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.
Short term, lack of sleep scrambles our mental functioning. Long term, the health consequences can be dire. What’s stopping us from getting enough?
For many, adequate sleep is elusive because of sleep disorders, including varieties of insomnia. For others there are practical challenges – baby care or night shifts, for example. A new study focuses on another major, yet strangely overlooked, reason – bedtime procrastination. You want to go to bed early. You know you need to get to bed. And yet you stay up watching TV, playing video games or working late.
Floor Kroese and her colleagues surveyed over two thousand people (age range 16 to 93) in The Netherlands about their sleep habits and self-control. The participants also kept a seven-day sleep diary. All were free from medical sleep disorders or night shift jobs. Overall, the group averaged 7.2 hours sleep a night, but 17.5 per cent of them felt certain they didn’t get enough sleep in general, and over 50 per cent believed they didn’t get sufficient sleep on two nights or more a week.
Looking at the factors that were associated with insufficient sleep, demographics such as age and gender accounted for 8 per cent of the variation in sleep (being younger and female went hand in hand with less sleep), and external factors outside of one’s control accounted for an additional 4.6 per cent. But the headline result is that 12.7 per cent of variation in sleep was explained by self-confessed bedtime procrastination – choosing to engage in activities even though it was time for bed. Lack of self control in general was also associated with insufficient sleep, but this was at least partly explained by co-occurrence of low self-control and greater bedtime procrastination.
“It can be speculated,” the researchers said, “that people who have low self-regulation skills are more likely to keep watching the late night movie, or play yet another computer game despite knowing they might regret it the next morning when waking up tired.”
Kroese and her team are careful to say this is speculation because their methodology does not prove there is a causal role for low self control and bedtime procrastination. It’s possible – indeed likely – that lack of sleep adversely affects self control, thus increasing bedtime procrastination. Nonetheless, it makes sense that the causality runs in both directions and that lack of sleep is for many a self-regulation problem.
If so, the researchers point out that this self-regulation perspective puts lack of sleep “on par with other health behaviour problems such as getting too little exercise, or making unhealthy food choices.” This has implications not just for how we understand the problem, they explained, but also for highlighting potential interventions that could be borrowed from these other areas, such as the use of “if-then” plans. These rehearsed plans help overcome unhelpful habits by setting up new automatic routines or rules – such as, “if I’m feeling tired, then I will switch off the TV”.
_________________________________ Kroese, F., Evers, C., Adriaanse, M., & de Ridder, D. (2014). Bedtime procrastination: A self-regulation perspective on sleep insufficiency in the general population Journal of Health Psychology DOI: 10.1177/1359105314540014
Believing that you’ve had a good night’s sleep can influence your mental performance, regardless of how much sleep you actually had. That’s according to a new paper, by Christina Draganich and Kristi Erdal, who tricked students into thinking there’s a medical technique that can establish objectively how well you slept the previous night.
Fifty students first said how well they’d slept. Next, they were wired up to measures of their brain waves, pulse and heart-rate, and half of them were told the fiction that in fact they’d had just 16.2 per cent REM sleep the previous night (below average sleep quality); the other half were told they’d had an above average night of sleep, with 28.7 per cent REM sleep. Confronted with a difficult mental arithmetic task, the students told they’d had a good night’s sleep then outperformed those who were told they’d had a poor night’s sleep. In contrast, their initial subjective sense of their previous night’s sleep quality was not related to their performance.
It might be tempting to take from this first result the idea that we can boost our mental performance if we convince ourselves we slept well last night. However, bear in mind that the students told they’d had a good night’s sleep scored 34.81 on average on the arithmetic test, whereas the average score on this test for an adult is 36. It’s a shame there wasn’t a baseline control condition to see how students would have performed without receiving any information about their sleep quality. Those students told they had a bad night’s sleep scored 22.13 on the test. If anything then, this first result looks like a “nocebo effect”: belief that last night’s sleep was bad undermined performance, but being told last night’s sleep was good made little difference.
A second study was similar but this time, after receiving fictitious positive or negative feedback on their previous night’s sleep, dozens of students completed a range of tests: the same arithmetic task used earlier, a word association task, a measure of visual-motor processing speed, and a digit-span test of short-term memory. Another improvement from the first study is that the researcher who interacted with the participants did not know which condition they’d been allocated to. There were also two control groups – they answered questions about their sleep the previous night and then performed the tests. So they didn’t receive the false “objective” feedback on their sleep quality.
For those who received it, feedback on sleep quality was correlated with performance on the arithmetic task and the word association task, with those told they’d slept well scoring higher than those told they’d had a disturbed night. The students’ initial sense of how well they’d slept, before they received the objective sleep measure, was not correlated with their performance on any of the tests. This was also true for the students in the two control conditions.
This time there was some evidence of a beneficial placebo effect. Students told they’d had a good night’s sleep scored an average of 51 on the word association task, whereas the adult average score on this test is 43.51. It’s shame the researchers didn’t provide the word association scores for the students in the control conditions for comparison. Their scores could have acted as a baseline rather than referring to published adult norms for the tests.
“We have shown that decrements in performance can be elicited when verbal instruction and technological displays convey poor sleep quality to the individual,” the researchers said. “We have also shown that increments in performance can be elicited when verbal instruction and technological displays convey high-quality sleep.”
These results build on a study published ten year’s ago that found people with insomnia experienced less sleep-related anxiety when a real objective measure of sleep (an actigraph) showed that they tended to overestimate how long it took them to get to sleep.
