"Optimists are more likely to live longer than those who have a more negative approach to life, a US study has found," BBC News reports. The Mail Online reports on the same study claiming that "Optimists are up to 70% more likely to live to be 85".
The study used information collected from male war veterans and female nurses taking part in 2 long-running studies in the US. The participants were around 60 to 70 years old when they completed optimism questionnaires, and the researchers looked at whether optimism was linked to living longer.
People who had the highest optimism scores had a lifespan about 9% longer than those with the lowest scores. But despite media reports, the most optimistic were in fact no more likely to live to age 85. The 70% figure came from a result that had not taken account of all influencing factors.
Ultimately this research cannot prove cause and effect. Both optimism and lifespan may be influenced by many hereditary, health, lifestyle and personal factors. People with a good overall standard of health and wellbeing are probably more likely to be optimistic about their future. While researchers attempted to adjust their analysis for these sort of factors, it's hard to remove their influence fully.
It's also questionable how applicable the results of these optimism assessments, taken 15 to 30 years ago from very specific groups of older US nurses and war veterans, are to the general UK population.
Nevertheless the research highlights the importance that mental health and wellbeing can have on physical health.
The study was carried out by researchers from the National Center for Posttraumatic Stress Disorder of the Veterans Affairs Boston Healthcare System, Boston University School of Medicine, Harvard Medical School and other institutions in Boston, US.
It was funded by the National Institutes of Health, Clinical Science Research and Development Service, US Department of Veterans Affairs, and Fonds de Recherche en Santé–Quebec. It was published in the peer-reviewed journal, PNAS.
The UK media coverage was generally positive in tone taking the findings at face value without considering the many limitations of this research. Notably many of the media sources highlighted the claim that optimists are 70% more likely to live to 85, which is not correct.
Arguably the authors of the study are partly to blame for this, as they placed the headline-grabbing result, which did not adjust for all confounding factors, into the abstract.
The researchers used data collected from 2 long-running US cohort studies. They looked at women participating in the Nurses' Health Study, and men participating in the Veterans Affairs Normative Aging Study, to see whether assessments of optimism were linked with lifespan.
Prospective cohorts can look at links between a risk factor or exposure and later health outcomes.
However, the data cannot prove direct cause and effect between the 2, particularly considering the 2 cohorts were not set up to examine this question. Many factors may influence both optimism and lifespan.
The Nurses' Health Study recruited female nurses in 1976 and has since followed them with health and lifestyle questionnaires every 2 years. The participants completed an optimism assessment in 2004 (when they were on average 70 years old), and their survival was tracked until 2014.
The Veterans Affairs Normative Aging Study recruited male veterans in 1961, who completed an optimism assessment in 1986 (average age 62) and had their survival tracked to 2016.
The researchers say that optimism can be defined either as a disposition (where people have a general tendency to be optimistic), or based on attributions (where people are optimistic because things have generally gone right for them in the past).
The Nurses' Study assessed dispositional optimism, said to "refer to the relatively stable, generalised expectation that positive outcomes will occur across life domains". This was assessed using the Life Orientation Test-Revised, which asks participants to rate their agreement with 10 statements such as "I usually expect the best" or "It's easy for me to relax" giving a total score of 0-24.
The Veterans' study assessed optimism based on attributions, said to be "inferred from one's explanations for prior events". This was assessed using the Revised Optimism-Pessimism Scale, which assesses over 200 items rating people on a scale from optimism to pessimism.
The researchers assessed the link between optimism score and survival. They looked at general life span and "exceptional longevity" – living more than 85 years.
They excluded people who died within the first 2 years of doing an optimism assessment to try and rule out the possibility of declining health influencing their optimism (reverse causality). This left them with a total 69,744 women and 1,429 men.
The researchers took into account these potential factors that might have influenced the results: ethnicity, marital status, own and spouse's educational level, depression, long-term conditions such as diabetes and high blood pressure, and lifestyle factors such as diet and smoking.
In the 10 years following the nurses' optimism assessment, 13% of the cohort died. In the 30 years following the veterans' optimism assessment, 71% died. The researchers found that people with higher optimism scores generally tended to have higher educational levels, were less likely to have long-term health conditions, less likely to drink alcohol and more likely to exercise.
After adjusting for all confounders, the highest versus lowest quartile of optimism was associated with an 8.7% longer life span (95% confidence interval [CI] 5.8% to 11.6%) among the nurses, and a 9.8% longer lifespan (95% CI 0.3% to 20.3%) among the veterans.
The researchers report increased chance of surviving beyond 85 with the highest level of optimism: 50% increased chance for nurses (OR 1.5, 95% CI 1.2 to 1.7) and 70% increased chance for men (OR 1.7, 95% CI 1.1 to 2.6). However, these results were from a model where the researchers did not take health behaviours into account. Once the researchers had adjusted for factors like smoking and diet these results were not statistically significant.
The researchers concluded: "Given work indicating optimism is modifiable, these findings suggest optimism may provide a valuable target to test for strategies to promote longevity."
Many previous studies have investigated the question of whether optimism is linked with improved health and lifespan. And the consensus is there is a positive association. This latest study supports this consensus, but does not really stand out as strong, conclusive evidence to end all further debate.
The study cannot prove direct cause and effect. Many hereditary, health, lifestyle and personal circumstances may influence both a person's lifespan and their outlook on life. The analyses tried to adjust for many of these but it is difficult to fully account for all influencing factors.
Optimism is in many ways an abstract concept. It was assessed using 2 recognised questionnaires, but it is difficult to know how well they can capture all the nuances of a person's nature and sense of wellbeing.
The study assessed very specific groups of US citizens: majority white, female nurses and male veterans. It cannot be assumed these participants represent everyone.
It's also uncertain how relevant these assessments are to people today. For example, how applicable the optimism of US war veterans in the 1980s and its relation to their lifespan, is to young adults today.
Despite the researchers' suggestion that "optimism is modifiable", it's not always easy to change your outlook. Optimism may be influenced by both your inherent nature and your life circumstances.
That said there are things you can try to help you cope better with life's ups and downs. If you are struggling with feelings of low mood it's also important to contact a health professional or talk to someone who can help you access support.