Does Drinking Tea Lower Your Risk of Death? 🫖
This Week’s Research Highlight
Background
Many studies have been conducted that assess associations between tea consumption and long-term health outcomes — a few of which we have explored previously in this newsletter. And overall, the picture seems pretty positive for tea drinking.
However, many of these studies have focused on clinical samples, like patients with chronic diseases. For instance, an epidemiological study in Japan found that people with type 2 diabetes who drank four or more cups of tea per day had 40% lower odds of dying during follow-up.
These are encouraging findings, of course. But it’s hard to say whether reductions in death observed in such individuals can necessarily be applied to healthy folks. Going back to the example of type 2 diabetes. Tea has favorable effects in these patients in part because catechins in tea can inhibit enzymes responsible for breaking down carbohydrates into sugars, which in turn leads to better glycemic control. But you can imagine that the impact of this mechanism is going to be much more clinically meaningful in someone with compromised blood sugar, versus a healthy person who already has normal insulin sensitivity. There’s just not as much room for improvement in the latter case.
That’s why a brand new meta-analysis caught my eye, which specifically zeroes in on the association between tea consumption and mortality in the general population. Let’s take a look.
Study
Researchers in South Korea performed a systematic review and meta-analysis of observational studies in the general population, avoiding research performed specifically in patient groups.
In order to be included in the meta-analysis, studies had to meet the following criteria:
- Prospective cohort design
- Exposure of interest was tea consumption
- Outcomes of interest were mortality from all causes, cardiovascular disease, and/or cancer
- Researchers reported estimated effect sizes (meaning how much of an impact that tea intake had on mortality)
After applying this criteria to their search, the researchers wound up with a total of 38 prospective cohort studies from all over the globe. That included pooled data from a total of 1,956,549 participants, so we are talking about some serious statistical power here!
The mean follow-up time for these studies was 12.3 years, with duration ranging from 5 to 23 years.
These studies, generally speaking, were well-adjusted for significant potential confounders. All were adjusted for age and smoking, and most were adjusted for body mass index and alcohol consumption.
Finally, the researchers also wanted to figure out how much tea might be optimal for increasing longevity, so they performed a dose-response analysis.
Findings
Overall, compared to the lowest level of tea consumption, the highest intake was associated with a 10% lower risk of death from all causes and a 14% lower risk of death from cardiovascular disease.
How much tea was optimal? The dose-response analysis showed that the most significant reduction in all-cause mortality was seen at 2 cups per day. For cancer mortality, benefits seemed to peak at 1.5 cups per day, while risk reduction for cardiovascular mortality continued to improve up to 8 cups per day.
However, if you scan through the characteristics of the studies included in the meta-analysis, you’ll see some substantial heterogeneity.
Perhaps most notably, there is a major disparity in outcomes by geographic region.
Taking A Closer Look
When we examine the summary of pooled effect estimates of mortality and break it down by geographic region, two things jump out right away.
First of all, the strongest inverse relationship between tea consumption and risk of mortality is seen in Asia, with a 16% decrease in all-cause mortality.
But in studies based in Europe, tea drinking is actually not linked to reduced mortality. In fact, the arrow points in the opposite direction! What’s going on here?
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If we glance at the European studies included in the meta-analysis that found increased mortality risk with tea drinking, one thing you’ll see right away is that all of them were conducted in the UK. For example, the Caerphilly Study, which assessed dietary habits of middle-aged Welsh men, showed a significantly greater risk of dying from any cause for those with the highest tea intake.*
Meanwhile, Asian studies which found substantial reductions in mortality linked to tea drinking were mostly performed in Japan. One of these studies, the Shizuoka Elderly Cohort, found that individuals in the highest category of green tea consumption had 55% lower risk of all-cause mortality and 75% lower risk of cardiovascular mortality, compared to people who drank less than one cup per day.
What distinguishes these two groups? One is the type of tea. In the UK cohorts, all of these individuals were drinking black tea, while the Japanese participants were consuming green tea.
