I was researching nonsense claims about foods when I came across a few articles that claimed that black tea could help you lead a long life. As I am a devoted drinker of black tea (only in the iced form, I’m not British, Australian, or Indian), I was intrigued. Was this some nonsense pushed by woo quacks, or was it based on robust science?
Now, I am especially skeptical about any nutritional study that attempts to link some food to any health benefit, and most of the recent articles were mostly on quack websites that support just about anything a scientist or my loyal readers would scoff at.
As you know, I’m going to get to the bottom of this story. Is there science? Or is it just typical junk science?
What is the basis of these black tea claims?
Believe it or not, these claims about the health benefits of black tea come from a recent article in a well-respected medical journal. That’s a good start.
In an article, published on 30 August 2022 in the high impact factor Annals of Internal Medicine, Maki Inoue-Choi, Ph.D., of the National Cancer Institute in Bethesda, Maryland and colleagues reviewed data from 498,043 men and women aged 40 to 69 years who completed the baseline touchscreen questionnaire from 2006 to 2010 in the UK, which has a tea culture that puts it in the top countries in tea consumption.
According to the researchers, over 90% of the tea consumed in this group was black tea.
Here are the key results:
- Individuals who drank less than one cup per day didn’t show a statistically significant protective benefit from black tea, the hazard ratio (HR) of mortality risk = 0.95.
- Two to three cups per day — HR = 0.87 or 13% reduction in mortality risk.
- Four to five cups — HR = 0.88 or 12% reduction in mortality risk.
- Six to seven cups — HR = 0.88 or 12% reduction in mortality risk.
- Eight to nine cups — HR = 0.91 or 9% reduction in mortality risk.
- 10 or more cups — HR = 0.89 or 11% reduction in mortality risk.
I wouldn’t concentrate too much on the differences between the amount consumed, for reasons I’ll explain later.
The researchers also performed other analyses which I found interesting:
- Drinking more than two cups of tea per day was associated with a 14% to 24% lower risk for death from all cardiovascular diseases. The heaviest tea drinkers had the highest risk reduction.
- Drinking two to three cups per day was linked with a 17% lower risk of death due to ischemic heart disease. But drinking eight or more cups on average was associated with a 26% lower risk of the same.
- Those who drank 10 or more cups per day saw a significant risk reduction HR= 0.48 for stroke-related deaths.
- Those who consumed two to three cups of tea per day were also linked with a modestly reduced risk for respiratory disease-related death and cancer-related death.
Looking over this data, I would say that the data showed small and occasionally large health benefits and a reduction in mortality risk by drinking even large amounts of black tea. But! And there’s always a but.
Analysis of results
I am not a fan of these types of studies, for lots of reasons.
- They may show correlation, but they do not establish causation.
- Survey studies like this one rely upon the memory of the subjects.
- Sometimes the effects were so small that clinical significance may not exist.
- There is no standardization of what is a “cup” of tea. I’m drinking iced black tea right now, and I know the cup is much larger than a standard cup of tea.
- We do not know the concentration of tea in these cups.
- We do not know the effect of what’s added to the tea — milk, sugar, or artificial sweeteners.
- What might be the confounders that influence the results — obesity, smoking, overall diet, and other factors could influence the results? For example, someone who consumes a lot of black tea may smoke less or weigh less or eat better than someone who doesn’t drink tea. Maybe these issues mess up the data, or they may provide clarity. But I’d like to see a much more complex study that tries to show the overall health of black tea drinkers.
Now, one of the most important issues to make correlation equal to causation is biological plausibility. And there appear to be chemicals in tea that may have health benefits.
On the other hand, this research comes from National Cancer Institute researchers who published their findings in a well-respected medical journal. That doesn’t mean that we should completely buy into their results, but this is better than a lot of nonsense claims I read about foods on the internet.
There’s not a lot of research on the long-term risks of drinking a lot of black tea (and that kind of study would suffer from the same issues as this study), but it appears to be safe. Given that, I’m going to convince myself that my two large cups of black tea every day have some medical benefits.
Rating the research
I’m trying out something new (and you can criticize it in the comments if you want). I’m going with a five-star rating with a one-star rating being completely worthless research to a five-star rating being high-quality research, one of the best.
I’m going to give this study 3.5 stars (yeah, I’m cheating). It’s not convincing, but it’s better than the medium three-star level. I just don’t think it’s quite at the four-star level, but as I develop this, I might have to revisit it.
Citations
- Inoue-Choi M, Ramirez Y, Cornelis MC, Berrington de González A, Freedman ND, Loftfield E. Tea Consumption and All-Cause and Cause-Specific Mortality in the UK Biobank : A Prospective Cohort Study. Ann Intern Med. 2022 Aug 30. doi: 10.7326/M22-0041. Epub ahead of print. PMID: 36037472.
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