Adolescence might be critical for later health and disease,1 because there is some evidence stating that habits acquired in this period may track into adulthood. For instance, alcohol habits during adolescence increase the likelihood of heavy consumption in adulthood,2 as well as food consumption in adolescence is a predictor of intake in adulthood.3 For this reason, several chronic diseases may have their origin, and disease progression, during adolescence.1

To improve adolescents’ health, it is important to promote healthy behaviors at an early age, especially during adolescence. Healthy behaviors are a determinant of health; positive changes can have an impact on the overall health outcomes.4 The main behaviors associated with adolescents’ health are physical activity, less time engaging with multi-media, healthy diet, and absence of alcohol and tobacco consumption,4–6 as well as caffeine/stimulant use, sleep deprivation, drug use, condomless sex, and unhealthy relationships.7 During the transition into adolescence and throughout it, there is an increase in desiring novelty, along with the courage and curiosity to experiment with new and often unhealthy behaviors.8

Since adolescence is a critical time to establish the foundations of a person's health,1,2 it is important to understand the behavioral practice during the transition from early to late adolescence. Studies on adolescents’ healthy habits have focused on the relationship between individual behaviors and their outcome on health.9,10 Attempts to combine several health behaviors to create a solution to express a healthy lifestyle are sparse.11 Such measure could be important to the public health policy by influencing the way in which programs set up to promote healthy lifestyles are developed. Thus, there is a need to understand how healthy behaviors, and a healthy lifestyle, change during this stage of life. Therefore, using a wide and representative sample of adolescents from 37 countries and regions, this study aimed to examine the association between age and changes in self-reported prevalence of healthy behaviors in adolescents.

The characteristics of the sample data are presented in Table 1. Most of the adolescents lived with their mother (94.1%), 77% lived with their father at home, and more than 80% had siblings. Only 5% were classified as having a lower socioeconomic status, while the remaining were classified as medium (34.7%) or high (60.3%) socioeconomic status.

Table 2 presents the prevalence of healthy lifestyle behaviors. Among boys, screen time less than 2h/day (12.8%, 95% CI: 11.7, 14.0), eating fruit and vegetables every day (16.2%, 95% CI: 15.1, 17.3), and practice of physical activity every day (18.9%, 95% CI: 17.8, 20.0) were the least prevalent healthy behaviors at the age of 15 years. In turn, the prevalence of boys who did not consume alcohol (89.1.5%; 95% CI: 88.6, 89.6) and did not smoke (97.3%; 95% CI: 97.1, 97.5) was higher at age 11. The prevalence of all healthy behaviors significantly decreased with age, and the decreasing trend was more pronounced regarding alcohol consumption (−43.5%; 95% CI: −44.1, −42.8) and smoking (−21.6%; 95% CI: −22.1, −21.0) than regarding physical activity, screen time less than 2h/day, and eating fruits or vegetables every day. Only 4.7% (95% CI: 3.4, 6.0) of boys aged 11 years had a healthy lifestyle. The figures are even smaller at 13 years (3.0%; 95% CI: 1.8, 4.2) and 15 years (1.5%; 95% CI: 0.3, 2.7). This decrease presented a significant trend (−3.3%; 95% CI: −3.6, −2.9).

Among girls, practice of physical activity every day was the least prevalent healthy behavior (9.4%, 95% CI: 8.3, 10.6), followed by screen time less than 2h/day (18.7%, 95% CI: 17.6, 19.8), and eating fruit and vegetables every day (22.6%, 95% CI: 21.5, 23.6) at the age of 15. More than 90% of 11 years girls did not consume alcohol (93.0%; 95% CI: 92.6. 93.3) and did not smoke (98.8%; 95% CI: 98.7, 99.0) at the age of 11 years. However, this prevalence decreases by more than 43% for no alcohol consumption and more than 20% for not smoking. Only 4.4% (95% CI: 3.2, 5.7) of girls aged 11 years had a healthy lifestyle. The figures decrease to 2% (95% CI: 0.8, 3.2) at 13 years, and to less than 1% at15 years. This decrease presented a significant trend (−1.5%; 95% CI: −1.7, −1.3).

The mean of healthy behaviors by country, stratified by age, is presented in Table 3. The mean of healthy behaviors decreased significantly in all countries from age 11 to age 15.

This study aimed to examine the association between age and changes in self-reported prevalence of healthy behaviors in adolescents. As age increased, the prevalence of adolescents with a healthy lifestyle decreased. Only 4.7% of boys and 4.4% of girls aged 11 years, 3.0% of boys and 2.0% of girls aged 13 years, and 1.5% of boys and 0.8% of girls aged 15 scored perfectly on the healthy lifestyle score. Since a healthy lifestyle has a positive impact on health and is essential to prevent early onset of chronic diseases,4 these results show that most adolescents are at risk. The choices in regards to health during adolescence may jeopardize their future health.

