Daily tea consumption was associated with an 8% relative risk reduction in ischaemic heart disease and a 10% relative risk reduction in major cardiac events, in a large prospective study from China.

This prospective study enrolled 512,891 participants, aged 30-79 years, from five urban and five rural areas across China between 2004 and 2008. Participants were asked in a questionnaire about their frequency of tea consumption over the past

12 months, age at which they first started drinking tea, type of tea most commonly drunk (green tea, oolong tea, black tea, or others).

Tea consumption was measured in grams of tea leaves added which may be a better measure of tea consumption than number of cups.

After excluding those with cancer, heart disease and stroke at baseline, the study included 199,293 men and 288,082 women who were followed up until 31 December 2013. Data on the incidence of ischaemic heart disease were collected through disease registries and the national health insurance databases.

During a median follow-up of 7.2 years, there were 24,665 cases (7.19/1,000 person-years) of ischaemic heart disease and 3,959 cases (1.13/1,000 person-years) of major coronary events, including 2,601 cases of fatal ischaemic heart disease and 1,358 non-fatal myocardial infarctions.

Tea consumption was associated with a reduced risk of both ischaemic heart disease and major coronary events. Compared with those who had never consumed tea during the past 12 months the multivariable adjusted hazard ratio (HR) of daily tea drinkers was 0.92 (95% CI: 0.88-0.95) for ischaemic heart disease and 0.90 (95% CI: 0.82-0.99) for major coronary events.

Of those who drank tea daily most drank green tea. Similar assocations for tea consumption were seen for both green tea and non-green tea.

Increasing the frequency of drinking tea to more than once a day did not reduce the risk further.

The protective effect of drinking tea appeared to be stronger for both outcomes among participants who reported longer years of tea consumption and for those who resided in rural regions. Tea had a stronger protective effect with respect to major coronary events in those with a body mass index < 24 kg/m2, and a stronger protective effect against ischaemic heart disease in those who did not have diabetes at baseline.

There are plausible reasons for tea to be potentially protective against cardiac disease. Tea contains flavonoids, which have been experimentally demonstrated to inhibit oxidation reactions caused by free radicals and prevent or delay atherosclerosis. Flavonoids have also been shown to have anti-thrombotic and anti-inflammatory properties and may reverse endothelial dysfunction.

The authors conclude: ‘Data from this largest prospective cohort of Chinese adults showed that daily tea consumption was associated with a decreased risk of ischaemic heart disease incidence. Given the observational nature, this study alone could not establish a causal relationship. Further randomised studies may be needed to confirm the protective effect of tea consumption on ischaemic heart disease.’

Dr Peter Savill

Li X, Yu C, Guo Y et al on behalf of the China Kadoorie Biobank Collaborative Group. Tea consumption and risk of ischaemic heart disease. Heart 2017;103:783-89