“Experiences that induce positive emotion cause negative emotion to dissipate rapidly. The strengths and virtues…function to buffer against misfortune and against the psychological disorders, and they may be the key to building resilience. The best therapists do not merely heal damage; they help people identify and build their strengths and their virtues,” wrote Martin Seligman, former president of the American Psychological Association and the father of the field of positive psychology, in his book Authentic Happiness. And solid research continues to accumulate supporting this view. Here are a few important studies on happiness and health.

Happiness and Longevity

A landmark study involving nuns was able to pinpoint health benefits that come with positive emotion. (Nun studies work well because so many other lifestyle variables are uniform, so reported differences can often be narrowed down to a handful of factors, like personality and outlook.) In studying the lives and deaths of the nuns, given clues to their emotional state, researchers were able to make an important discovery about happiness and health-positive emotion is correlated with longevity. Ninety percent of the most cheerful quarter of nuns was alive at the age of eighty-five, whereas only 34% of the least cheerful quarter lived to that age. Similarly, 54% of the most cheerful fourth was alive at age ninety-four, versus 11% of the least cheerful.

Happiness and Marriage

As if that’s not enough, positive emotion is also linked by research to marital satisfaction. In another astonishing study, researchers were able to examine the cheerfulness of smiles in women’s yearbook photos and predict which ones, on average, would be more likely married, stay married, and experience more personal well-being over the next thirty years. (Hint: it was, again, the most cheerful group.) This is a great way that couples can keep each other healthy.

Happiness and Optimism

Researchers have also found optimists to have longer lives. Optimism is distinct from positive emotion, though the two are related. Rather than just being cheerful, however, optimists tend to see the world in a distinct way: when positive events occur in their lives, they give themselves personal credit, attribute the cause to lasting traits under their control, and see each good event as a sign that more positive events are to come. This specific lens through which they see the world allows them to maintain more of an internal locus of control (a sense of personal control over things), as well as resulting health-promoting behaviors and is associated with many benefits, including longevity. One study found that optimists had a 15% longer lifespan on average. Clearly, happiness and health can be linked by optimism.

Happiness and ‘Mature Defenses’

Another factor that’s closely related to positive emotion and optimism is a set of strengths known as ‘mature defenses’. These traits, which are not displayed by everyone, and vary over a lifespan, including altruism, the ability to delay gratification, future-mindedness, and humor.

Happiness and Health

Happiness researcher Robert Holden conducted a survey and found that 65 out of 100 people would choose happiness over health, but that both were highly valued. Fortunately, we don’t have to choose: happiness and health go hand-in-hand. As Holden stated, “[T]here is no true health without happiness”. There is also ample evidence that unhappiness—depression, anxiety, and stress, for example—are also linked to poorer health outcomes. These negative states, if chronic, can dampen immunity and increase inflammation in the body leading to a multitude of diseases and conditions. The principles of positive psychology can combat these negative states, further increasing the likelihood of health.