People who bottle up their feelings are at least a third more likely to die young than those who regularly express what they're 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.
Another is that the stress of keeping the lid on negative thoughts disrupts the hormone balance in the body, raising the risk of diseases linked with cellular damage, such as heart complaints and cancer.
The researchers stressed that the number of deaths in the study was small and that further investigations are needed.
"These findings reveal significant associations between higher levels of emotional suppression and mortality," they reported.
"The results suggest emotion suppression warrants more detailed investigation as a possible mortality risk."
A previous study suggested that getting angry was good for you because it actually reduced the negative impact of stress.
Scientists at the University of Valencia in Spain found that getting angry increased blood flow to the left frontal region of the brain, which is involved in experiencing positive emotions and also triggers "closeness".
The right side is more related to negative emotions and can provoke withdrawal, fear and sadness.
London-based business psychologist Voula Grand said: "It has long been thought that cancers are partly the result of suppressed emotions.
"Although people learn to hide their feelings at a very early age, they can still be taught to express them later in life. It takes a lot of energy and effort but it can be done."
- DAILY MAIL