Is there any relationship between sleep and happiness?
It is known that depressed people often sleep too much. Other depressed people have a hard time sleeping. We also know that, on the whole, happy sleep better. Or maybe it is that people who sleep better are happier. We’ll return to this question later. For now, we report the results of a study out of South Korea that asked over 72,000 teenagers about their lives. The survey asked the teens about their lifestyles, especially diet, exercise, and sleep.
Happiness in Korean Teens
The Korea Youth Risk Behavior Web-based Survey (KYRBWS) has been administered to middle- and high-school students every year beginning in 2005. The results of the happiness study were based on the 9th study, administered in June-July 2013.
Students were asked at random to participate in the study. They were given the option to decline, including at the beginning of the survey.
A single question was asked about the teen’s happiness: ‘In general, how would you describe your happiness?’ Predefined responses were ‘very happy’, ‘a little happy’, ‘neutral’, ‘a little unhappy’, and ‘very unhappy’.
The investigators note that this single question is good enough to assess the truth of the teen’s overall happiness. Nevertheless, one can ask whether the question could be interpreted as “are you happy today?” as opposed to “are you in general a happy person or not?” It’s a little like asking someone what the whether is like where they live. If it happens to be a beautiful day, I suspect the subject’s feelings about the weather would be more positive than if there were a thunderstorm that day.
Nevertheless, the investigators went ahead, and asked a number of demographic and lifestyle questions.
The survey then asked a number of questions about diet, exercise and health habits. For example, the teens were asked whether they had consumed alcohol or smoked a cigarette in the previous 30 days. If they answered yes, they were classified as a current drinker or smoker. Specific questions were asked about physical activity and fruit consumption.
The students were also asked about screen time, including television watching and video game playing.
Sleep and Happiness
Students were asked about their sleep on both weekdays and weekends. The investigators divided the answers into two groups: students who slept fewer than 8 hours per night, and those that slept more than 8 hours.
The data were analyzed by a statistical device called “adjusted odds ratio”. This is simply the association between an exposure and an outcome. The investigators compared “exposures” such as hours of sleep, to the outcome “happiness”. They took the group of teens who described themselves as “very unhappy” and assigned them the value of 1. If more sleep meant the teen rated herself as happier, the odds ratio would be greater than one. If the correlation ran in the other direction, the odds ratio might be less than one.
Korean Teens are not very happy
There were a couple of interesting observations coming out of this study. The proportion of teens in the study who reported that they were very happy or a little happy with their lives was only 58.2%. In comparison, 94.8% of American adults say they are very or a little happy. That’s a fairly stunning difference. The investigators believe the happiness gap can be explained by the cultural difference between “collectivist” societies like Korea’s, and an “individualistic” society such as in the US. The truth is probably more complex than this.
Korean Teens don’t sleep a lot
The survey revealed that Korean teens spend a lot less time asleep than do American Teens. Overall, 21.8% report getting more than 8 hours of sleep on weekdays, and 66.3% sleep more than 8 hours on weekends. By contrast about half of American teens get 8 hours or more of sleep on weekdays, with substantially larger percentages on weekends. Again, the reasons for the disparity are probably complex.
More sleep, more happiness
The investigators found that the more Korean teens slept, the more likely they were to rate themselves as happy. If a girl reported more than 8 hours of sleep on weeknights, the odds ratio was 3.00 that she’d rate herself “very happy”. In other words, she was statistically three-times more likely to call herself “very happy” as opposed to “very unhappy”. For a boy, the odds ratio was 2.32. It’s worth mentioning here that odds ratios of more than 2.00 are thought of as meaningful. Even though lower odds ratios may be real and statistically significant, anything the difference might not be “clinically significant”. In other words, lower odds ratios make you say “so what? In real life you can’t really see much difference!”
On weekends, the odds ratios were smaller. Girls who slept more than 8 hours had an odds ratio of 1.63 for self-rating “very happy”. For boys the odds ratio was 1.72. This result suggests that more “unhappy” Korean teens were sleeping >8 hours on weekends, possibly in an attempt to make up their sleep debt.
Sleep and Happiness; Chicken and Egg
A big weakness of this study is that it shows only associations. It cannot show causes. So at the end of the day we cannot really know why Korean teens who sleep more rate themselves happier. Are they happier because they sleep more? Or do they sleep more because they are happier?
Looking at the study as a whole, however, we can begin to unravel the “which came first?” problem. It turns out that other positive health habits correlate with happiness as well, such as healthy eating and exercise. And negative health habits such as smoking and drinking tend to correlate with unhappiness. Again, we can’t really be sure which came first, but the results as a whole are compelling.
- Sleep and Happiness in Korean teens are associated with one another.
- Less sleep is associated with smoking, drinking and less happiness.
- More sleep may help teens feel better about themselves.