Keeping a lid on your emotions has long been thought to be bad for mental and physical health.

Now it seems it could actually knock years off your life.

The latest research shows that those who bottle up their feelings are at least a third more likely to die young than people who regularly express what they are thinking.

A study in the US by experts at Harvard School of Public Health and the University of Rochester shows that the risk of premature death from all causes increases by about 35 per cent among those who fail to say how they feel.

But when the researchers looked at specific causes of death they discovered that the risks increased by 47 per cent for heart disease and 70 per cent for cancer.

The findings, published online in the Journal of Psychosomatic Research, suggest that the consequences of bottling up emotions are even more serious than previously thought.

Researchers studied 796 men and women, with an average age of 44, who signed up to a health survey in 1996.

Part of the survey involved questions designed to assess how much the participants suppressed their emotions.

This involved agreeing or disagreeing, on a scale of one to five, with statements such as ‘When I’m angry I let people know’ or ‘I try to be pleasant so that others won’t get upset’.

The survey was repeated 12 years later, during which time 111 subjects had died – mostly from heart disease or cancer.

When researchers analysed the emotion scores, they found that death rates were highest among those most likely to bottle up their anger rather than let people know what they were thinking.

It is not clear exactly how suppressed emotions cause premature death.

One theory is that people turn to alcohol, cigarettes or junk food to help them cope with their hidden feelings.