Longitudinal Associations Between Childhood Obesity and Academic Achievement: Systematic Review with Focus Group Data

In January 2017, a literature search was performed in Medline, Embase, PsycINFO, Education Resource Information Centre and SportDiscus; this was restricted to English language but not publication year. The search strategy was adapted for each database and is shown for Medline (ovid) in Table 1. Reference lists and forward citations of included studies were screened. Titles and abstracts were screened independently for eligibility (AM, JNB). Full-text articles were independently screened for inclusion by AM, JNB and SM (DHS arbitrated) using the following inclusion criteria:

Experimental studies were excluded as these are systematically reviewed elsewhere [22]; an update of the evidence from experimental studies is currently in progress.

Data were independently extracted by two reviewers and cross-checked using a tested and pre-defined data extraction template. Included studies were independently scored for methodological quality by AM and SM, disagreements were resolved through discussion. Quality assessment was scored using criteria for observational longitudinal research [23]. Quality domains included sampling and recruitment, participant characteristics, attrition, data collection methods, and data (total 19 items). Quality criteria were scored as positive, negative or ‘unclear’. If a study provided no or insufficient information, we scored the criterion at issue as ‘unclear’. Where the study referred to additional publications, we retrieved the publication to score the quality criterion. Studies were considered of high methodological quality when the percentage of items that scored positively was ≥70% [24].

A narrative evidence synthesis was performed for which individual study findings were synthesised graphically by school subjects, type of obesity measure and sex. The primary analysis considered the study quality in that studies with an overall quality score of <70%, and studies with a quality score ≥70% but with self-reported weight and height, and/or academic achievement were removed from the evidence synthesis. Where both objectively and subjectively assessed academic achievement was available, findings of objectively obtained scores were considered for the evidence synthesis. Study and population characteristics and assessment tools for academic achievement varied substantially between included studies. Although several studies utilised similar cohort studies for their analyses, combining effect sizes of the same study population would result in overestimation of the effect size [25]. Therefore, no meta-analysis was performed.

The systematic literature search results were summarised in Fig. 1. Eighty potentially relevant full-text articles were identified, of which 30 articles (31 studies) were included in this review.

A detailed description of population characteristics, exposure, outcomes, confounding/mediating variables and main results of the included studies is provided in Table 2. The included studies comprised 17 distinct cohort datasets, of which 11/31 studies performed secondary analysis of the Early Childhood Longitudinal Study—Kindergarten Class (ECLS-K) in the USA [26‐36]. Seven studies used five other datasets from the USA [35, 37‐42], and eight studies utilised existing cohort datasets from Canada [43, 44], the UK [45, 46], The Netherlands [47, 48], Australia [49], and Taiwan [50]. Five studies from Australia, Germany, Taiwan, Thailand, and Peru used primary data for their prospective analyses [51‐54]. The number of participants ranged from 405 to 21,260 (median 3362 participants) and the follow-up periods ranged from 1 to 9 years (median 3 years). Twenty-four studies assessed the association between overweight and/or obesity and academic achievement whereas two studies related percentage body fat [46, 53], one study BMI z scores [32] and two studies BMI [40, 54], to children’s academic achievement. Measures of academic achievement were obtained from school records or standardised tests by 25 studies and five studies relied on teacher or self-reported academic attainment [37, 42, 44, 52, 55].

Sixteen studies assessed the association between overweight or obesity at one time point and academic achievement later in life (Fig. 2a). Of those, eight studies were excluded from the primary analysis due to methodological shortcomings (Fig. 2b). Fourteen studies using data from eight cohorts assessed the association between change in obesity status and academic achievement (Fig. 2b). However, only four studies (two cohorts) were of high methodological quality and so included in the primary analysis (Fig. 2a). Change in obesity status was classified as persistent obesity, development of obesity, and ‘growing out’ of obesity (change from obesity to overweight or healthy weight).

All included studies adjusted for a number of confounding variables known to be associated with both obesity and academic achievement such as measures of socioeconomic status (e.g. parental education, family income). The quality scoring of each individual study ranged from 53% [26] to 95% [30, 45]. The level of agreement for the quality scoring between the reviewers (AM, SM) was 96% (k = 0.91). In 24/30 studies, methodological quality was scored high (≥70%).

Figures 2a, and b shows the graphically synthesised data of the included studies on the association between child and adolescent overweight and obesity and academic achievement, namely reading/language, maths, science and a combined average of school subjects. Table 1 also summarises the results for each of the included studies.

The present systematic literature review and data synthesis of high-quality studies indicated that the association between childhood obesity and academic achievement varied by sex, age and school subject. A significantly negative association between obesity and maths achievemement was evident in adolescent girls, while the evidence suggested no association with math achievement in younger girls with obesity and in boys with obesity in general.

Out of the 30 included studies, six studies performed mediation analyses to identify the role of plausible factors that potentially mediate the relationship between child/adolescent obesity and academic achievement. The following mediating factors were assessed:

Following completion of a weight management programme (Get Going NHS Lothian: www.​nhslothian.​scot.​nhs.​uk/​getgoing/​) in Scotland, four obese adolescent girls (aged 12–15 years, mean body mass index 99.6th percentile relative to 1990 UK reference) and one of their respective parent/guardians (i.e. 4 dyads in total) participated in separate focus groups of 60 to 90 min (i.e. two focus groups). Focus groups were led by AM, included semi-structured open-ended questions and were audio recorded and subsequently transcribed verbatim using NVivo10 [56]. Data from adolescents and parents/guardians were analysed separately following an inductive thematic analysis [57]. The text was coded and similar codes were clustered into hierarchical themes. Trustworthiness of the analysis was enhanced through independent coding (AM, AN) and member checking. This study was approved by the University of Edinburgh and the National Health Service South East Scotland Research Ethics Committee.

