Habitual tea drinkers may develop ASCVD 1.41 years later or die 1.26 years later than those who never or seldom drank tea, according to researchers from China.
The study indicates that tea being a popular beverage in Asia may be a healthy beverage for primary prevention against ASCVD and premature death, especially where CVD accounted for 40% of deaths in China in 2017.
There is currently no study in China that assessed the effects of habitual tea consumption on different CVD outcomes in the same population before, hence researchers conducted a nationwide study from the China-PAR project.
The study was published in the European Journal of Preventive Cardiology.
The study recruited 100,902 Chinese adults from the three cohorts: China Multi-Center Collaborative Study of Cardiovascular Epidemiology (China MUCA), International Collaborative Study of CVD in Asia (InterASIA), and Community Intervention of Metabolic Syndrome in China & Chinese Family Health Study (CIMIC).
They were enrolled in 1998, 2000-2001, and 2007-2008 and followed up at least once before 2015.
Questionnaires were used to asses tea consumption habit at baseline and during follow-up visits.
Participants were classified as habitual tea drinkers (≥3 times/week) and never or non-habitual tea drinkers (<3 times/week). Types of tea included in the study were green, black, and others except non-Camellia sinensis teas.
Participants’ body weight, height, and blood pressure data were collected. Their blood specimens were also collected to measure glucose and lipid levels.
ASCVD was defined as the first occurrence of nonfatal acute myocardial infarction (AMI), or CHD death or fatal or non-fatal stroke.
Mortality outcome was identified by interviewing participants’ proxies, checking hospital records and/or death certificates.
Longer, healthier life
Compared with never or non-habitual tea drinkers, the hazard ratio (HR) among habitual tea drinkers was 0.80, 0.78, and 0.85 for ASCVD incidence, ASCVD mortality, and all-cause mortality, respectively.
Habitual tea consumption was associated with greater disease-free years and greater life expectancy. For instance, habitual tea drinkers have 1.41, 0.32, and 1.23 years of delay in developing ASCVD, CHD, and stroke compared with never or non-habitual tea drinkers, and their life expectancy was 1.26 years longer at the index age of 50 years.
Participants who maintained their habit of tea consumption had much lower risks of ASCVD (HR, 0.61, ASCVD mortality (HR, 0.44) and all-cause mortality (HR, 0.71) compared to never or non-habitual tea drinkers.
Green tea is best
The study found that of all habitual tea drinkers, 49% consumed green tea most frequently, 43% preferred scented tea or other types, and 8% preferred black tea.
No significant association was observed for black tea while consumption of other types of tea were found to reduce the risk of ASCVD, stroke, and all-cause mortality.
Researchers explained: “Tea polyphenols might be oxidised into pigments and inactivated during fermentation, which might be partly the reason why black tea was prone to be less associated with health benefits in many studies.”
The researchers said tea, especially green tea, is a rich source of flavonoids including epicatechin, catechin, and epigallocatechin-3-gallate (EGCG).
They wrote in the report: “Mechanism studies have revealed that these bioactive compounds could attenuate oxidative stress, relieve inflammation, enhance endothelial and cardiomyocyte function. Studies in rat models showed that tea extracts could reduce the formation of vascular reactive oxygen species and improve endothelium-dependent relaxation in the aorta; and could reduce the solubility of cholesterol in micelles and inhibit cholesterol absorption from the intestine.”
In addition, observational studies and randomised controlled trials (RCTs) have also suggested that these bioactive compounds could ameliorate CVD risk factors including hypertension and dyslipidemia.
Generalised Chinese data
The researchers acknowledged some limitations in their study.
First, the findings for different tea types should be interpreted with caution, as results might have been contaminated by participants habitually consuming more than one type of tea and the proportion of black tea consumers was limited.
In addition, tea consumption is part of a cultural heritage, and its health effects might be confounded by other eating and drinking patterns, for example, consumption of other flavonoid-rich foods or beverages like coffee. “Thus, our results from the current study population might be generalisable to the general Chinese adults or other East Asia populations with similar dietary pattern and tea drinking habits but not for the West,” researchers said.
They added that further RCTs with clinical CVD events as outcomes were needed to provide robust evidence in order to develop dietary guidelines and make lifestyle recommendations.
In conclusion, habitual tea consumption could reduce the risk for both ASCVD morbidity and mortality, as well as all-cause mortality in China, and long-term adherence to the habit could provide with stronger protections.
Source: European Journal of Preventive Cardiology
“Tea consumption and the risk of atherosclerotic cardiovascular disease and all-cause mortality: The China-PAR project”
Authors: Xinyan Wang, et al.