September 7, 2021

Coffee and your health: How many cups a day is 'just right'?

Daily Briefing

    Around 60% of Americans drink coffee daily—and this habit may protect them against stroke and cardiovascular disease, according to a pre-print study presented at the European Society of Cardiology Congress.

    Cheat sheets: Evidence-based medicine 101

    Study details

    For the study, researchers analyzed data from 468,629 participants in the UK BioBank database. None of the participants had been diagnosed with heart disease when the study began. Participants' average age was 56.2 years old, and 55.8% were women.

    In the study, researchers divided the participants into three groups based on their usual coffee consumption:

    • None, if they did not drink any coffee on a regular basis (22.1%)
    • Light to moderate, if they drank between 0.5 and three cups a day (58.4%)
    • High, if they drank more than three cups a day (19.5%)

    To estimate the association between daily coffee intake and incident outcomes over a median follow-up of 11 years, the researchers used multivariable models. In the analyses, the researchers adjusted for different factors that could potentially influence the association, including age, sex, weight, height, smoking status, high blood pressure, and more.

    In addition, researchers examined the potential underlying mechanisms behind the association between coffee intake and health outcomes. To do this, they used data from 30,650 participants who underwent cardiac MRIs to assess their heart structure and function.

    Key findings

    Overall, the researchers found that light to moderate coffee drinking, or drinking up to three cups a day, was associated with lower risks of stroke and fatal heart disease, as well as death from all causes.

    Specifically, compared to no coffee consumption, light to moderate coffee drinking was associated with a 21% lower risk of stroke, a 17% lower risk of death from cardiovascular disease, and a 12% lower risk of death from all causes.

    And after comparing the cardiac MRIs of participants who did not drink coffee and participants who drank coffee daily, the researchers found that coffee drinkers had "healthier sized and better functioning hearts," which was "consistent with reversing the detrimental effects of aging on the heart."

    Notably, according to Judit Simon, one of the study authors, who works at the Heart and Vascular Center at Semmelweis University, all types of coffee—including caffeinated, decaffeinated, brewed, and instant varieties—appeared to be linked to heart benefits. "In a sub-analysis on types of mostly consumed coffee, decaffeinated coffee was associated with lower risk of all-cause and cardiovascular deaths, but not with lower stroke incidence, suggesting that caffeine is not the main or only component that is responsible for these favorable outcomes," she said.

    According to Simon, instant coffee correlated with a reduced risk of all-cause mortality, while ground coffee was correlated with a lower risk of all-cause and cardiovascular mortality, as well as a reduced incidence of stroke.

    The study adds to prior research

    According to the Harvard T.H. Chan School of Public Health, drinking coffee has been long believed to have health benefits, with low to moderate consumption providing energy, alertness, and increased concentration.

    Previous research has also suggested that drinking moderate amounts of coffee can reduce the risk of certain diseases, such as Type 2 diabetes, liver disease, prostate cancer, and heart disease. For example, one study found that drinking at least one cup of plain, caffeinated coffee a day was associated with a long-term reduction in risk for heart failure.

    But according to the researchers, this new study is the largest to "systematically assess the cardiovascular effects of regular coffee consumption in a population without diagnosed heart disease."

    Simon said, "Our results suggest that regular coffee consumption is safe, as even high daily intake was not associated with adverse cardiovascular outcomes and all-cause mortality after a follow-up of 10 to 15 years."

    Drink coffee plain and in moderation

    Although this study and past research indicate that there are benefits to coffee drinking, some experts caution against consuming too much caffeine. And the concentration of caffeine can vary widely among different caffeinated beverages, making it hard to discern how much is too much. For example, according to the Center for Science in the Public Interest, a grande Starbucks coffee could have 260 to 360 milligrams (mg) depending on the roast, while a large Dunkin' coffee generally has 270 mg of caffeine, USA Today reports.

    According to public health experts at Harvard University and Johns Hopkins University, people should not drink more than an average of 400 milligrams of caffeine a day. As a general rule, USA Today says four to six cups a day may increase health risks.

    In addition, many studies examine only black coffee, so adding creamer, sugar, and other flavors—which also add calories—may undo coffee's health benefits.

    "When it comes to added ingredients such as creamer and sugar, it's best to minimize them, or if you can, skip them altogether and enjoy coffee in its purest form," said Seth Martin, a cardiologist and associate professor at Johns Hopkins Medicine. (Snider, USA Today, 9/2; European Society of Cardiology press release, 8/28; LaMotte, CNN, 8/27; Reinberg, HealthDay/U.S. News & World Report, 8/30)

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