Could your friends be making you sick? Toxic relationships are linked to cancer, depression and heart disease

It may be wise to keep your friends close and your enemies not quite so close, after all.

Relationships may be as vital to good health as a balanced diet and plenty of rest, new research suggests.

Scientists at UCLA's school of medicine have found that negative social interactions can lead to increased inflammation, which may in turn cause a host of illnesses from cancer to heart disease and high blood pressure.

Call these friends? The stress caused by negative relationships can lead to inflammatory diseases, say scientists

Published this week in the Proceedings of the National Academy of Sciences journal, the study gives solid grounding to the anecdotal evidence that being upbeat and positive - and surrounding one's self with people with that do not represent competitive or toxic relationships - may be one way to avoid getting sick.

Taking a group of 122 healthy young people, the California-based scientists monitored stressful events and compared them to the body's production of two inflammation-causing proteins.

Relying on the age-old method of capturing emotions - the diary - scientists recorded the group's competitive and frictional moments and compared them with the chemicals found in swabs from the inner cheek.

Those who had a negative few days preceding the swab had a higher proportion of the proteins responsible for conditions including high blood pressure, risk of heart disease, cancer and depression, according to Science News.

A similar peak in the pro-inflammatory proteins also occurred after participants were subjected to a stress-inducing numbers quiz and then asked to give a public speech.

The results - which may bring a whole new light to many a bad relationship - are thought to be grounded in evolutionary survival mechanisms.

While the modern link between stress and illness is well-documented, psychologist Nicholas Rohleder from Brandeis University in Waltham, Massachusetts, told Science News that inflammation fends off infections that may once have been the result of fight or flight encounters.

Without the dangers humans once faced when it came to getting through each and every day, stress may lead to unchecked chronic inflammation, he said.