The bitter truth: 25 cups of coffee a day might not be healthy
July 24, 2019
News coverage of a 2019 study on coffee consumption has cardiologists on edge. The headlines read like a coffee lover’s dream: “Up to 25 cups of coffee a day safe for heart health!”
While that may be a clever way to capture social media clicks and TV sound bites, it’s not what the actual data tell us – and it’s not a habit patients should assume is safe.
Researchers from Queen Mary University conducted the study with more than 8,000 people in the U.K., causing a stir due to the large sample size and its supposed findings, which contradict several previous studies on how much coffee is safe to drink. Pair these factors with improper reporting, and we're faced with a “telephone game” of inaccurate assumptions about coffee consumption.
Before you reach for your fifth (or 25th!) cup, check out these heart-health details espresso enthusiasts should consider.
Real details from the study
The study actually excluded people who drank more than 25 cups of coffee a day.
This is explicitly stated by Queen Mary University researchers who set three categories for participants’ coffee consumption:
- Less than one cup a day
- One to three cups
- More than three cups a day (the average among this group was five cups a day)
Then, researchers compared data from the “less than one cup” participants to the other two groups, clearly excluding outliers. Next, they overlaid their findings on heart imaging data for these patients.
Using this method, researchers found no difference in arterial stiffness (a heart attack and stroke risk factor) amongst participants, regardless of whether they drank more or less than three cups of coffee a day.
“In the U.S., heart disease is the No. 1 killer of men and women. And coffee is the most popular beverage in the U.S., according to 2017 data from MarketWatch. Such a potentially dangerous crossover warrants a thorough randomized trial rather than an observational study.”
However, this conclusion is questionable because:
- These data were correlated findings, not direct cause and effect implications on participants’ heart health.
- Coffee-drinking data were self-reported, and therefore potentially skewed.
- Groups were not assigned to drinking a certain amount daily. A person might drink no coffee one day and five cups the next, which could affect outcomes.
In the U.S. – indeed, the entire world – heart disease is the No. 1 killer of men and women. And coffee is the most popular beverage in the U.S., according to 2017 data from MarketWatch. Such a potentially dangerous crossover warrants a thorough randomized trial rather than an observational study.
It’s unreasonable to drink that much coffee.
Until I read this paper, I didn’t realize there was a population of people who actually drink more than 20 cups of coffee a day. How can they get anything done between buying or making coffee and running to the restroom all day?
This also brews up an important socioeconomic consideration. People who can afford to drink excessive amounts of coffee are likely to have adequate access to health care, nutritious food, and a safe place to exercise. All these factors affect a person’s heart health, though these details were not addressed in the paper out of Queen Mary University.
This same conundrum has arisen in many heart-health conversations, perhaps most notably in the discussion of whether beer or red wine consumption is “healthier.” Hypotheses often are drawn from European studies of heart health without looking at the overall lifestyle picture compared to the U.S. And while moderate red wine intake has been shown not to negatively affect heart health, high-end wine costs more than the average beer, resulting in socioeconomically skewed data.
The study didn’t address notable symptoms besides arterial stiffness.
Everyone processes caffeine differently, and when we’ve had too much, many people experience side effects such as headaches, sleeplessness, digestive issues, and blood pressure spikes. Personally, I can’t drink more than three cups of coffee a day without getting heartburn and a stomachache.
Also, there’s no description of the type of coffee patients report drinking. Are they having decaf, regular, or high-caffeine varieties? This is important to make an apple-to-apples comparison. Are they having black coffee, or gourmet concoctions loaded with sugar? Long-term excess sugar consumption can contribute to Type 2 diabetes, which is a major heart disease risk factor.
So, how much caffeine is safe?
Most doctors recommend capping daily caffeine intake at 400 mg, which is equivalent to about four cups of coffee. This is because studies of energy drinks suggest that drinking caffeine can cause acute spikes in blood pressure and arterial stiffness and can result in emergency room visits and even deaths. In 2018, the U.S. Food and Drug Administration issued a warning that exceeding 1,200mg of caffeine a day can cause potentially toxic side effects, including heart arrhythmia, elevated heart rate, or seizures.
If a person already has high blood pressure issues, they’re at increased risk for adverse effects. This is particularly worrisome because high blood pressure often doesn’t cause noticeable symptoms, and many people who have it don’t know that they do.
Patients often ask me whether they drink too much coffee. Like most things in life, moderation is key. If they are limiting themselves to three or four cups a day (or less), and generally avoiding beverages loaded with sugar, they probably don’t need to quit drinking coffee. Studies suggest that patients with high blood pressure might not notice a change in their readings if they stop drinking coffee altogether.
To answer these questions definitively, we need a randomized study in which participants are assigned to drink specific amounts of coffee with standardized measurements of caffeine and sugar. Further, we also need to consider participants’ socioeconomic and health histories in these large-scale studies to glean more informative data.
That said, I’ve never seen a study in which participants were required to drink more than three or four cups of coffee a day. That might be tough for some participants, let alone difficult for researchers to enforce outside a clinical setting.
The biggest thing patients should take away from this story is that explosive headlines like “You can drink 25 cups of coffee a day!” should be taken with a grain of salt. Don’t go on a coffee bender just because a few news stories suggest you can. Talk to your doctor and make a healthy, informed decision. Your heart will thank you!
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