A groundbreaking new study revealed today that happiness may be a cause for depression.

Studies show that there is a darker side to feeling good and that the pursuit of happiness can sometimes make you . . . depressed. Too much happiness will make you gullible, selfish, less successful and, in some cases, suicidal.

Happiness does have benefits. It can protect us from stroke and the common cold, makes us more resistant to pain and even prolongs our lives. Yet, June Gruber, a professor of psychology at Yale University who has studied happiness, warns that it’s important to experience positive moods in moderation.

She compares happiness to food: Although necessary and beneficial, too much food can cause problems; likewise, happiness can lead to bad outcomes. “Research indicates that very high levels of positive feelings predict risk-taking behaviors, excess alcohol and drug consumption, binge eating, and may lead us to neglect threats,” she says.

“You don’t want to eat too much cake or broccoli or meat. Too much is bad. Less is more. And that goes for happiness, too.”

How else can excessive joy, or having lots of positive emotions and a relative absence of negative ones, hurt you?

First, it may hamper your career prospects. Psychologist Edward Diener, renowned for his happiness research, and his colleagues analyzed a variety of studies, including data from more than 16,000 people around the world, and discovered that those who early in their lives reported the highest life satisfaction (for example, judging it at 5 on a 5-point scale) years later reported lower-income than those who felt slightly less merry when young. What’s more, they dropped out of school earlier.

Psychologists point out that emotions are adaptive: They make us change behavior to help us survive. Anger prepares us to fight; fear helps us flee. But what about sadness? Studies show that when we are sad, we think in a more systematic manner. Sad people are attentive to details and externally oriented, while happy people tend to make snap judgments that may reflect racial or sex stereotyping.

In a 2005 study in the Journal of Personality and Happiness, University of Chicago psychologist Gwen Bolden asked 94 student to “get happy”… “really happy.” The students did everything they could possible do to make themselves happy – including sex, drugs and rock n’ roll – but soon after, the students were “depressed.”

“See happiness needs to be controlled. Too much will make you depressed and cause you to stay in bed and watch reality TV all day. Better to be a little happy or even a little sad. Too much happiness is no good.”