From the focus groups, it was evident that, despite negative body weight-related experiences in school, the girls had a generally positive attitude to education and school. They said that they do very well in school and usually outperform healthy-weight classmates. The only subject the girls mentioned that they were not good at was Physical Education (PE) and this was perceived to be related to the girls’ body weight. Parents/guardians and adolescents perceived that academic achievement is not necessarily related to body weight per se; academic achievement depends on pupils’ attitude towards learning and efforts put into school work. However, both adolescents and parents/guardians believed that the reason for the girls’ good academic achievement is that they were less distracted from school work due to the lack of friends and absence of good peer relationships. The girls said that having friends in class can lead to girls spending more time talking to their friends rather than concentrating and taking school seriously.

Additional themes emerged on female adolescents’ experiences in the school environment that were directly influenced by their body weight status. Both adolescent girls and parents/guardians reported negative psychological consequences of obesity, for example, low self-confidence and unhappiness due to body weight. Social consequences were also highlighted, for example, the girls reported difficulties being accepted and understood by healthy-weight peers in school, and were felt to be lacking friends. From both adolescents’ and parents/guardians’ responses, it emerged that the girls experienced rejection by peers in school, negative body weight-related comments, classmates laughing and gossiping about them and that at times they feel isolated and ignored. The girls viewed having a higher body weight than other teenagers in school as a disadvantage during PE, and for getting appropriately sized clothes for school (lab coats, school uniform, PE kits). PE was reported to be an environment where the girls were strongly exposed to body weight-related teasing. Some girls also felt ignored and excluded from activities by PE teachers. In contrast, classroom teachers were perceived as non-judgmental towards the increased body weight. Eating healthily in school and receiving support from classmates to do so was described as difficult and sometimes even a reason for being isolated from peers.

Strengths of this work include the use of rigorous systematic review methodology and a focus on longitudinal data to provide a more nuanced insight into the association between obesity and academic achievement. The ability to distinguish between obesity and overweight as exposure variables was also a strength. Adding focus group data provided useful preliminary insight into the perceptions of adolescent girls with obesity and their parents to complement and advance the observational literature.

However, some limitations are notable. Included studies were in English language only; thus, we might have missed relevant studies published in non-English language. Focus group findings are limited in their generalisability given the low number of participants (saturation of themes potentially not reached) and the fact that all those who participated had recently completed a weight management programme (non-participation and non-completion might influence perceptions).

The current evidence on the association between obesity and maths attainment is available primarily from North American and European cohorts and entirely from high-income countries. Further research is needed to establish if an obesity-related deficit in academic achievement is evident in children and adolescents from middle-low-income countries. Given the current steep rise in the prevalence of childhood obesity in these countries [1], if there is an association between obesity and academic achievement in these contexts, the subsequent economic impact of obesity-related deficits may have even more implications for economic growth of middle-low-income countries and for human capital. Prospective cohort studies indicated that adolescent obesity is negatively associated with years of schooling [76, 77], school completion [78], enrolment in higher education [79, 80], income [76, 77, 81] and employment status [82]. The economic argument for the implementation of effective childhood obesity prevention and treatment programmes could therefore be substantial.

The current evidence is also limited on the impact of mediating factors. None of the included longitudinal studies evaluated the mediating effects of sleep deprivation, physical activity levels, type of physical activity, diet/nutritional status and co-morbidities, despite the literature suggesting an important role of these factors in the causal pathway between childhood obesity and academic achievement [12, 13, 15‐17, 83]. However, most recently (after our literature search was performed), new findings were published on the link between meeting lifestyle-behaviour recommendations at age 11 years and academic achievement at age 12 years (n = 4253). Researchers concluded that overweight or obesity was not associated with maths or reading achievement expectation but academic achievement was associated with meeting dietary, sleep and screen time recommendations [84]. Future longitudinal studies should include mediation analysis of those factors to contribute to understanding the underlying mechanisms of a negative association between adolescent obesity and academic achievement. This in turn will help to identify the most promising intervention strategy for promoting educational outcomes. In addition, the ability to identify a factor as a mediator depends on the reliability and validity of the measure and so researchers should avoid utilising crude measurement methods.

Academic achievement might be influenced by a teacher-bias towards obesity, in that children and adolescents are perceived as having poorer reasoning, social, physical and cooperation skills which impact on academic achievement [10, 11, 33, 85•]. However, the empirical evidence is inconsistent [42, 44, 48, 52]; thus, further research to provide empirical tests of this perspective is warranted. Nonetheless, there is convincing evidence on limited educational opportunities when PE teachers hold a biased perception about the abilities of children with obesity [86‐88]. Our focus group data also indicated that during PE, the girls felt ignored and not supported by the teachers. This finding highlights the importance of promoting positive PE experiences among adolescent girls with obesity and indicate a potential role for physical literacy programmes in schools. Whitehead (2010) [89] placed special emphasis on physical literacy being defined by competence-based and interest-based motivation in PE [89]. Chen (2015) recently suggested that a physically literate person should be characterised by self-regulated motivation for physical activity [90]. For adolescents with obesity, the PE experiences should be educational, including learning the values and benefits of physical activity for health and quality of life for sustained participation in physical activity. Regular aerobic physical activity, as part of the school curriculum or extracurricular, was shown to benefit children’s and adolescents’ cognition and academic achievement [18, 91]. Children and adolescents with obesity seem to be even more responsive to physical activity programmes for improved cognitive abilities and academic achievement [22, 92•]. This demands PE teachers more to fully understand the complexity of motivation processes in order to deliver positive PE experiences for adolescents with obesity. Furthermore, school-wide policy action is needed to address weight-based teasing/bullying.