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Where would we be without coffee and tea? Our favorite sources of caffeine spur productivity, social connection and pleasure, and their ritual importance makes them central to many cultures. Even better, they may be fueling longer lives and reduced disease risks for people who enjoy them.
New research has linked coffee and tea to increased life spans, especially when both beverages are consumed together in moderate amounts. Past studies have linked coffee and tea, separately, to improved health, including reduced cognitive decline, stronger hearts and more. The new study, published late last year in BMC Medicine, broadens our understanding of how coffee and tea work together in the body to affect health in the long term. It also adds to the evidence that the caffeinated beverages, which have a long history of being demonized as unhealthy, can be part of a healthy lifestyle when consumed in moderation.
The researchers, from China's Tianjin Medical University, evaluated nearly 500,000 people ages 37 to 73 by analyzing roughly 12 years of data from the UK Biobank, a large biomedical database. By comparing amounts of coffee and tea consumed (both separately and together) with specific causes of death (including cardiovascular, respiratory and digestive diseases) and all-cause mortality, they were able to determine the drinking patterns that tend to be linked to the lowest rates of disease and the longest life spans.
The authors found that people who drank coffee and tea, both separately and combined, were less likely to have died during the study period, both due to specific diseases and other reported factors. For people who drank only coffee or tea, but not both, the lowest risk of overall mortality was found in those who drank around 1 cup of coffee or 3 cups of tea per day.
The interactive effects of coffee and tea together were especially strong on overall and digestive disease–related mortality. The strongest boost to life span was found with daily consumption of 2 to 4 cups of tea as well as up to 2 cups of coffee. Compared to drinking neither coffee nor tea, this daily consumption was associated with a 22 percent lower risk of death overall, plus reduced risks of death from cardiovascular disease and respiratory disease—24 percent and 31 percent lower, respectively. In people who drank 2 or fewer cups of coffee as well as at least 5 cups of tea per day, a 58 percent reduced risk of death from digestive disease was reported.
Coffee and tea drinkers who also consumed moderate amounts of alcohol experienced improved health outcomes, when compared to coffee and tea drinkers who rarely or never consumed alcohol and those who consumed high amounts of alcohol.
What explains the observed health benefits of tea and coffee? The researchers hypothesize that caffeine and chlorogenic acid may "play a crucial role in antioxidants, anti-inflammation, lowering blood pressure [and] insulin resistance and improving endothelial function,” the latter of which benefits blood flow. These effects may, in turn, prevent disease and improve overall health. Given that other studies have linked both decaffeinated and caffeinated coffee to improved health outcomes, the researchers say that other "bioactive substances in coffee and tea [may] also play a protective role." They point to multiple antioxidant compounds in coffee as well as "epicatechin, catechin ... and other flavonoids" in tea, some of which are also found in wine.
The UK Biobank questionnaire did not differentiate between types of coffee or tea, so it's unclear if there are health differences between caffeinated and decaf, drip and espresso, or green and black teas. The study also relied on self-reported data, which is prone to bias—people don't always accurately remember how much they drank, and they might change their answers to reflect how much they think they should, or shouldn't, have drank. Moreover, many of the participants in the UK Biobank are of European descent; they also tend to be more health-conscious than the general population, so it's unclear how the results apply to other demographics.
The researchers used standard statistical methods to control for potentially confounding variables: other aspects of coffee and tea drinkers' lifestyles that could explain the results, including diet, exercise, alcohol intake, smoking and more. Nevertheless, since this was an observational study, they concede the possibility that confounding or chance interactions could have skewed results, and they acknowledge that coffee and tea drinkers tend to have better baseline health to begin with.
The authors call for further study, especially to investigate the full scope of the interactions between tea and coffee when consumed together.
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