Originating in China, the consumption and planting of tea (Camellia sinensis, Theaceae) has spread in popularity, with more than 160 countries in the world today being accustomed to tea drinking. This makes the drinking of tea one of the most widely consumed beverages globally. Tea is one of the most popular and cost effective beverages consumed after water, renowned for its health promoting properties since ancient times. Black (aerated), green (non-aerated) and oolong (partially aerated) tea are three of the most popular tea forms consumed today, all of which are produced from the leaves of the plant Camellia sinensis. Alongside this, the market and evidence-based for tea forms other than black and green tea is growing, including chamomile, sour, hibiscus, goishi and rooibos tea.
So, what is cardiovascular disease?
Cardiovascular Disease (CVD) encompasses a range of disorders of the heart and blood vessels. More people die annually from CVDs than from any other cause making this the number one cause of death globally.
Investigating the link between tea drinking and the reduction of CVD
There has been a significant upsurge in the number of scientific articles studying the role of tea in human health. A large body of observational evidence has made links between tea consumption and reduced risk of heart disease alongside other factors such as reduced stroke risk, particularly ischaemic stroke. A number of new randomised controlled trials (RCTs) have been published within this field in recent years. We collated the results of meta-analysis studies and RCTs published in the last 10 years and the effect of tea consumption on measures of CVD was considered.
- Findings from 19 meta-analysis and 23 randomised controlled trials (n=1,422 participants) were evaluated.
- Moderate evidence was of a positive effect of green tea and its associated catechins on total and low density lipoprotein (LDL) reduction.
- Growing evidence indicates that tea drinking could protect vascular health and reduce inflammation.
- A wider range of tea forms (chamomile tea, goishi tea, hibiscus tea, sour tea, rooibos tea) are increasingly being studied and also appear to have potentially favourable effects on markers of CVD.
- Regular consumption of black and green tea was associated with reductions in blood pressure which could be important for CV health at population level.
- Strong evidence from meta-analysis that long-term consumption (<12 weeks) and drinking 4-5 cups tea (green and black) daily could reduce systolic and diastolic blood pressure, especially those in pre- and hypertensive ranges.
- There is emerging meta-analytical evidence that sour tea may reduce systolic and diastolic blood pressure.
- Growing evidence from RCTs that drinking 2-3 cups black tea may also reduce systolic and diastolic blood pressure.
- Three further RCTs show that sour tea may reduce blood pressure, especially amongst type 2 diabetics.
- One RCT showed that brewed hibiscus tea daily significantly lowered blood pressure amongst pre- and mildly hypertensive adults.
Given the high prevalence of hypertension in the UK, and worldwide, these findings have important public health implications. A large proportion of the general population have blood pressure levels within the ranges included in trials, showing they are at increased risk of hypertension and hence these results are particularly applicable.