11. SI!

Cardiovascular diseases (CVD) are a leading cause of death, comprising approximately half of all non-communicable disease (NCD) deaths (Benziger, Roth and Moran, 2016[1]). One of the primary determinants of CVD is obesity, as well as its associated comorbidities (diabetes, hypertension) (Rodríguez-Artalejo et al., 2002[2]). In 2018, almost 60% of people in OECD countries were overweight, and 25% were obese (OECD, 2019[3]). The adoption of unhealthy behaviours leading to the development of CVD risk factors takes place in early childhood (Peñalvo et al., 2013[4]). However, obesity is largely preventable, highlighting the importance of effective health promotion early on in the life course.

The SI! intervention is a school-based multidimensional health intervention in Madrid, Spain, targeting cardiovascular health. It seeks to equip schoolchildren with the behaviours and skills necessary to maintain healthy life habits throughout the life course. The intervention focuses on diet, physical activity (PA), body and heart, and emotional management. The 2011 trial in Madrid studied in this analysis1 included children aged three, four and five years of age and also involved families, teachers and schooling environments. The intervention is delivered over a four-week period every year and is dedicated to teaching children, parents and children about the importance of leading a healthy lifestyle (112 hours in total, 70 of which are dedicated to children) (Peñalvo et al., 2013[4]). On a broader level, the intervention helps promote healthier school and home environments, by working with the canteens, for instance, to design nutritionally adequate menus, or by recommending healthy snacks to the children’s families (20 hours) (Peñalvo et al., 2013[4]).

Twenty-four schools in Madrid participated in the 2011 study, with half the schools completing the intervention and the other half being assigned to the control group. The aim of the intervention was to have a positive effect on the schoolchildren’s lifestyle behaviours, as well as on adiposity markers.

This section analyses SI! against the five criteria within OECD’s Best Practice Identification Framework – Effectiveness, Efficiency, Equity, Evidence-base and Extent of coverage (see Box 11.1 for a high level assessment of SI!). Further details on the OECD Framework can be found in in Annex A.

The results of the SI! Intervention show that the intervention was generally successful in positively impacting the schoolchildren’s knowledge, attitude and habits (KAH) relating to the intervention content across all age groups (Peñalvo et al., 2015[5]). Indeed, all three years had higher overall KAH scores than the control group at every follow-up check. The greatest improvements were seen in terms of physical activity, where the KAH was consistently higher in every age group (Peñalvo et al., 2015[5]). At the one-year follow-up for instance, knowledge, attitudes and habits regarding physical activity were higher in the intervention group than the control by 1.41, 2.10 and 2.52 in KAH scores from baseline for children aged three, four and five years, respectively (Table 11.2). There were also marginal improvements for the dietary component across all years, however, some participants aged four and five showed no difference in KAH scores. Despite the overall positive impact of the intervention, there were little to no changes in terms of the KAH scores relating to body and heart, further, they were not statistically significant (Peñalvo et al., 2015[5]). Further, data was not available in year two for those aged five and in year three for those aged four or five.

The SI! intervention had marginal effects on adiposity markers, but these were more significant than the results of similar studies. Due to the duration of the trial, the greatest overall change in anthropometric measurements was seen for those aged three years. There were no significant differences observed in either the one-year (five years of age) or the two-year (four years of age) groups. The waist circumference was in fact lower for the control than the intervention group at the three year follow-up, but this result was not statistically significant (p = 0.179) (Peñalvo et al., 2015[5]). Nonetheless, 1.1% of children in the intervention group were considered obese and 7% overweight by the end of the intervention, versus 1.3% and 7.4% in the control group, respectively (Peñalvo et al., 2015[5]). The effects in terms of BMI and subscapular skinfold (to assess body fat) were minimal, but the results were still favourable towards the intervention group throughout (Peñalvo et al., 2015[5]). Finally, the z-score (the median value of the reference population) for tricep skinfold and waist circumference was more likely to decline by at least 0.1 in the intervention group2 (Peñalvo et al., 2015[5]).

The results of this trial are more significant than those of comparable studies. Very few interventions of two years duration or less have had any positive impact on children’s anthropometric measurements (Peñalvo et al., 2015[5]). The Healthy Study in the United States, a similar three-year multidimensional intervention targeting childhood obesity in 11-year-olds, for instance, did not alter the incidence or prevalence of obesity in either the intervention or control group, nor the remission of overweight or obesity (Foster et al., 2008[6]). Similarly, the CATCH study, a comparable three-year multifaceted intervention targeting children’s cardiovascular health also in the United States, did not record successful outcomes in terms of cholesterol measures, blood pressure or body size (Luepker, 1996[7]). Finally, the ToyBox-study, a school-based intervention seeking to prevent childhood obesity in six European countries did not have any significant impact on the prevalence of obesity or overweight amongst the participants (Miguel-Berges et al., 2019[8]). However, the study did nonetheless lead to an increase in physical activity amongst Belgian schoolchildren (De Craemer et al., 2014[9]). These results point to the potential of the SI! intervention and the importance of long-term comprehensive health promotion interventions early in life.

The OECD’s 2019 obesity report highlights that the investment in school-based interventions corresponds approximately to its GDP benefit, and that annual savings in health expenditure for this type of intervention across all countries could amount to USD PPP 37 million (EUR 25 million) (OECD, 2019[3]). Moreover, the average yearly cost per capita for school-based interventions in Spain is USD PPP 3.05 (EUR 2.09), and these interventions could save USD PPP 0.18 (EUR 0.12) per capita in health expenditure annually.

