The damage that anger, depression, anxiety and other negative emotional states can do to heart health is well known. But what about happiness and other positive feelings? Do they offer protection?

A systematic review by researchers at the Harvard School of Public Health (HSPH) suggests that the answer is "yes." But before the less positive among us become depressed about this, take note: there are some qualifiers. It's about what a positive outlook can lead people to do – and not do.

It is not enough to simply not be depressed or angry. What matters is the presence of positive psychological factors.

The researchers found that positive psychological factors do appear to reduce the risk of heart attacks, strokes and other cardiovascular events. It is not enough to simply not be depressed or angry. What matters is the presence of positive psychological factors like optimism, life satisfaction, and happiness.

"[These qualities] are associated with reduced risk of CVD regardless of such factors as a person's age, socioeconomic status, smoking status, or body weight," said lead author Julia Boehm in a press release.

Using data from more than 200 studies published in two scientific databases, Boehm and co-author Laura D. Kubzansky found that the most optimistic people had a roughly 50% reduced risk of experiencing an initial cardiovascular event compared to those where were less optimistic.

Optimism and positive emotions not only offer protection against cardiovascular disease, they also appear to slow the progression of disease.

There is more to this relationship than meets the eye, however. It is not just that happy people live longer; they work at it. The researchers found that people with a sense of well-being tended to engage in healthier behaviors such as exercising, eating a balanced diet, and getting sufficient sleep.

Higher scores on the positive factors were also related to better biological function, such as lower blood pressure, healthier blood fat levels, and normal body weight.

The findings suggest that helping people build their psychological strengths and develop more a more positive outlook could have a real impact on heart health.

The study was published online in Psychological Bulletin on April 17.