People who are too happy die younger than their more downbeat peers, says a new research.
A study which followed children from the 1920s to old age showed that people who were rated "highly cheerful" by teachers at school died younger than their more reserved classmates.
This was because people who were too happy were more likely to suffer from mental disorders such as bipolar, making them less fearful and more likely to take risks that increase the chance of having a fatal accident.
Being too cheerful - especially at inappropriate times - can also rouse anger in others, increasing the risk of a person coming to harm.
Researchers from a variety of universities worldwide also discovered that trying too hard to be happy often ended up leaving people feeling more depressed than before, as putting an effort into improving their mood often left people feeling cheated.
"When you're doing it with the motivation or expectation that these things ought to make you happy, that can lead to disappointment and decreased happiness," the Daily Mail quoted Study co-author Professor June Gruber, from the department of psychology at Yale University in the United States, as saying.
"The strongest predictor of happiness is not money, or external recognition through success or fame. It's having meaningful social relationships," added Gruber.
The study has been published in the journal Perspectives on Psychological Science.