Coffee: Beneficial or Harmful? What Science Ultimately Says. Coffee is undoubtedly one of the most studied beverages worldwide. For decades, scientists have conducted thousands of studies examining its effect on life expectancy, cardiovascular health, blood sugar levels, and even cancer risk. The truth is that the answer is not simple, but depends on many factors.
The Historical Misunderstanding
For a long time, the scientific community suspected that coffee was harmful. In 1991, the World Health Organization classified it as “possibly” carcinogenic, based on studies linking it to bladder cancer. However, scientists later realized they had confused correlation with causation. People who smoke also tend to drink a lot of coffee, and when studies accounted for smoking, the cancer link essentially disappeared.
The Scientific Evidence in Favor of Coffee
Modern studies present coffee in a completely different light. A large meta-analysis examining decades of research concluded that, for most adults, daily coffee consumption “is more likely to benefit health than to harm it.” People who drink several cups a day have nearly 20% lower odds of dying prematurely compared to those who drink little or none.
Mayo Clinic confirms that coffee can reduce the risk of Parkinson’s disease, type 2 diabetes, and Alzheimer’s disease, as well as metabolic syndrome, chronic kidney disease, liver cancer, cirrhosis, gallstones, and kidney stones. A recent 2025 study found that coffee drinkers have a 40% lower risk of atrial fibrillation recurrence.
How Much Is Safe?
According to the American Heart Association, consuming up to 400 mg of caffeine per day – about 3 to 5 cups of coffee – is generally considered safe for most adults. Moderate consumption has been linked to a lower risk of heart failure, coronary heart disease, stroke, hypertension, and type 2 diabetes. A 2025 study showed that drinking 1-3 cups of black coffee daily is associated with a 14% lower mortality risk.
Risks and Exceptions
Despite the benefits, coffee is not suitable for everyone. Excessive consumption – over 400 mg of caffeine – can cause anxiety, headaches, tachycardia, sleep problems, and worsening of reflux symptoms. Unfiltered coffee (e.g., French press) can slightly increase cholesterol.
Particular caution is required during pregnancy. Pregnant women, those trying to conceive, or breastfeeding should limit caffeine to 200 mg per day – about one cup of coffee. Studies have shown that consuming more than 200 mg of caffeine daily can double the risk of miscarriage.
Personalization Is Key
Perhaps the most important conclusion of modern research is that there is no single answer for everyone. The way each person metabolizes caffeine is largely determined by genetics. The enzyme CYP1A2, responsible for breaking down caffeine in the liver, varies significantly from person to person. “Fast metabolizers” eliminate caffeine rapidly and can enjoy coffee’s benefits without side effects, while “slow metabolizers” retain it in their system for many more hours, resulting in increased risk of hypertension, insomnia, or cardiovascular complications even with moderate consumption. At the same time, age, body weight, stress sensitivity, sleep quality, and the presence of comorbidities (such as gastroesophageal reflux, arrhythmias, or anxiety disorders) critically influence how much coffee someone can tolerate. Within the framework of the Hippocratic approach and modern functional nutrition, coffee consumption should be treated as a personalized decision, based on observing the body’s signals rather than generalized rules. The question, therefore, is not “does coffee do good or harm?” but “does coffee do good for me?”
The Importance of How You Drink It
A crucial point emphasized by experts is that coffee’s benefits can be canceled out by additions. Sugar, flavored creams, and saturated fats turn a healthy beverage into a burdening one. Black coffee or with a little milk without sugar is the best choice.
Temperature also plays a role: consuming very hot beverages has been linked to a tripled risk of esophageal cancer.
Conclusion
The scientific answer is clear: for most healthy adults, coffee – in moderation – is more beneficial than harmful. Moderate consumption (2-4 cups daily) is associated with a lower risk of many chronic diseases and greater life expectancy. However, caffeine tolerance is individualized and depends on genetics, age, metabolism, and each person’s health status. As always, moderation and attention to the body’s signals are the key.
— Dr. Angeliki Makri, Clinical Dietitian, MSc, PhD, Medical School NKUA
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