Scientists have long known that Type A personalities and people who are chronically angry, anxious or depressed have a higher risk of heart attacks.

Now a Harvard review of the flip side of that psychology concludes that being upbeat and optimistic just may help protect against heart disease.

Rather than focusing only on how to lessen heart risks, "it might also be useful to focus on how we might bolster the positive side of things," said lead researcher Julia Boehm of the Harvard School of Public Health.

Boehm reviewed dozens of studies examining a positive outlook - as determined by various psychological measurements - on heart health. Optimism in particular seems key, as a number of studies found the most optimistic people had half the risk of a first heart attack when compared to the least optimistic, Boehm said.

Why? Previous work shows the stress associated with negative psychological traits can lead to damage of arteries and the heart itself.

Boehm found that people with a better sense of well-being tend to have healthier blood pressure, cholesterol and weight, and are more likely to exercise, eat healthier, get enough sleep and avoid smoking. But she cautioned that it will take more research to tease apart if a positive outlook makes people feel more like taking heart-healthy steps - or whether living healthier helps you feel more positive. 

What if you're by nature a pessimist? "That's a hard question. There's no magic happy pill," Jackson said.

Some research has found that asking people to smile helps put them in a better mood, Boehm noted, although long-term effects aren't clear.

"Sometimes it's hard, particularly in tough economic times, but taking a moment to just relax and enjoy a sunny day might be good heart health," Jackson said.