To our knowledge, this is the first study investigating body weight and dental caries experience among adolescents using social determinants as common risk factors. The present study demonstrated social inequalities in body weight and dental caries among girls, with poorer outcomes observed among those enrolled in a vocational program compared to those enrolled in a sports and physical education program or a general studies program. Social inequalities in body weight among boys were based on mother’s education, and adolescent’s study program, while in dental caries experience on parents’ employment. In addition, among boys social inequalities in body weight and dental caries were based on demographic characteristic, household composition, with poorer outcomes observed among those living without adults.
This was a cross-sectional study, whose design in general is prone to confounding and does not allow to establish causality [27]. One way to control for confounders is to adopt a multivariable analysis, as was implemented in the present study [27].
The initial participation rate in FF1 was high, reaching 93%, and participation in the oral health part of FF1 was only slightly lower (90%). It is possible that this decrease in attendance to the dental evaluation that constituted the oral health part of FF1 was associated with low parental education, unemployment, and low income [28]. After exclusions due to age and missing data, our final study sample represented 88% of all students invited to FF1, but in multivariable binary logistic regression comparative Model 2, the number of participants was reduced to 57% among girls and 52% among boys due to missing data; therefore self-selection bias cannot be ruled out. The sample was collected from both a densely populated urban area (Tromsø, 7 schools) and a sparsely populated rural area (Balsfjord, 1 school) in Troms County, Northern Norway. In this county, 29% of the population resides in sparsely populated areas; therefore, the population residing in densely populated areas might be overrepresented in the study sample. It has been shown that living in densely populated areas is associated with higher physical activity and thus better health outcomes among adolescents in Norway [24]. It must be noted that 16–18% of adolescents live without parents in Troms County. Indeed, as Troms County is large, adolescents sometimes have to move from where their parents live to where the school is located – creating the household composition of “living without adults”. This living situation occurs due to adolescents’ need for education; not necessarily because they have a higher level of maturity. It has been also shown that having an immigrant background was related to worse general and oral health outcomes among children and adults in Norway [29–31]. In Tromsø municipality in 2012, 4.8% of immigrants were aged 16–19 years [32]. In our study sample 6% of girls and 5% of boys reported that they were born outside Norway, indicating that our sample might be representative of the national population with respect to immigrant background.
A validated, pretested, electronic, self-administered questionnaire was employed to collect data on SEP indicators and most of the covariates. In general, questionnaires are prone to bias, especially regarding sensitive data, like alcohol intake and tobacco use. However, self-administration has been shown to decrease reporting bias [33].
In order to get a global measure of health and health behavior, a composite health/health behavior variable was calculated. It has been shown that composite measures might be the best approach to study socioeconomic differences in health among adolescents [34]. The validity of our composite health/health behavior variable is debatable. On the other hand, less than good health behavior was observed more often among boys than girls (p < 0.05) and among those enrolled in a vocational program compared to those in a general studies program or in a sports and physical education program. This is in line with other studies [34, 35], and therefore the composite health/health behavior variable is likely to be of satisfactory validity. Moreover, construct validity was demonstrated in that the composite health/health behavior variable among girls discriminated significantly in the predicted direction between overweight/obese and normal-weight participants and between participants with high and low dental caries experience.
One of the SEP indicators in this study was mother’s education. Mother’s education was chosen as previous studies have shown it to be associated with child’s health behavior and adverse health events in Norway [36, 37]. There were 108 girls and 145 boys who did not know their mother’s education, mostly those enrolled in a vocational program. This finding is in line with a previous study and might denote the extent of selection bias in the present study, as students with missing values were excluded from the multivariable binary logistic regression analyses [38]. In the Norwegian school system, there is a lawful right, but not an obligation, to complete 1 year of high school. As different study programs lead to different career paths, study program was chosen as the other SEP indicator in this study. Adolescents’ choice of study program has been shown to correlate with their social background [39] and health-related behaviors [34, 40]. Parents’ employment was the other SEP used in this study, as it has been associated with health and health behaviors among adolescents [41].
The general health outcome in this study, body weight (expressed by BMI), was measured. BMI is commonly used as an indicator of body fatness, which is a health risk factor. Indeed, BMI is a ratio between weight and height, and it cannot distinguish between body fatness and fat-free mass [42]. On the other hand, it has been shown that BMI-for-age was a good indicator of body fatness, especially among heavier children and adolescents [43].
