Black Tea May Lower Blood Pressure
Coffee, red wine, and green tea, take note: Black tea may be joining you on the list of drinks that could have health benefits – at least this week.
A small study published Jan. 23 in the Archives of Internal Medicine shows that people who consumed 3 cups of black tea daily over a 6-month period had a 2-3 mm Hg drop in their systolic and diastolic blood pressures. The drop is significant, according to Jonathan M. Hodgson, Ph.D., and his colleagues at the University of Western Australia in Perth.
Of course, there have been numerous instances of studies of nutrients or botanicals that have yielded much less exciting results when conducted as a large-scale trial.
But if further studies show that black tea has such a positive effect on blood pressure, its regular consumption could reduce the prevalence of hypertension by 10% in a population, and lead to “7% to 10% reduction in the risk of cardiovascular disease,” they write.
Although polyphenols like flavonoids have been studied extensively, none of the studies has looked at the effect of black tea on blood pressure, the authors note. Black tea packs as many flavonoids as green tea, but the fermenting process produces a different mix of the powerful anti-oxidants.
The researchers conducted a randomized, placebo-controlled double-blind study of 95 participants. (There were 18 men and 31 women in the placebo group, and 15 men and 31 women in the tea group.) Their ages ranged from 35 to 75 years; their body mass indexes were between 19 and 35; and their daytime ambulatory systolic blood pressure was between 115 and 150 mm Hg. Energy and nutrient intake and body weight did not differ between the placebo and tea groups, nor did they vary much during the study’s 6 month period.
Participants in the tea group consumed 3 cups daily of 1,493-mg powered black tea solids that contained 429 mg of polyphenols and 96 mg of caffeine, the authors report. The placebo group got a drink that matched the flavor and caffeine content, but had no tea solids.
The net results showed that systolic blood pressure of the tea group dropped by 2.7 mm Hg after 3 months, and 2 mm Hg after 6 months.
On the basis of 24-hour ambulatory monitoring performed at baseline and at 3 and 6 months, their diastolic blood pressure dropped by 2.3 mm Hg after 3 months, and 2.1 mm Hg after 6 months.
So how do the authors explain their findings?
One mechanism could be improvements in endothelial function. One meta-analysis that showed that flow-mediated dilation of the brachial artery can be improved by tea consumption (PLoS One 2011;6:e16974). In another study conducted by Dr. Hodgson and his colleagues, tea flavenoids augmented nitric oxide status and reduced endotheline-1 levels in 12 healthy men (Am. J. Clin. Nutr. 2008;88:1018-25). This effect could reduce the vascular tone and lower the blood pressure, the authors note.
Or, part of the answer may lie in the effect of tea flavonoids on body fat, and more specifically, abdominal fat. (The authors note that there was no significant effect on the participants’ body weight during the study period.)
It’s not quite clear how much polyphenols/flavonoids Americans consume in their daily diet, with estimates ranging from 200 mg to 1 g per day. Meanwhile there are databases that list the polyphenol content of foods, including Phenol-Explorer.
If the findings of this study are confirmed in larger trials, maybe more people would be encouraged to consume this ancient drink, maybe a coffee shop chain will come up with a fancy fusion, and maybe there will be a pill. But one thing is for sure: Regardless of the findings, that kettle or samovar of hot tea will continue to simmer in a home somewhere in the continent of Asia, to be savored morning, noon, afternoon, and night.
The authors reported no financial conflicts. The study was funded by the National Health and Medical Research Council of Australia, and Unilever Research and Development, Vlaardingen, the Netherlands.
---Naseem S. Miller (on Twitter @NaseemSMiller)