From how many cups does it become unhealthy? It is said that Voltaire drank 50 each day and he lived to a ripe old age.
Coffee is considered good for health to the extent that its benefits outweigh its harmful effects, especially those of caffeine . For example, it has a positive effect against Alzheimer's disease. But that is not proportional to the amount and it should be limited to no more than four cups a day. However, the number depends on several factors ...
About large coffee drinkers who consumed 50 cups a day, I must raise some reservations. This was the case of Voltaire (French philosopher) and he lived up to age 83. He took coffee to relieve the pain he endured, that only during the last years of his life. He would not had lived so long if he had followed such a diet from his young age.
About Balzac, who drank as much and found that it helped to find inspiration, he also found an untimely death at age 51, his heart did not stand up such treatment.
But drinking coffee has very beneficial effects, even if the excitement it causes is not necessarily desirable. We know after several studies on this subject that everyday drinking reduces the risk of Alzheimer's disease.
It is also beneficial against diabetes by reducing the amount of glucose that enters the bloodstream and stimulating insulin production.
As for how much you can drink per day, it depends on many factors.
If you have a fragile heart, or if you suffer from high blood pressure, the recommended amount is zero. If you are suffering anemia too, as it reduces the absorption of iron.
When you are in perfect health, it still depends on the age, size, weight, and especially the type of coffee. It also depends on the habit , because the body becomes accustomed to the caffeine, and it is less effective with time.
A study in 2013 by the Swiss National Science Foundation shows that coffee consumption by children results in a reduction of sleep time which leads to a slowing of brain development. So it must be prohibited before age 16 and be limited to one cup per day before age 18.
It is recommended for an adult to consume no more than 400 milligrams of caffeine per day, for an average weight and size. For pregnant women, it would be 300 mg.
This corresponds to four cups of Arabica coffee, one cup corresponding to a dose on a personal automatic coffee machine. Provided further that you have not absorbed caffeine in other foods (you get cafeine in some drinks).
The robusta coffee contains two times more caffeine than Arabica. So we should be limited to two cups per day over this variety.
Ideally, in addition, one should not drink after 16 hours tp not disturb sleep. Lack of sleep cancel most of the beneficial effects of coffee.
Drinking too much coffee dramatically increases the mortality rate among people under the age of 55, according to a study. This goes up to double for women. By too much coffee, we are talking about more than 20 cups a day. Or 5 large boxes from McDonald.
Reference about age: Nadja Olini, Salomé Kurth and Reto Huber (2013). The Effects of Caffeine on Sleep and Maturational Markers in the Rat.
Even if the experiments are carried out on animals, the findings, said the researchers also apply to humans.