Every day there are new studies linking our mental health to our physical health. Our moods or mental states – positive, neutral, negative – seem to be related to the risk of disease, and indeed, our likelihood of death.

Just last month, for example, a study reported that cardiovascular health is significantly better in people who report being happier. On one level, there is an obvious explanation to the phenomenon: Happy people are more likely to engage in the healthy behaviors – exercise and eating right – that lead to good hearts in the first place. While this relationship may have a lot of explanatory power, the plot seems to be thicker than this.

Are “happy” people set up differently to begin with? For example, their physiologies seem to be different from those of less happy people, with lower levels of the stress hormone cortisol, reduced inflammatory biomarkers, and even changes in the wiring of the brain. All of these differences might make happy people better able to deal with the adverse events that life throws at them, and less likely to feel the effects of stress, which takes a toll on everybody’s health. The happiness-health relationship is at the very least a two-way street.

Psychologists have debated for a while about whether happiness and unhappiness are two sides of the same coin, or whether they’re unique entities.

But what is happiness in the first place? Is it about seeking out activities that make us feel good – indulging a fancy car or going out for a satisfying dinner – or does it have to do with a deeper sense of personal satisfaction over the course of a lifetime?

It’s this question that may be at the heart of the matter. The kind of happiness you experience – and seek – may matter most to your health. In fact, it may be what defines it. There’s a lot we still have to learn about how our heads contribute to bodily health, but here’s what we know about the relationship so far.

Defining Happiness Isn’t So Easy

As most people have probably experienced, there are different types of “happy.” There’s the happiness we get from buying a new iPad and there’s the happiness we get from having a fulfilling job that lets us buy the iPad. This fundamental difference is one that researchers have tried to tease apart, and they’ve described two distinct forms of happiness.

“Hedonic” happiness has to do with pleasure and being satisfied in an immediate sense (“hedonism,” of course, comes from the same root). It’s about how often you feel good, and experience feelings like excitement, interest, and enthusiasm.

People who are higher in eudaimonic, or long-term, happiness have reduced biomarkers of inflammation, like interleukin-6.

“Eudaimonic” well being, on the other hand, has to do with being satisfied with life in a larger sense; it’s about “fulfilling one's potential and having purpose in life,” explains Julia Boehm, who studies the relationship between happiness and health at Harvard. How autonomous or self-sustaining you feel, how interested you are in personal growth, the nature of your relationships with other people, whether you have a deep purpose in life, and your degree of self-acceptance are some of the variables that researchers try to measure to get a good idea of whether a person has eudaimonic happiness.

Some scientists have studied the two forms of happiness in the lab and found some significant differences. Work at the University of Wisconsin has found that people who are higher in eudaimonic happiness have reduced biomarkers of inflammation, like interleukin-6. These biomarkers, according to researcher Carol Ryff, are linked to a number of health problems like metabolic syndrome, diabetes, and cardiovascular disease, so lower levels of them might offer a protective benefit. Ryff has also found that having a strong social support network – an integral part of long term life satisfaction – is connected with lower levels of the same biomarkers.

Eudaimonic happiness (or we could call it personal or inner satisfaction) may even help set up the brain differently. Hedonic or short-term happiness has more to do with the kind of “feel good” behaviors that light up the “reward circuits” of the brain, which rely on the neurotransmitter dopamine. These areas are also important in addictive behaviors, which makes sense, since satisfying an addictive craving is the ultimate form of short term (hedonic) pleasure.

On the other hand, when people who are happy in a deeper way (have more long-term, eudaimonic happiness), are faced with negative stimuli, they have more activity in the prefrontal cortex of the brain, which governs executive planning and higher-level thinking. They also have reduced activity in “lower” brain regions, like the amygdala, the seat of our stress and fear responses. People with eudaimonic happiness are also slower to evaluate negative events as being such, which could mean that they are also less likely to “freak out” over real upsets in life.

Do Definitions Matter? Yes.
Some researchers aren’t so sure that the two concepts need to be separated – and that one good definition of happiness could be sufficient. Boehm says that she prefers the term “positive psychological well-being” over eudaimonic happiness, because, as she says, "It captures a broad range of terms including happiness, purpose in life, optimism, life satisfaction, etc... It can be characterized by the positive feelings, thoughts, and expectations that a person has for his or her life. Essentially, positive psychological well-being is an indicator of psychological functioning that goes beyond the mere absence of disease, e.g., depression, anxiety." (More on this shortly.)

