Coffee - harmful or healthy?

Effect of Coffee on Health

Sometimes coffee is demonised, then caffeine is said to be very healthy again. As a neurobiologist and author who drinks "litres" of coffee every day, I am constantly asked the question: "What is true? Is coffee or caffeine now harmful or healthy?" In fact, a whole series of scientific studies were published on this question and summarised in the renowned New England Journal of Medicine in July 2020. Conclusion: 3 to 5 standard cups (235 ml) of coffee (which corresponds to 270-450 mg of caffeine) are healthy, they have a positive effect on the brain, and consistently reduce the risk of various types of cancer and chronic diseases.

Not all coffee is the same

But you have to bear in mind: Not all coffee is the same; it depends, for example, on how it is prepared. And what applies to coffee does not necessarily apply to caffeine or vice versa. Some of the observed effects were observed with coffee, but not with synthetic caffeine, such as that contained in soft and energy drinks. And some effects are detectable both with coffee, whether it contains caffeine or is decaffeinated. This all suggests that there are other substances in coffee besides caffeine that have a health effect. Let's take a look at the most important proven effects of coffee in detail:

1. coffee is not carcinogenic

The results of many and extensive studies show that coffee consumption is not associated with an increased risk of cancer . On the contrary, coffee even seems to protect against some types of cancer, for example skin, breast and prostate cancer, and more strongly against uterine and liver cell cancer. Coffee also appears to be healthy for the liver as a whole: coffee consumption is associated with a lower risk of developing liver cirrhosis and fibrosis.

2. coffee does not raise blood pressure - caffeine does

Studies have shown that coffee does not cause a rise in blood pressure even in people with high blood pressure. However, this only applies to coffee, not to other caffeinated drinks! Synthetic caffeine, such as that found in soft or energy drinks, appears to raise blood pressure. Presumably, other natural substances in coffee counteract the blood pressure-increasing effect of caffeine.

3. caffeine is bad for diabetes - coffee is not

Similar to blood pressure, coffee and synthetic caffeine have different effects on diabetes. While synthetic caffeine reduces the effect of insulin, at least for a short time (and thus increases the blood sugar level), the consumption of coffee, on the other hand, has no effect on insulin. According to some studies, regular coffee drinking is even associated with a low risk of type 2 diabetes . So here, too, other ingredients in the coffee bean seem to have a positive effect on diabetes.

4. coffee is good for the heart

Even 6 cups of coffee per day are safe for the heart - even in patients with heart disease. On the contrary, the consumption of 3 to 5 cups of coffee even seems to reduce the risk of cardiovascular disease. The question of whether coffee can increase (bad) LDL cholesterol seems to depend on how it is brewed: Unfiltered coffee (French Press, Turkish or Scandinavian style), consumed in high quantities, could be problematic for cholesterol levels.

5. stay awake with caffeine?

Caffeine has a positive effect on performance for a short time, it reduces tiredness and increases alertness. However, caffeine cannot compensate for the drop in performance after a prolonged sleep deficit. In addition, coffee drunk later in the day can have a negative effect on the quality of sleep, whereby the effect of caffeine on sleep varies greatly from person to person.

6. coffee does not dehydrate

High caffeine consumption can indeed stimulate urine excretion. However, studies could not find any negative effects on the water balance , even when moderate doses (≤ 400 mg/day) were consumed over a longer period of time.

7. caffeine is still not harmless

With caffeine, too, the dose makes the poison. In a very high dose, caffeine can cause anxiety, restlessness, nervousness, insomnia, agitation and psychomotor agitation. However, these side effects are only to be expected at doses of 1.2 g or higher. Caffeine can be lethal from a dose of 10 to 14 g; however, this would require drinking 75 to 100 cups of coffee in a short period of time.

More dangerous are modern caffeine drinks such as energy drinks or shots, especially when mixed with alcohol. Cardiovascular, psychological and neurological problems, even deaths, have been reported. Of all people, children and adolescents - among whom these drinks are very popular - seem to be particularly susceptible to the side effects of high caffeine doses.

How much coffee is healthy?

Scientists recommend limits of 400 mg of caffeine per day for adults, and 200 mg per day for pregnant and breastfeeding women. However, as mentioned above, the caffeine in coffee can sometimes show different effects than the free caffeine in synthetic drinks. In the table you will find the caffeine content of various drinks (per 100 ml):

Caffeine content per 100 ml:

  • Espresso 135 mg
  • Filter coffee 55 mg
  • Instant coffee 40 mg
  • Energy drinks (Red Bull or similar) 32 mg
  • Fritz-Cola 25 mg
  • Black/green tea 20 mg
  • Coca Cola 10 mg

400 mg of caffeine is equivalent to: 300 ml of espresso, 730 ml of coffee, 2 l of tea or 4 l of Coca Cola


Concluded the authors: "Current scientific evidence does not justify recommending caffeine or coffee consumption for disease prevention, but suggests that moderate coffee or tea consumption can be part of a healthy lifestyle in adults who are not pregnant or breastfeeding and have no specific health problems."


Rob M. van Dam, Frank B. Hu, Walter C. Willett. Coffee, caffeine, and health. N Engl J Med. 2020; 383:369-378. DOI: 10.1056/NEJMra1816604