Do happier people live longer? An article in the British medical journal Lancet made headlines this month claiming the answer to that question is no. The researchers based their conclusion on data from the Million Women Study in Britain, and it contradicts a large body of research, not to mention conventional wisdom. Because it was a large study, and the Lancet is a well-regarded publication, the message seemed definitive: Happiness doesn't matter for your health.
But the Lancet study is far from definitive. Happiness does matter for your health. A lot. The data the researchers analyzed are indeed interesting and potentially valuable. The Million Women Study surveyed women, ages 50 to 69, on multiple issues and followed them for 10 years. More than 846,000 of the participants answered a question about happiness, and after a decade of follow-up, 4% of them had died. So far, the researchers say the data show that among healthy, first-world women in their 50s, happiness does predict who will die in their 60s, but this effect evaporates once you statistically account for numerous other factors. We believe there are methodological concerns about the study that call this finding into question.
First, the happiness measure used in the Lancet study is weak. In well-crafted research, social scientists think carefully about question and answer design, the ordering of items and how many questions are too many before the participant gives up and stops answering or stops answering honestly.
The Million Women Study asked just one happiness question: How often do you feel happy (from “rarely/never” to “most of the time”). A better approach would have been to ask the question in more ways, with a broader range of positive emotions for participants to choose from.
What's more, the happiness question was the 306th item in a 316-item survey. After answering so many questions about medications, diet and health history, a respondent might be a lot less happy than when she started, and a lot less cooperative. In fact, about 400,000 women in the Million Women Study apparently quit before reaching this question.
If that's not sufficient to show that the approach was flawed, consider this: The study also looked at other psychological factors associated with health, and it showed that none of the ones measured in the same way as happiness — with one question and late in the survey — affected longevity either. One of those factors was stress, yet stress is a noncontroversial, established correlate of nearly all health problems. If the study's stress measure doesn't show a relationship to longevity, the researchers might question whether their measures of other psychological factors, including happiness, are acceptable.
The key to the Lancet study is its statistical analysis of the data. The average participant was 59 when she enrolled in the Million Women Study. The women self-reported their health (from “poor” to “excellent”) at the beginning of the study, and the authors then applied statistics to these data to counter the possibility that the participants' health itself was what was influencing their happiness, rather than vice versa. This makes sense, but it changes the nature of the question being answered. After all, a woman's happiness for the first six decades of her life could have affected her health, yet the analysis essentially took that out of the picture, as though the middle-aged subjects were a blank slate. The authors' question, then, was “Does happiness at 59 predict life span beyond its effects during the first six decades?”
We also have concerns with the authors' choice to statistically control so many other variables. In our work, we hypothesize that the key ways positive feelings influence health are through changes in behaviors. For example, research has shown that positive individuals sleep better, smoke less and exercise more, all of which are known to predict longevity. Thus, when the authors control for all these variables, they are taking away a major path through which happiness is likely to influence longevity. This is like trying to determine whether a hurricane causes damage after controlling for its wind speed. Again, the question is changed, from “Will happy people live longer” to “Will happy people live longer if we take away their healthier behavior?”
Similarly, the authors “held constant” variations in factors such as income, having a romantic partner and religiosity, and yet variations in these factors are likely to be associated with happiness and better health. Controlling for such factors takes away a major part of why happiness is good for us.
Finally, this analysis of the Million Women Study should not be taken out of context. Other studies — some with more objective health measures and longer periods of follow-up — have found robust links between happiness and longevity. Consider the famous Nun Study: Although it had a much smaller sample than the Lancet study, it started when the nuns, all living in similar conditions with similar diets, were 22 and followed them until death. It found that happy nuns survived considerably longer than less happy nuns.
This finding is consistent with dozens of other studies, including laboratory research. Cleverly designed investigations have shown that feeling positive is associated with living longer with HIV, cancer and heart disease, and is even tied to a decreased chance of catching a cold after being exposed to the virus.
So can a million women be wrong?
We believe what the authors of the Lancet study found was not whether happiness is related to longevity but this: Whether a one-item happiness question will predict a shortened life in healthy middle-aged women, if you delete how happiness has affected their health for their first six decades and if you erase the influence of key pathways to health such as social support, smoking and body mass index. Before we judge the true meaning of this research, we plan on waiting to see the effect of happiness once the study is complete, and we have data on many more of the million women (not just 4% of them).
We are happy researchers, and so we plan to be around when that happens.
Ed Diener is a professor of psychology at the University of Virginia and the University of Utah, and senior scientist at the Gallup Organization. Sarah Pressman is an associate professor of psychology and social behavior at UC Irvine. Sonja Lyubomirsky is a professor of psychology at UC Riverside and author of "The How of Happiness."