Green tea and black tea come from the same plant, but they undergo different processes of manufacturing, which alters their chemical composition in ways that are likely to be physiologically relevant. Although black tea is certainly not unhealthy, it is possible that the polyphenolic compounds that predominate in green tea (catechins, including epigallocatechin-3-gallate or EGCG) are more beneficial than those found in black tea (mainly thearubigin and theaflavin).
Further evidence that this might be the case can be seen in the one study in this meta-analysis which compared mortality outcomes in different tea types. That study found that drinking green tea regularly was linked to a 21% lower risk of all-cause mortality, but frequent black tea consumption had no impact on mortality risk.
Another factor that merits consideration is how tea is consumed in these countries. In the UK, black tea is customarily drunk with milk — in the Caerphilly Study, 99% of tea drinkers reported adding milk to their tea. Why might this be a problem? Well, some experimental research has suggested that protein in milk (casein) can bind to flavonoids in tea, forming complexes that are tough for the digestive system to break down. Since the flavonoids cannot be absorbed, you would expect their ability to neutralize free radicals and combat inflammation to be diminished. However, it is worth noting that research testing this phenomenon have produced conflicting results, with some finding no effect, some finding a relatively minor effect, and even one showing that casein enhanced the antioxidant activity conferred by tea. Clearly more studies are needed to sort this out.
In the meantime, I think the general takeaway here is that tea is broadly healthy to consume, even in large quantities, and you might be best off selecting green tea (probably without dairy to accompany it).
*I would not interpret this study to suggest that black tea is causally related to increased mortality, despite that ominous 2.4 risk ratio. This finding was specific to “men of lower social classes,” and tea drinkers were more likely to be smokers. If anything, including studies like this one probably leads to an underestimate of the average mortality benefit that could be associated with tea drinking.
Random Trivia & Weird News
🐊 About 40 years ago, Key West seceded from the Union and declared war on the United States.
In 1982, the US Border Patrol established a roadblock in front of the roads that connect the Florida Keys to the mainland. Vehicles were stopped and searched, leading to substantial inconvenience for travelers. The city council complained to the federal government that this overreach was a liability to local tourism, but their protests were unheard.
In response, the mayor of Key West, together with the city council, escalated the situation — big time.
They argued that the federal government was treating Key West as a foreign country, and thus they would become one. They declared Key West’s independence from the United States and the city was reborn as the Conch Republic, with the mayor now acting as prime minister of the newly formed micronation. At this time, they also “declared war” on the US, and applied for one billion dollars in foreign aid to cope with the predicament.
Since then, the Conch Republic has continued to celebrate their “Independence Day” every April 23.
Podcasts We Loved This Week
- Alice Lichtenstein: Dietary fat — Evidence vs. misinformation. Via Sigma Nutrition Radio.
- Gloria Mark: Tired? Distracted? Burned out? Listen to this. Via Ezra Klein Show.
Products We Like
MRM Super Foods Matcha Green Tea Powder
Green tea seems to be super healthy. But what is the best form?
Matcha is a powder made from finely grinding green tea leaves. When you ingest it, you are consuming the whole plant, rather than just an infusion like when you brew tea bags. As a result, you wind up getting far more of the bioactive catechins, like EGCG.
This brand in particular is a favorite of ours because it was tested by ConsumerLab for quality, safety, and flavonoid content, so you can be confident in the product. They also offer it in capsules, but the powder is easy to use; you can even add it to juice, smoothies, shakes, etc.
humanOS Catalog Feature of the Week
Daily Performance: Nutrients for Thinking
This week, I’d like to highlight one of the courses from our Daily Performance Program.
In this course, we explore how various aspects of nutrition affect your brain. We look at macronutrients, micronutrients, phytochemicals, as well as the Mediterranean diet pattern and even fasting. We also examine some of the underlying mechanisms, such as changes in blood flow, connectivity, and brain energy.
Check it out if you want to identify some fairly easy ways to improve your daily brain performance.
Wishing you the best,
