A recent study that was published in the prestigious medical journal The Lancet found that happiness (or unhappiness) does not affect our health and mortality (see The Atlantic or New York Times for coverage about the original piece). According to the NYT, the
“results come from the so-called Million Women Study, which recruited women ages 50 to 69 from 1996 to 2001, and tracked them with questionnaires and official records of deaths and hospital admissions. The questionnaires asked how often the women felt happy, in control, relaxed and stressed, and also instructed them to rate their health and list ailments like high blood pressure, diabetes, asthma, arthritis and depression or anxiety.”
The research article received a huge amount of attention as the results run counter to a large body of extant empirical evidence on the relationship of positive emotions and longevity (please see the paper Happy People Live Longer: Subjective Well-Being Contributes to Health and Longevity for an overview).
Accordingly, a reply to the Lancet article was written as an op-ed in the Los Angeles Times by Positive Psychologists Ed Diener, Sarah D. Pressman, and Sonja Lyubomirsky (Can 1 million women be wrong about happiness and health?). They provide several arguments on why the interpretation of the data about the happiness-health-relationship might be flawed.
For more detail, I urge you to read the L.A. Times article. Just my five cents: The participants were 59 years old on average when entering the study. So, whatever happened before that age was out of scope. Now, I´m not an expert on this – but I hypothesize that how happy you were in your 20s, 30s, 40s, and 50s might (strongly) affect how healthy you are in your 60s and beyond.
For that reason, even though the research is based on a truly large sample, I am not willing to follow the authors´ conclusion.