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RESEARCH REPORTS |
1 Institute of Education, University of London, London, UK
2 Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK
3 Department of Social Medicine, University of Bristol, Bristol, UK
Correspondence to:
Ms A Sorhaindo, Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, WC1E 7HT London, UK; annik.sorhaindo{at}lshtm.ac.uk
Accepted for publication 23 November 2007
 | ABSTRACT |
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Design: Using longitudinal data available in the Avon Longitudinal Study of Parents and Children (ALSPAC), multivariate linear regression was used to assess the relative importance of diet at different ages for school attainment.
Main outcome measures: Three indicators of school attainment were used: at ages 4–5 entry assessments to school, at ages 6–7 Key Stage 1 national tests and at ages 10–11 Key Stage 2 national tests. These outcome variables were measured in levels as well as in changes from the previous educational stage.
Results: The key finding at age 3 was that "junk food" dietary pattern had a negative association with the level of school attainment. A weak association remained after controlling for the impact of other dietary patterns at age 3, dietary patterns at ages 4 and 7 and other confounding factors. The authors did not find evidence that eating packed lunches or eating school meals affected children’s attainment, once the impact of junk food dietary pattern at age 3 was accounted for in the model.
Conclusions: Early eating patterns have implications for attainment that appear to persist over time, regardless of subsequent changes in diet.
This issue has had a high profile in the UK partly as a result of the Jamie’s School Dinners television programme originally broadcast in 2005. The programme raised awareness about the poor nutritional content of school meals and children’s preference for foods that are high in energy, fat, sugar and salt. Celebrity chef Jamie Oliver worked with staff and students in UK schools to improve the nutritional content of school meals and began a national campaign to highlight the importance of nutrition for children’s well-being and to improve the nutritional quality of food offered in schools.5 The UK government increased funding for school meals and instituted an agency to advise schools on nutritional standards.6 Staff in schools that managed to improve the nutritional content of their meals reported improvements in students’ behaviour in the classroom that they felt was related to the change in diet.7
Via their effects on cognition, behaviour and physical health, the foods children eat have the potential to impact upon engagement in school and consequent attainment. Previous research on breakfast has focused on the short-term effects of nutrition on cognition and behaviour for children.8–10 There is also evidence that early diet affects children’s ability to think and perform in the long term.11–13 This suggests that appropriate early childhood diets can be important for subsequent school outcomes. However, we are unaware of any studies linking early nutrition specifically to later school attainment.
This paper addresses two research questions. First, what is the relative importance of early diet versus later diet in predicting school attainment? Second, spurred by the recent debate about the role of schools in determining what children eat and research showing that, on average, the nutritional content of school meals is superior to that of packed lunches, we ask: does school attainment differ between children who eat packed lunches and children who eat school meals, conditioned on their pre-school dietary patterns?14
| METHODS |
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Outcome variable: school attainment
In the UK, each member country (England, Wales, Scotland and Northern Ireland) sets standards for what children should be taught at particular ages or Key Stage (KS). Children are then assessed for their attainment of the set curricula at each age or stage. KS scores obtained from the relevant education authorities in the National Pupil Database (NPD) were matched to the ALSPAC data. We used the Key Stage 2 (KS2) results for English, maths and science, administered when children are 10–11 years old, to assess school attainment.
In ALSPAC, some data on KS scores are missing because the NPD does not cover children in private schools (4.3% of pupils); matching was based on the child’s name, date of birth and current postcode, so perfect matching was not always achieved; children initially included in ALSPAC who subsequently moved outside of England were not covered by the NPD. We do not know the proportion of pupils missing because of the last two explanations.
We used KS1 assessments of reading, writing, and maths, administered when the children were 6–7 years old, and on entry assessment in maths, reading, language, and writing, administered by schools and set by local education authorities when the children were 4–5 years old to measure attainment prior to KS2. This allowed for investigation of the impact of dietary patterns on attainment at different ages and on the change in school attainment. Entry assessments were not national or compulsory during the period of data collection so information was available for only two-thirds of the children.
Dietary data
Mothers, or main female carers, completed food frequency questionnaires (FFQs) about their child’s consumption of foods and beverages when the child was 38 months (about 3 years old), 54 months (about 4 years old) and 81 months (about 7 years old). Of the 13 988 children in ALSPAC, dietary information at all three ages was only available for 7703 children (55%).
