Positive psychology has become more prominent in recent years, as empirical evidence confirming the influence of positive psychological variables such as happiness on well-being continues to emerge [1]. Happiness has been broadly used to describe positive subjective experiences, and is often said to comprise two components: the cognitive appraisal of one’s life and affective evaluations (both positive and negative), which are viewed as separate dimensions [2].

Research on happiness has suggested that higher levels of happiness have multiple health benefits, such as a reduced risk of morbidity, disability, and mortality [3]. One possible explanation for the health outcomes of happiness may be that positive well-being may be accompanied by health behaviors that reduce the risk of disease and promote health. Since approximately half of cancer deaths could be prevented by improvements in health behaviors and environmental factors, the investigation of associations between happiness and health behaviors may prove helpful in developing cancer prevention strategies [4].

Although substantial evidence exists that health behaviors are associated with negative mood states, the relationship of healthy lifestyles with happiness is less well established [5,6]. While associations between self-reported happiness and refraining from smoking, lower alcohol consumption, high levels of physical activity, and a healthy diet have been documented in several studies [7], the underlying mechanisms of these effects are still subject to debate, as findings vary among countries, especially between developed and developing nations [8].

Happiness is considered to be particularly important in adolescents, due to its contribution to their future success [9]. However, few studies have investigated adolescent health behaviors in relation to happiness from their perspective. Therefore, after adjusting for known socioeconomic factors, we examined associations between happiness and a wide range of health-related lifestyle behaviors, such as smoking, drinking, eating breakfast, eating fruits and vegetables, physical activity, sedentary behavior, and hours of sleep among South Korean (here after Korean) adolescents. We predicted, on the basis of previous findings, that being a non-smoker or non-drinker, eating breakfast, eating fruits daily, vegetable consumption, participating in physical activity, engaging in less sedentary behavior, and sufficient sleep would be associated with higher levels of happiness.

The sample consisted of 72,435 Korean adolescents between 12 and 18 years of age, 47.7% of whom were girls. Of the respondents, 58.2% perceived themselves as happy (very happy or a little happy). According to sex, the happiness level of boys was significantly higher than that of girls. Approximately 9.7% of adolescents smoked currently and 16.3% were current drinkers. Three-fourths of respondents had breakfast more than three days per a week, and only one-fifth ate fruits daily. The proportion of participants who consumed vegetables more than three days per a week was 16.6%. Approximately 30% of adolescents participated in at least 60 minutes of physical activity more than three days per a week, while 66.3% of them spent more than 2 hours a day watching TV or videos or playing computer or video games in their leisure time. More than 8 hours of sleep were reported by 21.8% of respondents on weekdays and 66.3% on weekends. The health behaviors that showed differences according to sex were current smoking, current drinking, eating fruit daily, vegetable consumption, physical activity, sedentary behavior, and hours of sleep (Table 1).

Table 2 provides aORs for the associations between happiness and current smoking, current drinking, eating breakfast, eating fruit, vegetable consumption, physical activity, sedentary behavior, and hours of sleep by sex. The results indicate that both boys and girls who were happier were less likely to smoke or drink. Girls who were happy were more likely to eat fruit daily and less likely to exhibit sedentary behavior, while boys did not show a significant association between happiness and these behaviors. In contrast, boys who were happy were more likely to participate in physical activity, though no significant relationship was found between happiness and physical activity among girls. Regarding eating breakfast, vegetable consumption, and sleeping patterns, adolescents who perceived themselves as happier were more likely to have healthier lifestyles regardless of sex.

This study was conducted to explore the associations of happiness with health-related lifestyle factors in the Korean adolescent population using a web-based questionnaire survey. The main hypotheses were largely confirmed. Multivariate analysis of the survey data demonstrated that self-reported happiness was significantly associated with the absence of current smoking or drinking, eating breakfast, eating fruits every day, vegetable consumption, participating in at least 60 minutes of physical activity a day, sedentary behavior, and hours of sleep. Additionally, sex differences were found in the relationships between happiness and eating fruit every day, participation in physical activity, and sedentary behavior.

The proportion of adolescents in our study who reported that they were very happy or a little happy with their lives was 58.2%. This proportion was noticeably lower than has been found in Western populations. In a Norwegian survey targeting adolescents participating in a World Health Organization project, the proportion of happy individuals was approximately 90% [9]. In another survey targeting Japanese adults, the proportion of participants reporting being happy was found to be only 48.4% [20]. In contrast, a nationwide survey of US adults reported an overwhelming majority of happy individuals (94.8%) [13]. Further, a previous study found that the probability of being in a depressed mood was greater in collectivistic than in individuaistic cultures [21]. Thus, these findings seem to suggest the presence of lower levels of self-reported happiness among individuals in collectivistic societies such as Japan and Korea relative to individualistic Western societies.

