Bonn, Germany  - Revenge may be sweet, but it could damage your health and make you unhappier than most other people, according to a study by German and Belgian researchers.

The study conducted among 20,000 people by the universities of Bonn and Maastricht also revealed that people who like to pay back perceived injustices also have fewer friends and are less satisfied with life.

The researchers wanted to find out what influence character traits such as positive and negative acts of reciprocation had on "success" and "satisfaction with life."

People in the poll were asked to what extent they would reciprocate an act of kindness or in contrast pay back an insult.

In summing up the study, Professor Dr Armin Falk from the University of Bonn said that "both positive and negative reciprocation is widespread in the German population."

The study also revealed that positively inclined people were more willing to work longer hours but only if they perceived their wages as being fair.