At 81 months, mothers reported whether their child ate meals served at school or packed lunches provided from home and the frequency with which they did each, recorded as either rarely, once in 2 weeks, once a week, two to four times a week or 5 days a week. Of these children, 29 per cent ate school dinners 5 days a week and nearly half (46%) ate packed lunches 5 days a week.
Of the 7703 children for whom dietary information was collected, 74 per cent had information on both KS2 and KS1 scores. The final study sample consisted of 5741 children with complete information on food frequencies and both school attainment scores results (41%).
Socioeconomic, demographic and lifestyle confounders
As both diet and achievement are influenced by a number of socioeconomic, demographic and lifestyle factors, such factors were controlled for in the analysis to attempt to remove confounding bias. These variables related to measurements taken prior to, or at the time of, the food intake, that is at ages 3–4 and before our measurements of school attainment. For all these variables, we included a missing category to avoid further loss of data.
Relevant sociodemographic information about the child included whether the child was a singleton or multiple birth, their gender and ethnicity, birth weight and the number of siblings at birth. Information on the mother included whether she felt she had difficulties affording food, her employment status, whether she had a partner, her highest educational qualifications at the time of birth, her socioeconomic group (SEG) (defined as professional for SEG I, managerial and technical for SEG II, skilled manual and non-manual for SEG III, partly skilled for SEG IV and unskilled for SEG V), whether she smoked during her pregnancy, whether she was a vegetarian when the child was born and her age at delivery.
Other variables included mother’s parenting, breastfeeding, the household weekly income, housing tenure, whether the child watched children’s television programmes and the HOME score, an indicator of the cognitive stimulation and emotional warmth in the home environment.16
Table 1 lists the frequencies of the confounding variables used in this analysis, comparing those in our sample with the whole cohort. Overall, differences between the means are fairly small. The study sample contains more white male children, more children who watched television, more mothers from the middle socioeconomic group SEG (III), fewer mothers from the lowest SEG (IV or V), more mothers with secondary educational qualifications, fewer mothers with educational qualifications below secondary level and fewer mothers who smoked during pregnancy.
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A score was created for each child by multiplying the factor loadings by the corresponding standardised value for each food and summing across the food types for each of the three dietary patterns. The score has a mean of 0 and a higher score indicates closer association to that dietary pattern.19 An indicator variable was also generated to differentiate between children who ate school dinners 5 days a week, those having packed lunches 5 days a week and those having a combination of packed lunches and school meals.
FA was also performed on the individual KS2 assessments to obtain an overall score with loadings of 0.79 for English, 0.86 for maths and 0.89 for science. Overall scores were also obtained for KS1 and entry assessments. Factor loadings for KS1 were 0.88 for reading, 0.87 for writing and 0.74 for maths, and for entry assessments 0.79 for reading, 0.70 for writing, and 0.70 for maths. The resulting scores had a mean of 0 and standard deviation of 1, thus a higher score indicates a higher result on overall tests.
Multivariate linear regression was used to assess the relative importance of diet at different ages for school attainment, allowing for the cluster of multiple births. The dependent variables, attainment score at different ages, were regressed against the dietary pattern scores, controlling for observable confounding factors. In this way, we assessed the relative importance of dietary patterns at different ages in predicting school attainment at different ages. The first model estimated the impact of dietary patterns at ages 3 and 4 on entry assessments (age 4–5) controlling for socioeconomic and demographic variables. The second model estimated, separately, the impact of dietary patterns at ages 3, 4 and 7 on KS1 and KS2 results, controlling for all confounding variables. The final two models estimated the impact of dietary patterns on KS1 controlling for entry assessments, and on KS2 controlling for KS1 attainment, both including all confounding variables. Models 1 and 2 estimate the impact of dietary patterns on the level of attainment, whereas the final model estimates this impact on the change in attainment.
