Drinking black tea may have health benefits and even prolong one's life, says a new study from the National Institutes of Health. Photo by Wiro Klyngz/Shutterstock
Aug. 29 (UPI) -- Coffee drinkers take heed: People who drink black tea daily had lower risk for death than non-tea drinkers over more than a decade of follow-up, a new study says.
The risk was lowest -- 9% to 13% -- among people who had two or more cups of black tea per day, according to the research from the National Cancer Institute.
And drinking tea -- one of the most consumed beverages worldwide -- had a beneficial effect on mortality regardless of whether the study's participants also drank coffee, and regardless of genetic variation in their caffeine metabolism.
The findings were published Monday in Annals of Internal Medicine.
"The study cannot definitively prove that tea drinking directly reduced the risk for death during the follow-up period," the NCI researchers said in a summary of the findings. "However, these findings provide reassurance to tea drinkers and suggest that black tea can be part of a healthy diet."
Despite this, Maki Inoue-Choi, the study's corresponding author and an epidemiologist in NCI's Division of Cancer Epidemiology & Genetics, told UPI that "Results from a single study should not by themselves be used to determine whether people should start drinking tea or change the amount they drink."
Previous studies have suggested a modest mortality benefit associated with tea drinking, but it's been largely been observed in populations in which green tea drinking is common.
So, the scientists investigated the association of black tea consumption with all-cause and cause-specific mortality in the United Kingdom, where black tea drinking is common. Findings on this brew's potential benefits have been inconsistent to date.
The researchers found that with higher intake, risks for death from cardiovascular disease, ischemic heart disease and stroke lessened, but not from cancer.
The study involved nearly half a million men and women ages 40 to 69 who participated from 2006 to 2010 in the U.K. Biobank, a large-scale biomedical database used for international research.
Information on death and primary cause of death among the study's participants was obtained from a linked database under the U.K. National Health Service. Nearly 30,000 deaths occurred over the 14-year follow-up period, averaging 11 years.
The investigators said potentially confounding factors, including age, sex, race and ethnicity, education, body mass index, general health status, co-morbid conditions, smoking, physical activity, alcohol drinking, coffee consumption and diet, including fruits, vegetables and red meat, were assessed at baseline.
The study's participants completed dietary questionnaires upon enrollment and during follow up about their tea-drinking habits: how many cups of tea of any kind they drank daily, and at what temperature they liked to drink tea, from very hot to warm.
"We assessed whether a risk of death among tea drinkers differs by reported tea temperature, because drinking very hot tea has been associated with an increased risk of esophageal cancer," Inoue-Choi said in an email. "But drinking tea was not associated with increased risk of death regardless of tea temperature."
Overall, 85% of participants in the U.K. Biobank study reported tea drinking, and among a subset who reported tea type, 89% reported consuming black tea and 7% drank green tea. More than 9 of 10 participants self-reported as being White.
The scientists drilled down to seemingly small factors, such as the participants' use of milk and sugar as common additives to tea, and steeping time.
But they conceded there might be "unmeasured factors" that could be associated with both tea-drinking behavior and the risk for death.
They also noted their analysis did not assess potentially important aspects of tea intake, such as portion size and tea strength.
Yet, the investigators also cited several strengths of the study, including its large sample size and extended follow-up period.
Inoue-Choi said one aspect of the study was surprising.
"We were surprised to see a wide range of tea consumption with some individuals reporting drinking 10 or more cups per day," she said. "We were also surprised that the associations were seen regardless of milk or sugar use in tea and preferred tea temperature."
She added: "People still should follow dietary guidance on limiting sugars and saturated fat for chronic disease prevention."