Concerning physical activity, a strong decrease in its practice was observed from 11 to 15 years of age. All countries and regions were similar in showing a decrease of physical activity by age. The physical activity decrease by age was also documented in previous studies using objective measures of physical activity.19,20 As adolescents age, they gain more independence and are exposed to other environments and influences (e.g., school and peers). Furthermore, the cost of activities also influences the decrease of physical activity with age. Physical activity during childhood is mostly informal. However, adolescents tend to practice formal physical activity, which has associated economic costs (e.g., membership, purchase of equipment). Thus, among socioeconomically disadvantaged adolescents, there are less opportunities; naturally, the number of participants decreases with age.

In line with previous studies,21,22 screen time behavior increases throughout adolescence. This trend tends to increase given that new media screen time has significantly increased in recent years, especially after smartphones and similar portable devices such as tablets gained over 50% market saturation among adolescents.23 This finding probably reflects two realities for adolescents: increased academic demands and a higher need for social interaction. Nowadays, many screen electronic components might be used as tools to help students with homework and diverse school content.22

The decrease in the consumption of fruits and vegetables in adolescence has been observed,24 and age is considered a determinant factor in this intake.25 The decreasing trend of fruit and vegetable consumption begins in childhood and continues into young adulthood.26 From early to mid-adolescence, this decreasing trajectory stands out from multiple changes in lifestyle, and both physical and environmental aspects that take place in adolescence, such as peer influence or availability in schools.25 The greater freedom in food choice experienced by adolescents and the level of support for fruit and vegetable consumption during this phase might explain the decrease in fruit and vegetable consumption throughout adolescence.24

Concerning alcohol and tobacco use, these behaviors tend to be clustered; trajectories of the consumption of these substances are linked.27 As age increases, the consumption of alcohol and use of tobacco also increases. Among the healthy behaviors, these presented a bigger decrease with age. The same trend had been previously observed,27 meaning that the transition from early adolescence to mid-adolescence is a critical period for alcohol consumption and tobacco use.

The general decrease in the prevalence of healthy behaviors with age shows that adolescents have a lifestyle that harms their health and jeopardizes it in the future. This was clearly demonstrated in the present study, in which less than 2% at the age of 15 had a healthy lifestyle. As demonstrated, adolescents become more independent with age; they start to have different interests, suffer marked influence from peers, and spend more time at school without parent supervision. Thus, interventions are needed to reverse the increase in the prevalence of unhealthy lifestyles. Schools are a gateway to provide adolescents with skills to manage and improve their lifestyle.28 Virtually all adolescents attend school, spending much time there; in schools, they are subjected to the transmission of knowledge that can be used to improve their health. There is evidence that school-based single-component or multicomponent interventions can improve short- and long-term adolescents’ healthy behaviors.24,25,28 Therefore, a large number of adolescents could benefit from these interventions.

This study has strengths and limitations that should be acknowledged. One strong point is that the findings are from an international study comprising 42 countries with the same standardized instruments, which allows comparisons. A noteworthy strength is the fact that only 5% of the participants have low family affluence scale. This gives hope to generalize the findings, because there is not much variation among the adolescents’ socioeconomic status. The HBSC database contains numerous missing values. Over 40,000 adolescents did not report the healthy behaviors and were excluded from the data analysis, because it was not possible to create a healthy lifestyle composite score based on the five healthy behaviors. Data collection was based on self-reported information, which is subject to bias. Furthermore, eating fruits or vegetables daily does not mean the adolescents necessarily consumed the recommended servings. It would be important to accurately measure fruit and vegetable consumption to determine whether it meets the guidelines.15 Lastly, the cross-sectional design precludes a causal inference for the relationship between a healthy lifestyle and age.

Results from this study highlight the fact that there is still much work to be done to promote healthy lifestyles and to raise awareness among adolescents of the potential benefits to their health status. Given that it known that health behaviors are set during this developmental period, understanding how best to promote healthy lifestyles is still of crucial importance during this life phase. It is also important to highlight that the lower prevalence of adolescents with a healthy lifestyle appears to corroborate that unhealthy behaviors tend to cluster.29 Schools also can improve adolescents’ lifestyle through knowledge. It is important to teach adolescents the physical guidelines,13 the health problems associated with time in screen-based behaviors,30 the recommendation for the amount of time that can be devoted to these behaviors,14 the habits of healthy eating, the recommended daily consumption of fruit and vegetables,15,16 and the benefits of abstinence from alcohol consumption18 and tobacco usage. Knowledge may not be sufficient to improve the adolescents’ lifestyles, but having knowledge put into practice could be a step closer to raising awareness of the importance of healthy behaviors, with the intent that the younger generation may make educated decisions about their health.

The authors declare no conflicts of interest.