Teenage pregnancies are on the rise worldwide and result in several medical problems [1,2]. Teenage pregnancy is highly risky and likely to be accompanied by anemia, premature birth, low birth weight, and gestational hypertension. Teenage pregnancies increase medical and social costs, and they are a huge social problem.

Recently, the coitus experience of high school students in South Korea is increasing. According to the Korea Youth Risk Behavior Web-based Survey (KYRBWS), 6.2% of high school students has coitus experience in 2014. This percentage increased to 7.3% in 2020. Consequently, sexual disease transmission rates among high school students have also increased.

In a survey of single mothers, the percentage of single teenage mothers increased from 49.9% in 1999 to 53.3% in 2001 in South Korea. Among single teenage mothers, those aged 15 years or younger accounted for 6% in 1999, 8.7% in 2000, and 8.3% in 2001. In 2005, the sexually transmitted infection rate among runaway teenagers was 22.3% [3]. Teenage pregnancy is an important public health issue as it increases the economic burden and lowers educational attainment [4].

It is crucial to study the association of sexual behaviors in high school students to prevent teenage pregnancies and associated disease - anemia, premature birth, low birth weight, and gestational hypertension, etc.

So, we investigate the associated factors for sexual behaviors in high school students using data from the 16th KYRBWS, which is conducted annually to assess the prevalence of risky health behaviors among middle and high school students in South Korea.

This study was performed according to the ethical standards of the Declaration of Helsinki and was approved by the Keimyung University Dongsan Hospital Institutional Review Board (IRB No. 2021-07-005).

Data collection was based on the 16th KYRBWS, which was developed and conducted by the Korea Centers for Disease Control and Prevention. It was conducted nationwide between August and October 2020. The 16th KYRBWS is a web-based survey using a complex sampling design [5]. It consisted of 15 areas, including smoking, alcohol consumption, physical activity, diet, weight management, mental health, safety cognition, oral health, self-hygiene, sexual behavior, atopy and asthma, drug, internet addiction, health equity, and violence. There were 103 survey questions, and the participants entered data anonymously online using a computer. All surveys were conducted through questionnaires, and questions about academic and economic status were also asked about the degree to which they thought. The 16th KYRBWS included 400 schools, and there were 57,925 students in total, among whom 54,948 middle school and high school students completed the survey. The participation rate was 94.9%. The 16th KYRBWS was stratified into 44 regions. There were 117 strata in the survey. This study focused specifically on high school students. The total number of high school students was 25,592, with 13,325 male and 12,267 female students. The questionnaire was about sexual behavior, alcohol consumption, smoking, drug intake, mental health, physical activity, weight management, health equity, and other topics.

All statistical analyses were performed using a complex sampling design. The base characteristics of the participants were evaluated using the t-test or chi-square test. Logistic regression analysis was used to confirm the relationship between sexual experience and other factors. Statistical analyses were performed using SPSS (version 21.0; SPSS Inc., Chicago, IL, USA).

Among the 25,592 students included in this survey. The number of students who had sexual intercourse was 1,904, and the weighted percentage was 7.3% (males: 9.2%, females: 5.1%). The students with no sexual experience group had a lower body mass index (BMI) and lower physical activity. Sleep time was longer in the sexual experience group. Students with poor health and happiness perceptions were associated with sexual experience. Feelings of sadness, suicidal thoughts, alcohol consumption, smoking, and drug use were associated with experience. Sex education was not associated with sexual experience (Table 1).

The association between academic performance and sexual experience exhibited a J-curve. Low economic conditions were associated with sexual experience among female students. A J-curve association was determined between economic conditions and sexual experience in male students (Fig. 1).

In our study, the factors in the logistic model were selected using the backward method. Other factors were insignificant in the logistic regression model. Smoking was the most common associated factor for sexual experience among male students (odds ratio [OR]: 4.041, 95% confidence interval [CI]: 3.438–4.751). Short sleep times, high physical activity, feelings of sadness, alcohol consumption, drug use, and good economic status were other identified associated factors in male students (Table 2).

The most common associated factor for increased sexual experience among female students was smoking (OR: 6.525, 95% CI: 5.102–8.345). Low BMI, high physical activity, feelings of sadness, suicidal thoughts, alcohol consumption, and low economic status were other identified associated factors in female students (Table 3).

This is a study to determine associated factors for sexual intercourse in high school students in South Korea. In our study, BMI was associated with sexual experience. Males with a normal weight were most likely to engage in coitus. Meanwhile, females with a lower BMI were more likely to engage in coitus. BMI was also a significant associated factor for female students based on the logistic regression model. This tendency was also observed in another study [6]. This was attributed to the sensitivity of women to weight and courtship behavior [7]. In addition, female students with boyfriends were more likely to engage in coitus [8,9].

Lower sleep time was another associated factor with increased sexual experience seen in male students. Many studies have shown that a lower sleep time negatively impacts teenagers’ health. Short sleep duration influences depression, academic failure, behavioral issues, and aggressive behavior [10-13]. And low academic status and aggressive behavior are associated with coitus experience [6]. So it is possible that this association may have reduced sleep time.

Physical activity was a significant associated factor for sexual experience based on the logistic regression model (OR: 1.108 in males, 1.086 in females). Several studies have shown that exercise increases sexual desire [14,15]. However, only a few studies focused on adolescents. The relevant mechanisms behind this observation are likely to be similar between adolescents and adults. However, further studies are needed to confirm this hypothesis.

Sadness was an associated factor influencing sexual experience in both male and female students. Other studies have reported that depression is associated with sexual experience [16,17]. But suicidal thoughts were not associated factor with sexual experience for male students, unlike for female students. Vasilenko [17] reported that depression affected the sexual experience of females more than that of males. This difference could influence the results of our study.

In our study, alcohol, smoking, and drugs were found to increase the association of sexual intercourse. Abuse of these substances is known to be associated with antisocial tendencies in adolescents [18,19]. Antisocial tendencies are known to be associated with an increase in teenage sexual experiences [20]. These relationships could influence our result. Therefore, adolescents with these associated factors are predicted to have a high association of teenage pregnancy and sexually transmitted diseases.

In our study, sex education does not appear to have any effect on the sexual experience of high school students. But, previous studies have found that sex education suppresses sexual experience [21]. These differences may be due to cultural differences or differences in sex education. According to our study, the current sex education in South Korea is presumed to be ineffective in suppressing the sexual experience of high school students, and a deep consideration is required for the current direction of sex education.

Interestingly, high economic status in boys and low economic status in girls were found to have association with sexual experience. In the case of female students, there is a previous study stating that a low socioeconomic status increases the association of teenage pregnancy [22]. However, according to the results of our study, in the case of male students, the association of sexual experience was high not only in those with low economic status but also in those with high economic status (Fig. 1). Therefore, it should be recognized that, unlike female students, the association of sexual experience may be high for male students with high economic status.

A poor health status was associated with sexual experience. Teenage sexual intercourse can cause several medical diseases - anemia, premature birth, low birth weight, and gestational hypertension, etc [1,2]. But depression, tobacco, and alcohol also associated with health status and sexual experience. Therefore, these confounding factors should be considered to interpret this result.

This study has some limitations. As our study had a cross-sectional design, causality was not established. Therefore, only associations were confirmed by this study. And the information of this study was collected through self-reporting. This can lead to reporting errors and biases. However, the KYRBWS contained numerous samples and was representative of South Korean high school students. The results of our study can be used as a primer to understand the sexual behaviors of adolescents. Moreover, this will help address problems in adolescent sexual behavior.