Finally, we investigated the differences in KS2 attainment between children who ate packed lunches and those who ate school meals, controlling for KS1 test scores, food intake prior to school entry (age 3) and other relevant socioeconomic and demographic factors. In this estimation, we focused on the importance of the estimated parameter of packed lunches relative to school meals.
| RESULTS |
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In subgroup analysis, we found a negative socioeconomic gradient for the relationship between "junk food" dietary pattern and school attainment, but only between those in the highest SEG and the rest of the population. The estimated effect for the highest socioeconomic group was the lowest (–0.021); the effect for the middle socioeconomic group was –0.046 and finally the effect for the lowest socioeconomic group was –0.043. However, we found no evidence that SEG moderated the relationship between dietary patterns and attainment.
School meals or packed lunches and KS2 results
We found no difference in the average increase of KS2 scores between children who ate packed lunches 5 days a week and children who ate school meals 5 days a week or children who ate school meals 5 days a week and children who had some combination of packed lunches and school meals during the school week (table 4). This result was robust to the inclusion of prior attainment and consumption of "junk food" at age 3, differentiating for a free school meal indicator (column 1) and to the inclusion of other confounding variables (column 2).
| DISCUSSION |
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Although there was a negative association between early "junk food" consumption and later attainment scores, the estimated effect was small, suggesting that nutrition may have a diminishing role in attainment as children grow older, when the effect is more likely to be mediated by prior attainment. This may indicate a developmental period or stage where children are more susceptible to the long-term cognitive impact of poor nutrition. There is potential for a stronger effect as this sample is slightly biased towards more educated, middle class, and health-conscious mothers, though there was no evidence that socioeconomic status of the family mediated this relationship.
There was no relationship between school meals or packed lunch consumption and later attainment once the "junk food" dietary pattern prior to school entry and other confounding factors were introduced in the analysis. This suggests that although the emphasis on school meals is valuable and important, it must be part of a wider concern with nutrition more generally, in homes, in packed lunches and in school meals.
Full data were available on only 41 per cent of the original cohort and there were fewer ethnic minorities and disadvantaged families in this group than in the original cohort. Therefore, it was important to take account of these variables in the statistical models used. With a longitudinal research design, it is possible to account for some of the confounding bias in the relationship between dietary patterns and school attainment. For instance, mothers’ health beliefs, educational attitudes and parenting behaviours may impact upon the provision of healthy food at home and provision of an educational environment, thus confounding the relationship.21 In as much as we have information about the mother, via the HOME score and other measures, we can condition out some of the confounding bias. Still, results from this paper do not prove causality.
We used FA to reduce KS results on maths, science and English into a single variable related to school attainment. We also relied on the dietary patterns identified using FA.17 18 This method for obtaining dietary patterns has been criticised for its subjectivity in identifying the underlying patterns.22 It has also been argued that FA is population specific, and, as such, the results reported here may not be replicated in other studies. Despite this, previous research with different populations has linked diet and aspects of school performance.11
This study has extended this area of research by linking children’s diet before entry into formal education with outcomes for later school attainment. This highlights a challenge for policy-makers in establishing the location of responsibility for school outcomes related to aspects of health. The recent debate in the UK on school dinners has placed the onus on government agencies responsible for education to respond to the health needs of children to improve their educational outcomes. But if educational outcomes in part depend on nutritional intake before the start of school, with whom does responsibility lie? At what stage are interventions most effective? Is money best spent on school dinners or on the provision of health information to new mothers? This further supports movements towards collaborative efforts between agencies, but highlights the challenge of designing policy when the outcomes of one agency rely upon the inputs of another.23 Improving the nutritional intake of children in the UK calls for a concerted effort between schools, families, government departments and other agencies to improve diets inside and out of school.
What this study adds
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Policy implications This research highlights the importance of diet before entry into formal education for later school attainment and calls for a concerted effort between schools, families, government departments and other agencies to improve the nutritional intake of children.
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| APPENDIX |
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| ACKNOWLEDGMENTS |
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Author contributions: Leon Feinstein, Ricardo Sabates and Annik Sorhaindo carried out the analysis of the data and wrote the first draft of the paper. David Herrick compiled the school assessment data, Pauline Emmett and Imogen Rogers designed and led the dietary data collection within ALSPAC, Kate Northstone produced the dietary patterns scores from the original ALSPAC questionnaires. All authors were responsible for critical revisions and final approval of the manuscript.
| FOOTNOTES |
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Table A1 is published online only at http://jech.bmj.com/content/vol62/issue8 Competing interests: All authors declare that they had no financial or personal interest with the funding agency or any other agency related to the topic of this article.
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