Whether eudaimonic and hedonic are the best labels for happiness is perhaps not so important. But what is clear is that the “feel good” sensations that we tend to think of as happiness may be quite different from what researchers consider happiness – the kind of long-term satisfaction that is shown to be reflected in our mental and physical well-being. If you revise your concept of happiness to include more emphasis on its long-term aspects, you could be on your way to a happier life just from that.

Being Happy Is More than Not Being Depressed

Making the discussion even more interesting (but stickier) is the fact that happiness is more than just not being depressed. As Boehm says, “just because you don't have symptoms of depression or anxiety, that doesn't mean you are functioning optimally.” Psychologists have debated for a while about whether happiness and unhappiness are two sides of the same coin, or whether they’re unique entities. Psychological “ill-being” (depression, anxiety, and anger) has been linked to everything from higher stress hormone cortisol to increased heart risk to increased belly fat to lower “good” HDL cholesterol.

It’s not enough to not be depressed – being happy is what actually gives the physiological benefits that we all want to gain.

But psychological well-being has been linked to different aspects of health, as mentioned earlier, like inflammatory biomarkers and cardiovascular health, though it’s been studied less. One study directly compared the biological changes associated with well-being and ill-being, and found enough differences to suggest that well-being and ill-being are not likely two sides of the same coin, but that they are fundamentally different entities. This may explain why it’s not enough to not be depressed – being happy is what actually gives the physiological benefits that we all want to gain.

What Makes You Happy?

If you’re not the happiest person in the world, don’t panic. There are ways to increase your satisfaction in life and develop a stronger sense of the kind of well-being that could serve you well mentally and physically, now and in the future. Spending some time thinking about the kinds of things that give you pleasure might be the first step.

A couple of years ago, a team of researchers reported that the types of “American Dream”-type goals we often think of as being the ultimate happiness-inducers aren’t so happiness-inducing at all.

By getting in touch with your values and finding ways to give back, you might, unwittingly, be serving yourself. Doing things that just make you feel good won’t cut it.

People whose goals involved personal growth and the community were much happier than people who sought money or fame. This sounds a lot like the hedonic/ eudaimonic divide. “By attaining the ‘American Dream goals,' [big house, fancy car, designer clothes]” said the study's author Edward Deci, “you are actually feeling less satisfied in the need for autonomy and feeling effective in the world [because you are dependent on external measures outside your direct control], and that leads to more ill−being.”

So it seems like going after the material goods that are so appealing – a nice house, car, or bottle of wine – may actually make us more psychologically impoverished than the “larger” goals, like personal growth and self-satisfaction.

This study underlines the divide between what we may think makes us happy and what actually makes us happy – and, by extension, healthy. By getting in touch with your values and finding ways to give back, you might, unwittingly, be serving yourself. Doing things that just make you feel good won’t cut it. “If you are living a full life,” says Deci, “you will experience a lot of positive affect [emotions]. If you want to know something about living a meaningful life, just looking at subjective well-being is not enough.” In other words, finding activities that have intrinsic value, and being a part of them – by doing work you believe in, volunteering, or helping out your community in other ways – is probably much more beneficial.

Choosing the Sunnier Path

In the end, the relationship between happiness and health is not simple, and there’s a lot we don’t know. It’s beyond the scope of this article, but we’re also learning that happiness, or more specifically, having a sense of purpose in life, is linked not only to physical health, but also to brain health.

For example, Alzheimer’s patients who have a sense of purpose in life have fewer symptoms (cognitive deficits) than people who have less purpose. On the flip side, people who are depressed in their middle or old age are at higher risk of developing certain forms of dementia, including Alzheimer’s. These relationships also complicate our understanding of happiness and health, and are worth keeping in the back of our minds.

The bottom line is that we know that there are strong relationships between health and happiness, life satisfaction, and purpose, but how it works is still being mapped out. Mental well-being, ill-being, social support, lifestyle choices, and physical health all make up a vast matrix of variables that influence and play off one another.

While researchers are still working on pulling apart these relationships, taking some time to get in touch with your purpose will likely benefit your health, not to mention make your day-to-day life more pleasant in the process. The coming years are likely to bring a much deeper understanding of what happiness actually is, psychologically and physiologically speaking, and this may itself result in a deeper understanding of what health actually is.