Association between tea consumption and cognitive impairment in middle-aged and older adults

The Asymptomatic Polyvascular Abnormalities in Community (APAC) study is a cross-sectional, community-based, and observational investigation designed to explore the epidemiology of asymptomatic polyvascular abnormalities in Chinese adults. The APAC study population was a part of the previously described Kailuan cohort [16, 17], with 101,510 participants (18–98 years old). In 2010, 7000 participants aged over 40 were randomly selected from the Kailuan study by a random sampling method stratified by age and sex. A total of 5852 people agreed to take part in the APAC study, and eventually, 5816 participants completed the baseline data collection. Three hundred seventy-six participants who did not meet the inclusion criteria were excluded. The inclusion criteria of the APAC study were: (i) over the age of 40; (ii) no history of transient ischemic attack, stroke, or coronary heart disease supplied by participants or their legal representatives at baseline interview; and (iii) absence of neurologic deficits for the previous stroke examined by experienced clinicians. A total of 5440 participants were finally eligible in the APAC study. In this study, information about tea intake and cognitive assessment were collected, and participants were divided into two subgroups for statistical analyses according to cognitive function evaluation methods. We further excluded participants without information of tea consumption (n = 1503), results of Mini-Mental State Examination (MMSE) test (n = 38) or Montreal Cognitive Assessment (MoCA) (n = 3119), and complete data (n = 31, for MMSE group; n = 12 for MoCA group), leaving 3868 and 806 participants included in MMSE and MoCA subgroups, respectively (Fig. 1). According to the Helsinki Declaration, this study was performed and was approved by the Ethics Committees of Beijing Tiantan Hospital and Kailuan General Hospital.

MMSE and/or MoCA measured cognitive. MMSE is one of the most common and popular cognitive status measurements, but it has a ceiling effect to identify mild cognitive impairment [18]. However, compared to MMSE, MoCA includes more cognition domains tests and presents higher sensitivity and specificity for evaluating early and mild cognitive disorders [19‐22]. In this study, to confirm the results, we also used MoCA to detect mild cognitive impairment and performed the analysis. Both the total score of MMSE and MoCA is 30-points [19, 23]. An aggregate score of MoCA needs to be added 1 point when the education level is less than 12 years if the total score is less than 30-points [24]. Cognitive impairment is defined as a score of MMSE < 24 [25], or a score of MoCA < 26 [26].

We collected information about tea consumption via a standardized questionnaire. People were asked to report the habit, the average frequency, and the type of tea they consumed in the past 5 years. The habit is divided into “never” and “habitual.” For the frequency of tea consumption, we provided five choices, including “never,” “less than once/month,” “1–3 times/month,” “1–3 times/week,” and “≥ 4 times/week.” The type of tea consumption included “never,” “green tea,” “black tea,” and “other types” [27].

Standardized questionnaires collected demographic information (e.g., age and sex), level of education, lifestyle behaviors (including smoking, alcohol consumption, and physical activity), and medical history (including hypertension, diabetes mellitus, and dyslipidemia). Body mass index (BMI) was calculated as weight (kg) divided by height in meters squared (m2), and classified into three categories according to BMI levels, as “ideal: < 25 kg/m²” “intermediate: 25–29 kg/m²,” and “poor: ≥ 30 kg/m².” Physical activity was classified by the time of moderate or vigorous activity per week, as “≥ 80 min,” “1–79 min,” and “0 min.” Salt intake was categorized into “< 6 g/day,” “6–10 g/day,” and “> 10 g/day.” [17] Biochemical parameters including plasma high-sensitivity C-reactive protein (hs-CRP), fasting blood glucose, total cholesterol, triglycerides, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were measured using an auto-analyzer (Hitachi 747; Hitachi, Tokyo, Japan) at the central laboratory of the Kailuan General Hospital. Hypertension was defined as having a self-report history of hypertension, systolic blood pressure ≥ 140 mmHg, diastolic blood pressure ≥ 90 mmHg, or taking antihypertension agents. Diabetes mellitus was defined as having a self-report history of diabetes mellitus, a fasting blood glucose level ≥ 7.0 mmol/l, or treated with oral hypoglycemic drugs or insulin. Dyslipidemia was defined as the presence of a history of dyslipidemia, triglycerides level ≥ 1.7 mmol/l, total cholesterol ≥5.17 mmol/l/ [28].