_________________________________ Draganich C, and Erdal K (2014). Placebo Sleep Affects Cognitive Functioning. Journal of experimental psychology. Learning, memory, and cognition PMID: 24417326
Forget counting sheep or popping pills, a team of Dutch researchers have reported the profound sleep-inducing effect of a warming body-suit.
Eight young adults and sixteen older adults, half of whom suffer from insomnia, spent two nights in a body-suit at a sleep laboratory (see image), with a night at home in between.
Water-filled micro-pipes in the suit maintained the skin temperature of the participants at either 35 degrees celsius in the cool condition or 35.4 degrees in the warm condition, fluctuating gradually between the two every 15 to 30 minutes. Importantly, core body temperature was unaffected by these subtle temperature fluctuations.
The controlled skin temperatures match the typical climate of a person’s bed and are close to the levels that people report to be of most comfort, with the warmer condition actually reported to be slightly less comfortable.
Recordings of the participants’ brain waves at night showed that warmer skin temperatures resulted in a shift in sleep depth towards deeper sleep and a reduction of their likelihood of being awake at 6am.
For instance, among the non-insomniac older participants, a subtle (only 0.4 degree) increase in skin temperature reduced the probability of being awake at 6am by a factor of 14; for those with a sleep problem, it was by a factor of five. Moreover, with the same subtle increase in temperature, the likelihood of an older insomniac participant being in a deep (slow wave) sleep was doubled for any point in the night.
Roy Raymann and colleagues who conducted the research believe skin temperature affects cells in the hypothalamus of the brain that are responsible for controlling sleep.
The findings have huge practical implications, even before the development of user-friendly body-suits. For example, it is possible that the temperature environment people choose to sleep in, based on comfort, may not be optimal for inducing sleep.
A warm bath before bedtime could help increase skin temperature at the start of the night, and a timed electric blanket could be used to increase skin temperature in the morning. Thick blankets or an all-night electric blanket won’t help because they will simply cause overheating, especially of core body temperature, which will disrupt sleep.
“The effects of even very minimal temperature manipulations within the thermoneutral comfortable range are so pronounced that they warrant further research into practical thermal manipulation applications to improve sleep,” the researchers concluded. _________________________________
Raymann, R.J., Swaab, D.F., Van Someren, E.J. (2008). Skin deep: enhanced sleep depth by cutaneous temperature manipulation. Brain, 131(2), 500-513. DOI: 10.1093/brain/awm315
From ‘The Archives’, first published in the Digest 2/2/2004
For the 33 percent of Americans who suffer from insomnia, a good night’s sleep is no more than a dream. Part of the their problem could be that they overestimate how long it takes them to get to sleep, thus sustaining a self-perpetuating cycle of sleep-related anxiety.
Nicole Yang and Alison Harvey (Oxford University) recruited 40 students with primary insomnia from two Oxford universities. All the participants said that for at least a month they had suffered difficulty sleeping as frequently as three nights per week.
The participants were kitted out with a watch-like gadget – an actigraph – that provided an objective measure of sleep, based on how much they tossed and turned in the night. For three nights they wore the gadget and kept a sleep diary. Afterwards, half of the participants were shown, based on the actigraph’s measurements, how they had overestimated in their diary how long it took them to get to sleep. The procedure was then repeated for a further three nights.
For the second three-night session, the participants who had seen the discrepancy between their own and the actigraph’s measure of how long they took to drift off, now estimated this period more accurately and reported significantly less sleep-related anxiety than did the other participants.
“The findings support the proposal that distorted perception of sleep functions to maintain insomnia by fuelling anxiety and preoccupation with sleep” the authors claimed. And use of an actigraph “provides a non-intrusive, easy to administer method” of correcting these distortions. __________________________________
Just thinking that they’ve not had much sleep could interfere with the daytime functioning of imsomniacs, regardless of whether they actually had enough sleep or not.
Twenty-two students (average age 21 years) with primary insomnia were recruited by Christina Semler and Allison Harvey at Oxford University. All had experienced at least three nights’ sleep disturbance per week for the past month.
For three nights, the students’ sleep was measured using a sensitive gadget that records how much its wearer moves around. Each morning, an electronic display that the students thought was connected to this gadget, told them how well they had slept. But in fact the display was controlled by the researchers, so that they could trick the students into thinking they’d had a good or bad night’s sleep, regardless of how well they’d actually slept.
On days that the students were led to believe they’d had a poor night’s sleep, they reported having more negative thoughts (e.g. “I can’t cope today”), feeling more sleepy, performing more sleep-related monitoring (e.g. noticing aching muscles/ sore eyes), and resorting to more compensatory behaviours (e.g. taking a daytime nap). That’s despite the fact that the actual quality of their sleep didn’t vary significantly between days they were given positive or negative feedback about their sleep.
Together with past research showing imsomniacs often sleep much better than they realise, these findings suggest it could be their anxiety about not sleeping well, rather than a lack of sleep per se, that causes or worsens the daytime impairments so often reported by imsomniacs.
If these results can be replicated with a clinical sample, the authors said, then “…consideration should be given to teaching insomnia patients to lend less credence to their subjective perception of sleep. And the adverse consequences, for daytime functioning, of concluding that they’ve not obtained enough sleep should be emphasised”.
Semler, C.N. & Harvey, A.G. (2005). Misperception of sleep can adversely affect daytime functioning in insomnia. Behaviour Research and Therapy, 43, 843-856.