Drinking tea has several reported health benefits, but most studies have been conducted in regions where green tea predominates.
The findings come from a prospective study of nearly 500,000 participants in the UK Biobank cohort, among whom drinking black tea was common. They suggest that drinking black tea may be associated with a moderately lower all-cause mortality risk, and the risk was lowest among those drinking two or more cups of tea per day.
The study was published online in Annals of Internal Medicine.
During a median follow-up of 11.2 years, those who drank at least two cups of tea each day had a lower all-cause mortality risk, reported Maki Inoue-Choi, PhD, and colleagues from the National Cancer Institute in Bethesda, Md.
After multivariate adjustment, the hazard ratios for death among tea drinkers, compared with no tea intake, were similar across intake levels: 0.95 for daily intake of up to 1 cup, 0.87 for 2-3 cups, 0.88 for 4-5 cups, 0.88 for 6-7 cups, 0.91 for 8-9 cups, and 0.89 for 10 or more cups.
Drinking tea also showed an inverse association with mortality from cardiovascular disease (adjusted HRs ranging from 0.98 to 0.76), ischemic heart disease (aHRs ranging from 1.03 to 0.74), and stroke (aHRs ranging from 0.92 to 0.48 ), However, the researchers added that “no clear trend was seen for cancer or respiratory disease mortality, with associations among higher intake categories tending toward the null.”
There is “no clear answer” as to why no association was observed between tea consumption and cancer mortality in the current study, Dr. Inoue-Choi said at a press briefing. Notably, the effects were apparent regardless of whether milk or sugar was added to tea, tea temperature, or genetic variations in caffeine metabolism among participants.
She and her colleagues controlled for these factors, as well as numerous others that could confound the results, including coffee consumption and baseline health and demographic characteristics..
The study subjects were 498,043 adults with a mean baseline age of 56.5 years. About 85% reported drinking tea, 90% reported drinking black tea, and most drank two to three cups (29%), four to five cups (26%), or six to seven cups (12%) per day.
A limitation of the study is the lack of information on certain aspects of tea intake, such as portion size and tea strength, the authors noted.
Tea is among the most frequently consumed beverages worldwide, and studies from places where green tea is popular, like China and Japan, have demonstrated health benefits. Data from places where black tea is more commonly consumed have been lacking and have provided conflicting results, Dr. Inoue-Choi said.
A presumed mechanism of action related to tea consumption is reduced oxidative stress and inflammation thanks to "polyphenols and flavonoids, namely catechins and their oxidated products," the authors explained. Oxidative stress and inflammation may promote carcinogenesis; therefore, reducing oxidative stress and inflammation may improve endothelial function, they added.
“While these findings may offer reassurance to tea drinkers, they do not indicate that people should start drinking tea or change their tea consumption for health benefits,” Dr. Inoue-Choi said, explaining that “the results need to be replicated in future studies and extended in other diverse populations.”
This study was funded by the National Cancer Institute Intramural Research Program and the NCI division of cancer epidemiology & genetics. The authors reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.
This article was updated 8/31/22.