Your personality traits play an important part in how long you are likely to live, as much as, or even more than, other personal factors like your intelligence and your family’s economic background. Now a study in the Journal of Research in Personality has identified a key factor that mediates the personality-mortality link – sleep. Simply put, people with certain personality characteristics are more likely to sleep too little, or too much, or to experience greater sleepiness during the day, and in turn this raises their year-on-year risk of dying (too little or excess sleep, and poor quality sleep, have known links with various health risks, such as cardiovascular disease, depression and chronic inflammation).
“Sleep has been associated with both personality and longevity, yet [before now] no study has investigated whether sleep is a pathway linking personality to objective health outcomes,” say the researchers, led by Shantel Spears at West Virginia University.
The researchers used data collected from thousands of participants as part of the long-running National Survey of Midlife Development in the United States, including information on their personality traits recorded in 1995-1996, and information on their sleep duration and sleep quality collected in 2004-2006. Nearly 4000 participants provided data at both these time points, and the researchers then used national records to see which of them had died and when, up to October, 2015.
As expected, based on the known importance of sleep to health, the research showed that too little or too much sleep was associated with increased risk of dying – approximately 65 minutes more than, or under, the average nightly sleep duration (7 hours in this sample) was associated with a 10 per cent increased risk of dying over the course of the study.
Turning to personality, and consistent with many prior studies, participants who scored lower on trait conscientiousness were more likely to die before the end of the research period, and Spears’ team established that this was explained in part by these people getting less sleep, on average, and feeling less rested during the day (a mark of poorer sleep quality). Although the study didn’t look into why exactly people low in conscientiousness were getting less sleep, one can imagine they engage in more bedtime procrastination, and generally struggle to establish a healthy bedtime routine.
Similarly, high scorers on trait neuroticism were indirectly at greater risk of dying because of their lower and higher than average amounts of sleep, and their on-average greater feelings of fatigue in the daytime. Again, one can speculate that these folk, who have lower moods and more worry, might struggle to get to sleep or to get up promptly in the morning.
Lower scores on extraversion were indirectly linked with increased risk of death, thanks to an association with greater daytime feelings of fatigue (perhaps extraverts’ greater daytime activity levels makes it easier for them to get a satisfying night’s sleep, but this is speculation). Most surprising – given prior research findings have not identified this trait as being relevant to sleep – was the indirect link between higher trait agreeableness and risk of dying, explained by these people having less sleep and more daytime fatigue; it’s not clear why this might be.
Previous research had already established that personality predicts longevity because of its association with various health behaviours, such as more conscientious people being less likely to smoke, or drink and eat to excess. However, much of the personality-linked variance in risk of dying has remained unexplained, and this study now identifies too little or too much sleep (and feeling insufficiently rested during the day) as other important factors. “Our findings suggest that short and long sleep duration and daytime dysfunction may be important pathways linking aspects of personality to reduced life expectancy,” the researchers said.
The research has some important limitations including the participants being mostly white and highly educated; the reliance on a short self-report test of personality; and the subjective measure of sleep being based on time spent in bed rather being asleep per se. Nonetheless, if the results can be replicated, they raise some important implications for public health, suggesting that personality screening could be used to identify those people – especially high scorers in neuroticism and low scorers in conscientiousness – most likely to benefit from interventions aimed at improving sleep. “Alternatively,” the researchers said, “changing these aspects of personality could improve sleep for these individuals, enhancing their health and longevity”.