In a recent study published in the Nutrition Journal, researchers investigated whether the protective effects of consuming tea against hypertension and mortality interact with alcohol intake among Chinese individuals.
Study: Alcohol intake masked the protective effects of tea consumption against all-cause mortality and blood pressure progression: Findings from CHNS cohort, 1993–2011. Image Credit: iroKlyngz/Shutterstock.com
Background
Tea is an extensively consumed beverage across the globe. Recently published studies have reported the beneficial effects of consuming tea against various medical conditions, including hypertension, cardiovascular disorders, diabetes, stroke, heart attack, and mortality.
However, several factors, such as milk content, smoking habits, coffee intake, lifestyle, and gender, could lower the health benefits of consuming tea.
Nevertheless, data on the probable interactions of alcohol and tea concerning outcomes such as hypertension and mortality are limited.
About the study
In the present large-scale, prospective cohort study, researchers investigated the association between tea intake, blood pressure (BP) changes, and death among alcohol drinkers compared to non-alcohol drinkers in China.
The study included 6,387 individuals in the China Health and Nutrition Survey (CHNS) and was conducted in the 1993-2011 period.
Individuals with two or more records of tea intake, with a minimum of one from 1993, were considered for the present analysis. The team conducted group-based trajectory modeling (GBTM) to identify distinctive long-term trajectories of tea intake over 18 years.
Data on tea intake in the preceding year, including mean cups of tea consumed daily, were obtained through in-person surveys in the follow-up rounds between 1993 and 2011. Individuals who drank alcohol in the preceding year were considered current alcohol consumers. The outcomes were death due to any cause and changes in BP readings.
In the case of mortality, family members of the deceased individuals were interviewed. The last day of life or the date of the final survey, whichever occurred earlier, was recorded to determine the duration of follow-up.
Cox regression modeling and Kaplan-Meier statistics were utilized to evaluate the cumulative mortality rate. The team used restricted cubic splines to assess the non-linearity of associations between the mean consumption of tea and death.
Generalized linear mixed-effects modeling (GLMM) was performed to evaluate BP alterations among tea intake trajectories, and the hazard ratio (HR) was determined by adjusting for covariates such as age, marital status, sex, nationality, residence, level of education, occupation, annual household income, smoking habits, comorbidities (such as diabetes, hypertension, and cancer), antihypertensive medication use, and the mean values for body mass index (BMI), waist circumference, and hip circumference.
CHNS data were obtained from 12.0 provinces through multistage, random-cluster sampling. The CHNS cohort was initiated in 1989 and followed up every two to four years from 1989 to 2015 among more than 30,000 individuals.
Results and discussion
The average age of the individuals was 54 years; 50% were male, and 33% of them drank alcohol in current times.
The participants were divided into non-tea consumers (zero cups consumed daily), light tea consumers (who drank one cup daily), and high tea consumers (who drank three to four cups daily). Among the study participants, 2,838 and 1,478 were light and high tea consumers, respectively.
After following up for 18 years (median), nine percent of participants (n=580) died. The relationship between tea intake and mortality was influenced by alcohol consumption.
The cumulative mortality rate was lower among high-tea consumers than non-tea consumers (HR 0.8). However, high tea intake lowered the mortality risk only among non-alcohol consumers (HR 0.6).
A linear tea-mortality relationship was observed for current alcohol consumers, indicating that alcohol obscured the benefits of tea against mortality. In addition, according to the GLMM modeling findings, alcohol also obscured the BP-lowering effects of tea. Similar results were obtained in the sex-stratified analyses.
Individuals consuming tea in high amounts daily were more likely to be older male smokers residing in urban locations.
Current alcohol consumers had a greater probability of having unhealthy lifestyles and smoking and higher values for BMI and waist and hip circumferences than non-alcohol drinkers, which could reduce the benefits of consuming tea.
Alcohol reportedly blunts the antioxidant activity of tea-derived polyphenols. The BP-lowering effects of drinking tea may be due to a tea-induced delay in arterial stiffness.
Conclusions
Overall, the study findings showed that three to four cups of regular tea intake lowered the risk of death and prevented increases in blood pressure. However, the benefits of consuming tea were reduced by consuming alcohol, which was, at times, even harmful to health.
The study findings underpin the beneficial effects of consuming tea on mortality, as reported by previous studies, and extend the results to a broader population in China.
However, the sample population does not represent the entire nation, and thus, the findings have limited generalizability.
Further research must analyze national data obtained from randomized controlled trials (RCTs), on tea intake, including the type of tea consumed, using objective methods.
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