The oral health outcome in this study, dental caries experience, was measured and expressed as DMFT score. The DMFT index reflects not only the severity of disease, but also the treatment factor, as filled teeth are included in the score and might be a result of more frequent utilization of dental services [44, 45]. On the other hand, DMFT score is the most commonly used measurement of oral health [46].
Adolescence has been described as a key period for developing health behaviors, thus determining future health. West discussed that it is also a period during which social equality in health is more predominant than inequality, and he suggested that this might be related to the youth culture, secondary school, and school friends that become more important for health equality/inequality than parents’ SEP [47]. Despite the equalizing effect, school creates new inequalities related to study program and/or climate and gender [48]. In our study, the associations between study program, one of the SEP indicators, and body weight; and between study program and dental caries experience, proved to be statistically significant only among girls. This finding is in line with a previous prospective Norwegian cohort study that demonstrated social inequalities in health behaviors among girls based on admission to given study programs [34]. In Norway, the choice of study program has been shown to depend mainly on the occupation of role models, role models for adolescents being mostly their friends and acquaintances, persons from the same social environment [49].
Lower mother’s education, another SEP indicator used in this study, was positively associated with higher BMI only among boys (Table 4). This finding might refer to gender orientation in adolescents’ behavior. It might be that boys are less mature and more dependent on their mothers, as mothers have been shown to be “the prime mover in the health and welfare of the child” [50]. This may also indicate that the Norwegian school system is better adapted to girls’ maturity than to boys’. In addition, social inequalities in BMI were based not only on mother’s education, but also on study program. In addition to the indirect influence, boys reported that their parents’ occupation, which depends on education, influenced their choice of study program [49]. Furthermore, more boys than girls reported to perceive people on TV as role models; thus they were presumably less influenced by their school’s social environment than were girls at this age [49]. Our findings regarding mother’s education and boy’s health is in contrast to a study from the USA, in which father’s health-risk lifestyle, which consisted of diet, physical activity, smoking, alcohol use, and sleep, affected boys’ health-risk behavior, while mother’s behavior affected girls’ behavior; however parents’ health-risk lifestyle was not included in this study [51]. It has been shown in Norway that father’s occupation predicted changes in health behavior among 13-21-year-old girls [34]. We may speculate that father’s occupation is linked to father’s education, but in the present study, father’s education did not have a statistically significant association with outcomes among girls or among boys; thus it was not included in the final statistical models. Given the differences across genders of parents and children, future studies investigating social inequalities in adolescents should address the issue of gender in the relation between parents and their children. Parents’ employment, another SEP indicator, was independently associated with DMFT score among boys. A study in Hungary showed that incomplete parental employment (unemployed, retired, housewife) resulted in inconsistent associations; it was positively associated with health conditions, like depressive and psychosomatic symptoms, but negatively associated with behavioral factors, like smoking, drinking, and drug use among adolescents [41]. As dental caries is a condition that is highly dependent on behavioral factors, it could be argued that the negative effect of parents’ employment on behavioral factors in the Hungarian study is in line with our findings.
Girls enrolled in a sports or physical education program (versus the vocational program) had similar odds for being overweight/obese and having higher dental caries experience when adjusted for the same set of variables (OR 0.20 and OR 0.26, respectively). One may deduce that body weight and dental caries experience are related through common social determinants (in this case SEP indicator, education program) rather than direct oral-general health links; thus supporting the broader concept of social determinants as common risk factors between oral and general health. It must be noted that it is not the study program itself that is a risk factor, but the social context that leads the adolescent to choose a particular program. Body weight and dental caries experience did not produce similar associations with any other SEP indicator used in this study. This may be explained by the fact that adolescence is a relatively healthy period of life, when harmful health behaviors have not yet had time to manifest. In addition, recorded health behaviors and our chosen general health outcome, body weight (expressed by BMI), are prone to change, especially during adolescence, which raises questions about whether a single measurement of these outcomes can depict the real situation over time [52]. On the other hand, boys living without adults had more than two-fold higher odds for being overweight/obese and having high dental caries experience. This finding suggests that not only SEP indicators, but also demographic characteristics, such as household composition, may be a common social determinant for general and oral health conditions among adolescents.