Our results indicated a negative relationship between happiness and smoking or drinking in both boys and girls. These results correspond to previous findings [22]. Adolescents who are not satisfied with their lives smoke and drink more often than those who do not experience these feelings. Our findings also suggest that the associations were stronger in girls than in boys, perhaps because girls are more sensitive to emotional events or problems [23].

Consistent with previous reports, this study suggests the presence of a positive correlation between happiness and a healthy diet [7,24,25]. Kawada et al. [24] previously found that eating breakfast was negatively related to depressive states, supporting our present findings. Our study also found that girls who were very happy ate fruits daily, and both boys and girls who were very happy consumed vegetables more than three times per day. Psychological comfort may lead a person to pay more attention to his or her health and the health value of certain foods. The broaden-and-build theory suggests that positive emotions may trigger an upward spiral that could reinforce positive behavioral patterns such as healthy eating [26]. The sex differences found in associations between happiness and eating fruit daily may be due to the relative lack of concern for health and the lower consumption of fruits among boys relative to girls [27].

With respect to the relationship between happiness and physical activity, we found that boys who were very happy were more likely to participate in at least 60 minutes of physical activity, while a significant association was not found for girls. One possible explanation may be that many girls do not engage in sports, but instead have social interactions outside the sphere of athletics. While several studies have found relationships between reduced participation in sports and emotional difficulties in boys, few have tested for an interaction between sex and sport participation [22]. Contrary to the results for physical activity, the perception of happiness in boys was not related to sedentary behavior, though girls who felt happier were less likely to report sedentary behavior. This may be explained by the fact that boys are less active and tend to enjoy computer games much more than girls, regardless of emotional status.

Our study provided evidence suggesting that happiness may be significantly associated with sufficient sleep, which is consistent with previous findings [28]. Prior research on stress and sleep has focused on the negative consequences of poorer mental health status on sleep disturbance. Zhou et al. [28] demonstrated a longitudinal relationship of stress disorders with sleep problems in adolescents. However, the causal relationship between cognitive and emotional mood and duration of sleep needs to be further clarified, this cross-sectional study suggests whether happiness can totally lead to sufficient sleep in adolescents or not.

The causal pathways linking happiness with health behaviors are still not clear. Bidirectionality is probably involved in the potential relationship between happiness and health behaviors. Several longitudinal studies have suggested that serious and persistent negative emotions were prospective predictors of increased smoking, and, similarly, heavy smoking predicted the subsequent development of depressive symptoms [23]. Previous results of lagged analyses also revealed that consuming fruits and vegetables predicted improvements in positive affect the next day, while, on days when young adults experienced greater positive affect, they reported eating more servings of fruit and vegetables [25]. A similar pattern was found in the area of physical activity. An analysis of the Prospective National Population Health Survey revealed that a change in the status of leisure-time physical activity from active to inactive was associated with increased odds of becoming unhappy two years later [29]. Regarding sleep duration, several longitudinal studies have shown a predictive relationship between disordered sleep and subsequent depression across various populations [30]. Future research should include randomized controlled trials evaluating the influence of happiness on health behaviors in adolescents.

This study had several strengths, including its use of a national representative sample and consideration of a wide range of lifestyle factors. It was also novel in its analysis of adolescents living in Korea, where some of the highest suicide rates in the world have consistently been reported. It had several limitations as well. This study was cross-sectional, so cause–effect relationships could not be confirmed. Our findings were based on self-reports of happiness assessed using a single item; therefore, some of the responses may not have been entirely reliable. With this in mind, a study evaluating the development and evaluation of happiness scales for adolescents could be a next step for future research. Additionally, it is possible that other factors contributed to associations between happiness and health behaviors, such as personality, social environment, or genetic factors. Thus, several additional unmeasured variables may have contributed to the relationships between happiness and health behaviors that we observed. Nevertheless, most importantly, this study demonstrated a meaningful link between two distinct areas of adolescent health research: the literature on happiness levels and the literature on health-related lifestyle factors. Research bridging these two areas is limited, and it is therefore notable that this study identified significant relationships between self-reported happiness and health behaviors.

The present study found that happiness was related to a variety of health behaviors among Korean adolescents, including the absence of current smoking or drinking, eating breakfast, eating fruits daily, vegetable consumption, participating in at least 60 minutes of physical activity a day, sedentary behavior, and hours of sleep. These results encourage public health professionals to take into account the psychological aspects of adolescent life in working to improve their health behaviors and outcomes. Public health strategies promoting health-related lifestyle behaviors among adolescents may easily be improved by encouraging adolescents to appraise their own lives in a positive manner.