According to Lucie Nusbaum from Germany's Association of Nutritionists, once this breaking point has been reached, further cups of coffee no longer lead to improved concentration or performance.
Instead contrary occurs, which is the clearest difference between coffee consumption and suffering from an addiction. Alcoholics, for example, experience the desired effects from alcohol with every extra drop.
The so-called coffee addiction is no more than a habit, according to the nutrition expert. Despite this reality, many people suffer from withdrawal headaches if they don't get the required amount of coffee in a day. Coffee gives a short-term boost to the body's blood pressure and when this boost fails to arrive then this can affect the brain.
If a person wants to give up coffee due to a sensitive stomach, they will have to wait until feeling fully normal again. "I have to live with the withdrawal headaches, which can last a couple of days," explains Nusbaum, who doesn't want to give up drinking coffee entirely.
"It's an effective way for people with low blood pressure to get up and running in the day," she says.
A cup in the morning can give a boost that lasts the whole day although the effects only last between 10 and 30 minutes for people with normal blood pressure.
"The general rule is that coffee works quickly, for a short length of time and the effects wear off," concludes Nusbaum.
(Sapa July 2011)