A good friend of mine used to complain all the time about his stress and frustration at work. Every time I saw him, he'd tell me how much "worse" it was -- yet he never did a thing to make his situation better.

Then, one day, things really did take a turn for the worse: He suffered a heart attack.

He was only in his mid 40s.

Luckily, it was a mild heart attack, so it was more of a wake-up call than anything else. But if you let too much stress and negativity get hold of you, you might not get off as easily as my friend did.

Attitude and good stress control are almost as important to heart health as diet and exercise -- and a Harvard analysis of more than 200 studies confirms that an optimistic outlook can cut your risk of a first heart attack in half.

One of the studies even found that happiness can cut your risk of a stroke by 26 percent. And in another, which looked at 300 bypass patients, optimism reduced the risk of a return trip to the hospital or surgery complications by 50 percent over six months.

Naturally, optimistic people were more likely to lead healthier lives in the first place. They ate better, got more exercise, and were even more likely to get the right amount of sleep.

All of these things on their own will lower your risk of heart problems, of course, but the Harvard team wrote in Psychological Bulletin that the benefits of a positive attitude held even after adjusting for all that.

It's not hard to see why, since there's a clear link between the body and the mind.

As my friend found out the hard way, stress can help bring on a heart attack. So it only makes sense that the opposite of stress -- real happiness and positive energy -- can have the opposite effect.

And sure enough, the researchers say the benefits didn't go to people who simply weren't unhappy. They went specifically to people who were happy, satisfied, optimistic, and always hopeful for a positive outcome.

So if you're making changes to make yourself healthy, don't forget to make some of the less obvious changes. Along with a better diet and better habits, give yourself a better attitude, too.