"Happiness doesn't make you live longer, survey finds," reports The Guardian after a survey of more than 700,000 women found no evidence of a direct cause and effect link between happiness and life expectancy.
There has been speculation that happiness in itself – rather than factors that can stimulate happiness, such as good health – may prolong life.
This could possibly occur through some type of biological changes in immune or metabolic function, which could boost health. Stress and unhappiness could have a similar negative impact.
The women were asked to rate their health and happiness by questionnaire, and death from any cause was examined about 10 years later. Unsurprisingly, the researchers found poor health was linked to unhappiness.
After allowing for this and other associated factors, the researchers found (un)happiness does not appear to have any effect on risk of death.
A note of caution, however: the researchers used a large sample, but from a very specific population of middle-aged women in the UK. This means further research should be conducted in a wider sample of men and women from a range of countries to see if the findings are replicated.
Most people want to have a good quality of life as well as a long one. Read more about how to feel happier.
The study was carried out by researchers from the University of Oxford and the University of New South Wales, and was funded by the UK Medical Research Council and Cancer Research UK.
This study has been reported accurately in a number of media sources, with useful quotes from the study's researchers.
The Mail Online quotes a professional from University College London who said the research uses a very specific population, so we do not know how the findings will translate for other groups.
They go on to say there is a lot of evidence that had opposite findings, so we need to see these findings replicated before opinion is changed on the link.
This was a large population-based prospective cohort study of more than 1 million women (hence its name, "The Million Women study") in the UK aged 50 and over.
The cohort itself was drawn together by researchers who aimed to investigate the effect of various reproductive and lifestyle factors on women's health.
This particular study looked at whether self-rated happiness has a direct effect on mortality, after taking into account other health and lifestyle factors that may have had an influence on both wellbeing and mortality risk.
This type of study is good for assessing links between exposures and health outcomes. It can provide some evidence of a possible link (or lack of one), but it still cannot conclusively prove cause and effect.
The Million Women study invited women to join between 1996 and 2001. Recruitment took place at a number of breast cancer screening centres.
Women received a questionnaire along with their invitation for screening and were asked to return the completed questionnaire at the screening appointment.
The questionnaire contained questions on the following:
Every three to five years after recruitment, women were sent a repeat questionnaire assessing the same information.
To establish the women's level of happiness, three years after recruitment (baseline) they were asked, "How often do you feel happy?", with possible responses being "most of the time", "usually", "sometimes", or "rarely/never".
They were also asked how often they felt in control, relaxed and stressed. Women were also asked about their current health status, which they rated as "excellent", "good", "fair", or "poor".
Data from the questionnaire was used to investigate associations between happiness and deaths occurring up to January 2012.
When analysing data, mortality analyses excluded women with a history of illnesses such as heart disease, stroke, lung disease, or cancer, and analysed links for these conditions separately. The main reason for this was to reduce the risk of reverse causality, where people who are ill do not feel happy.
At the start of the study, 845,440 women with an average (median) age of 59 years responded to the question about happiness. This found 39% were happy most of the time, 44% usually happy, and 17% unhappy (16% sometimes happy and 1% rarely or never happy).
Analyses on the link between happiness and risk of death was limited to the 719,671 women without cancer, heart disease, stroke, or chronic obstructive airways disease at baseline.
The strongest sociodemographic and lifestyle factors associated with being generally happy were:
The strongest associations with unhappiness were:
Women were followed for an average of 9.6 years after completing the baseline questionnaire. A total of 48,314 deaths were reported during this time.
When adjusted for the effect of age, women reported as unhappy had a 34% increased risk of death compared with happy women (rate ratios [RR] 1.36, 95% confidence interval [CI] 1.33 to 1.40).
The researchers then adjusted for the possible confounding effect of a number of other variables: self-rated health, treatment for high blood pressure, diabetes, asthma, arthritis, depression or anxiety, and several sociodemographic and lifestyle factors, including smoking, deprivation and body mass index.
They then found unhappiness was no longer associated with death from any causes (RR 0.98, 95% CI 0.94 to 1.01) or specific causes of heart disease (RR 0.97, 0.87 to 1.10) or cancer (RR 0.98, 0.93 to 1.02). Findings were similar for related measures such as stress or lack of control.
The researchers concluded: "In middle-aged women, poor health can cause unhappiness. After allowing for this association and adjusting for potential confounders, happiness and related measures of wellbeing do not appear to have any direct effect on mortality."
This large prospective study aimed to assess whether happiness or related measures of wellbeing are associated with risk of death, after allowing for the influence of the poor health and lifestyles of people who are unhappy.
The study found poor health was linked with unhappiness in middle-aged women. However, after allowing for this association and adjusting for the influence of other factors that may be associated, such as smoking and poor socioeconomic status, happiness and related measures of wellbeing do not appear to have any direct effect on death.
This suggests that, as has sometimes previously been speculated, (un)happiness does not have a direct influence on mortality, but is being influenced by other associated factors.
However, this study has both strengths and limitations. The strengths include the fact the study population is very large and the women included have been followed for a long period of time using electronic linkage to their NHS records.
The researchers did make an effort to limit the effects of potential confounders and reverse causality in their analyses, which strengthens their results.
However, there are limitations: the study recruited only UK-based middle-aged women, so we do not know if the findings would be applicable to men or other populations.
The self-reported nature of the questionnaire may also introduce bias, particularly as happiness and wellbeing are subjective measures, so what could be a "similar" feeling may be rated completed differently by two different people, depending on their usual disposition.
Also, as the women were recruited through the National Breast Cancer Screening Programme, this will have excluded women who do not attend or may have different health, lifestyles and feelings from those who choose to attend screening.
The study findings are of undoubted interest to this debate, but because of its limitations, we should be cautious before dismissing the idea that stress and unhappiness may be linked to risk of death. Further research should be conducted in a wider sample of men and women from a range of countries.
While happiness in itself may not contribute to an increased lifespan, many of the factors that promote wellbeing and happiness do, such as good health, not smoking and connecting with others. Read more about how you can improve wellbeing in your life.