The popular belief that unhappiness and stress can contribute to ill health is unfounded, according to a new study of 1 million women in the UK, which says that happiness and unhappiness themselves have no direct effect on mortality.
While poor health can be a major cause of personal unhappiness, it doesn't work the other way around, say the researchers, despite any associations we often make between how unhappy people are and how long they live.
"Illness makes you unhappy, but unhappiness itself doesn't make you ill," said Bette Liu, one of the researchers, now with the University of New South Wales (UNSW) Medicine in Australia. "We found no direct effect of unhappiness or stress on mortality, even in a ten-year study of a million women."
The researchers sourced their data from the UK Million Women Study. Women were asked to rate their levels of health, happiness, stress, feelings of control, and levels of relaxation.
While the majority of participants indicated that they were happy, one in six said they were generally unhappy. Unhappiness was associated with things like deprivation, being a smoker, lack of exercise, and not living with a partner, but the clearest associations were between women in poor health who tended to say they were unhappy, not in control, and not relaxed.
Over the next 10 years, 30,000 of the women in the study died. After taking into account considerations in the women's lives such as smoking and ill health – including clinical depression and anxiety, which are distinct from general unhappiness – plus lifestyle and socio-economic factors, the researchers found that the death rate among those who were unhappy was the same as the death rate for those who said they were happy.
In other words, unhappiness itself wasn't associated with any statistical evidence of increased mortality, and 1 million women is a pretty massive sample size. The findings are published in The Lancet.
On the surface, the findings appear to clash with another notable study published this week, with researchers at Yale University suggesting that people who hold negative beliefs about ageing are more likely to develop brain changes associated with Alzheimer's disease.
"We believe it is the stress generated by the negative beliefs about ageing that individuals sometimes internalise from society that can result in pathological brain changes," said one of the researchers, Becca Levy. "Although the findings are concerning, it is encouraging to realise that these negative beliefs about ageing can be mitigated and positive beliefs about ageing can be reinforced, so that the adverse impact is not inevitable."
But according to the researchers looking at the data from the UK Million Women Study, any studies that have tied unhappiness levels to reduced mortality haven't correctly allowed for the significant extent to which ill health causes people to feel miserable and stressed.
"Many still believe that stress or unhappiness can directly cause disease, but they are simply confusing cause and effect," said one of the researchers, Richard Peto from the University of Oxford in the UK. "Of course people who are ill tend to be unhappier than those who are well, but the UK Million Women Study shows that happiness and unhappiness do not themselves have any direct effect on death rates."