 70.9 | 2 | Green tea | Cognitive decline | MMSE | Age and gender. |
| Wang et al. 2016 | China | Cross-sectional | 1005 | 72.7 | - | All tea | Cognitive impairment | Clinical diagnosis and MMSE | Not mention. |
| Wu et al, 2011 | Taiwan | Cross-sectional | 2119 | 73.3 | - | All tea | Cognitive impairment | MMSE | Age, gender, educational level, marital status, social support, hyperlipidemia, stroke, physical function, depressive symptoms, self-rated health, cigarette smoking, leisure-time physical activity, fruits and vegetables consumption, coffee intake, multivitamin intake, and BMI. |
| Yao et al, 2010 | China | Cross-sectional | 2809 | 70.6 | - | All tea | Cognitive impairment | MMSE | None. |
Abbreviations: AD, Alzheimer's disease; ADL, Activities of Daily Living; BMI: body mass index; CASI, Cognitive Abilities Screening Instrument; CDR, Clinical Dementia Rating Scale; DSM-III-R, Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; LTCI, Long-term Care Insurance; MMSE, Mini-Mental State Examination; NINCDS-ADRDA, National Institute of Neurological and Communicative Diseases and Stroke-Alzheimer Disease and Related Disorders Association.