The constant nagging and bickering of married couples lead to depression and long-term stress, a study reveals.

According to University of Wisconsin, previous research has shown married people are, in general, happier and healthier than singletons.

However, an 11-year study by the University of Wisconsin-Madison questions decades of research linking single life to anxiety and depression.

The researchers assessed a group of married people for depression and gave them questionnaires to rate their stress on a six-point scale.

This process was repeated nine years later.

In the 11^th year, the participants took part in an ‘emotional response test’, measuring how quickly they can recover from a negative experience.

The test, commonly used to assess depression, monitors the corrugator supercilii – or the frowning muscle.

Participants were also shown a mix of 90 positive, negative and neutral photographs and their reactions were recorded.

Those who reported a high level of tension in their marriage were far less responsive to positive images, the study published in the Journal of Psychophysiology concluded.

Professor of Psychology and Psychiatry Richard Davidson said the long-term study shows what makes some people more vulnerable.

“This is extraordinarily important because of the cascade of changes that may be associated,” Prof Davidson said.

“This is the signature of an emotional style that reveals vulnerability to depression,” he said.