This study was conducted with young adult interviewees aged 18-24. Subjects were selected by simple random sampling. The 100 questionnaires were distributed face-to face in several education institutes including The University of Hong Kong, HKU SPACE Po Leung Kuk Community College and The Hong Kong Polytechic University in March 2014. Most of the respondents are students in those institutes. Approval was obtained from the Human Research Ethics Committee for Non-Clinical Faculties, the University of Hong Kong and the written informed consent forms were given to volunteers at the beginning of the study.
The questionnaire consists of four sections including basic information, green tea drinking habit, knowledge about health effects of green tea and self- described health condition. The sample was composed of 100 individuals who finished the questionnaires including demographic and lifestyle factors. Moreover, the participants were also asked habitual green tea consumption such as the frequency of drinking green tea, the number of cups of green tea they drink, the drinking time slot and the drinking method. In addition, the interviewees answered questions regarding subjective sleeping quality and time of sleeping and waking up. A question on problems related to sleeping quality was included.
The subjects were classified into groups by male and female, green tea drinkers and non-green tea drinkers, as well as by different drinking method including tea leaves, tea bag, bottle drink and tea powder. Respondents were separated into different groups according to their consumption amount, low (≤ 4 cups which is a median) versus high dose (> 4 cups) in the questionnaire. The consumption amount was calculated as frequency (question 12) multiplied by dosage (question 13). The green-tea drinkers were categorized into poor sleeper (score<3) and good sleeper (score≥3) so as to study the effect of drinking time. Group differences were analyzed using the student t-test, which was run to analyze the associations between the green tea drinking factors and sleep parameters such as sleep duration and subjective sleep quality. Sleep duration was calculated as the upper bandings of waking up time subtracted from that of sleep onset (For the last options of question 4 and 5, the upper bandings are 2 am and 11 am respectively). All the analyses were carried out using Microsoft Excel software.
Table 1. Differences in the demographic characteristics between green tea and non-green tea drinkers
Predictors Green tea drinkers (n=64) Non-green tea drinkers (n=36)
Gender Male 23 24
Female 41 12
Age 19.94± 1.308 20.08± 1.381
A total of 100 interviewees finished the questionnaire (response rate: 100/100= 100%). This consisted of 47 males (47%) and 53 females (53%) with a mean age of 19.9(range, 17 to 24 years; SD, ±1.3) as showed in Table 1. There was no difference between green tea drinkers and non-tea drinkers in age,...