We've arrived at a point in human history where our health is assaulted like never before. The phthalates that soften our shower curtains and the bisphenols that shatterproof our water bottles are endocrine disruptors that, research is now showing, may lead to lower testosterone in boys and girls who can look forward to breast cancer.
It seems as though you have to be filthy rich or join a commune to eat decent food these days; the choice of a new generation is between aspartame and high fructose corn syrup. The pills we take to quit smoking make us consider plunging from high roof tops instead. And these are just the plagues of the developing world.
It's little wonder, then, that our hearts would soar at each study that makes the news cycle by suggesting happiness can make us physically healthier. So far, research has shown that happy people may suffer fewer strokes, colds and respiratory illnesses. Happiness has been associated with faster recovery from minor illnesses and surgeries. And the holy grail of health, longevity, has been linked to it as well.
This is, of course, good news. Even taking into account the unforeseeable and unavoidable threats to our happiness that constitute the crushing stress of life in the 21st century, we humans are surprisingly capable of maintaining a sunny outlook. We can shrug off a bad mood; try shrugging off an endocrine disruptor.
We appear to have gotten ahead of ourselves, however. The truth is, we have no idea if happiness leads to good health.
The mantra that provides the basis for scientific inquiry is correlation does not imply causation. While we may show A and B are linked, this does not mean that A causes B. Thus far, science has been able to come up with correlative evidence that suggests a link between happiness and good health. The causation that demonstrates that link has so far remained elusive.
Take serotonin, for example. Studies that have shown that depressed people tend to have low levels of serotonin, a mood-regulating hormone, and higher body mass indexes, a health risk. So is serotonin, a mood-regulating hormone, the link between happiness and health, or is it that depressed people tend to eat more comfort food? Happiness and health may be accompanying byproducts of a third factor, like strong social networks or good dietary decisions. You can see how this gets frustrating.
A couple of researchers in the field -- Carnegie Mellon psychologist Sheldon Cohen and Yerkes Primate Research Center Psychobiology director Mark Wilson -- talked to me about why science remains confounded by the unseen tie that binds happiness and health. For one, happiness is a devil to define. Parts per million, micrograms, watts per square meter, light years -- these are like warm blankets of sense to scientists, who require quantification for their inquiry. It's incredibly difficult to measure 10cc of happiness, and if we could, we'd all be shooting it up and really wouldn't care whether it made us healthier at all.
"The central question is what is happiness," Dr. Wilson told me in an e-mail. "Is it solely a cognitive state that can only be measured by asking someone how he or she feels or is it a behavioral phenotype that can be measured by an individual's propensity to interact with others? I am not sure."
Researchers have narrowed the field a bit in defining the happiness they require to study. They've come to focus on trait affect, our neutral baseline levels of happiness, over state affect, how we react to unforeseen events like winning the lottery or having a leg amputated.
But this presents even more challenges. Measuring state happiness would be much easier; researchers could simply take away a kid's toys for a few weeks and watch for signs of susceptibility to the flu, for example.
Researchers must alter the happiness that describes an individual's overall personality to carry out a proper study, Dr. Cohen says. "In order to prove causation, we will need to be able to manipulate levels of happiness," he told me. "Can we make people happier? It of course is a difficult task to change such a stable disposition."
Such questions (and indeed, the pursuit of the study of happiness itself) may appear wholly academic. If happiness does lead to good health, then our (lack of) awareness of how it functions shouldn't alter the dynamic. Who cares, in other words? But while most of us are content with correlation, courts and policymakers still generally require proof to act. A class action lawsuit to halt bisphenol production will generally require proof that it's harmful. Legislation that creates expensive programs focused on creating a happier population will generally require proof it's beneficial to health. And the proof these things require will generally require causation.
Josh Clark is a senior writer for the Web site HowStuffWorks.com and host of the podcast Stuff You Should Know. He and his co-host Chuck Bryant are working on the Stuff You Should Know Super Stuffed Guide to Happiness, an audiobook due out this April in iTunes