It is possible that the SI! intervention is cost-effective given that it is comparable to other cost-effective school-based childhood obesity interventions. According to the Join Action on Nutrition and Physical Activity (JANPA), the SI! intervention’s overall budget was under EUR 50 000 per year. No additional data on the cost-effectiveness of the intervention was available. However, comparable multicomponent school-based obesity prevention interventions were generally found to be cost-effective or even cost-saving (Zanganeh et al., 2019[10]). A school-based nutrition and PA intervention including children and their parents in Germany, for example, achieved costs of EUR 11.11 (USD PPP 16.24) for each centimetre reduction in waist circumference (Kesztyüs et al., 2011[11]). The overall intervention generally presented favourable cost-effectiveness ratios (Kesztyüs et al., 2011[11]). Finally, a comprehensive PA intervention in schools in Australia reached cost-effectiveness ratios of AUD 1 408 (USD PPP 978) per BMI unit avoided and AUD 563 (USD PPP 391) per 10% reduction in BMI z-score (Sutherland et al., 2016[12]).

The SI! intervention can be said to focus on people living in conditions of disadvantage. Indeed, it was specific in selecting the schools in the intervention according to socio-economic criteria. These stipulated that 10-32% of the schoolchildren had to be from an immigrant background, 36-54% had to be receiving free or subsidised school meals and 13-20% had to be receiving free school books and materials.

However, the results showed that the variations in overall KAH score were related to parental socio-economic variables (p for interaction < 0.05). Children whose parents had at least a high school diploma had a higher KAH score on average (p for interaction < 0.001) (Peñalvo et al., 2015[5]). This was also the case for children whose parents earned more than the minimum annual wage in Spain (p for interaction < 0.001) and who were of European origin (p < 0.001) (Peñalvo et al., 2015[5]). No significant variations were observed according to parental age.

The trial of the SI! intervention was set up as a cluster-RCT open label intervention (where information is not withheld from trial participants). These types of studies are generally preferable as the randomisation element reduces the possibility of bias. The selected 24 schools were allocated on a random basis to the intervention or control group. Moreover, the schools were randomised on a stratified basis by immigration and scholarship percentage in order to guarantee an overall cultural and socio-economic balance amongst the groups (Peñalvo et al., 2015[5]).

Using the Quality Assessment Tool for Quantitative Studies, the design of the study to evaluate SI! was rated as “strong” in several areas: selection, bias, study design, confounders and data collection methods (Effective Public Health Practice Project, 1998[13]). However, similar to many public health interventions, neither researchers nor participants were blinded therefore the study was rated as “weak” against this section. Details of the assessment are in Table 11.3.

Information on participation rates is not publically available and has therefore not been possible to assess. However, if scaled-up to a national level, this type of intervention has the potential to cover a large part of the target population. Indeed, it focuses on children who are of age to be in compulsory education, and in EU27 and OECD countries, in general, school participation rates are virtually universal.

The design of SI! fits many of the overarching success factors in terms of school-based childhood obesity prevention interventions (Box 11.2). The trial was a multidimensional intervention aimed at generating long-term lifestyle behaviour change amongst schoolchildren. It provided training and support for teachers, parental activities and promoted healthy diet and PA behaviours within schools by positively impacting the school community. Moreover, the content of the intervention was integrated into the curriculum to minimise the burden on schools.

Literature on best practices in this field emphasise the importance of changes within the school. In upscaling or adapting this intervention, consideration could be given to monitoring the food environment, in order to enhance effectiveness. Other policies for intervention administrators to consider include further regulation and improvement of the nutritional quality of foods onsite (e.g. school meals, vending machines, children’s packed lunches). Additional emphasis could also be placed on exercise within schools (e.g. by integrating additional obligatory and voluntary PA sessions throughout the school week). A school-based intervention in Australia, for instance, integrated PA activities into the school framework, which resulted in significantly more moderate-intensity and vigorous-intensity PA (MVPA) amongst the children (27 min more MVPA per week) (Sutherland et al., 2015[20]), and an average decline in BMI by –0.28 kg  at 24 months (Hollis et al., 2016[21]). Finally, in line with WHO’s Nutrition-Friendly Schools Initiative (NFSI), SI! administrators should continue (WHO, 2021[22]):

  • Focusing on increasing parental involvement, for example by promoting face-to-face interaction

  • Engaging the community, for example, by procuring healthy fruit and vegetables from local suppliers (in line with EU’s Farm to Fork Strategy)

  • To ensure that teachers receive appropriate training and education to deliver obesity prevention activities.

Policy makers and programme administrators should prioritise an efficiency study of SI! given this information isn’t currently available. Example efficiency indicators include incremental cost effectiveness ratios using BMI units avoided, reduction in waist circumference (in centimetres) and/or reduction in BMI z-scores as outcomes of interest. For example, ToyBox – another school-based obesity prevention case study (see Chapter 8) – assessed efficiency using incremental cost-effectiveness ratios, specifically the cost per quality-adjusted life year gained.

A review of publically available information indicates the SI! Intervention is implemented homogenously. To enhance equity, to the extent possible, SI! administrators are encouraged to undertake a review to determine whether the intervention should be adapted to meet the needs of different vulnerable groups.

In order to better understand how different groups of students benefit from the intervention, future evaluations should break down key indicators, for example, by family SES and ethnicity. A richer dataset will ultimately enhance the evidence-base and allow administrators to adapt the intervention to better meet the needs of disadvantaged students.

Future evaluations would benefit from including additional diet-related outcome indicators such as fruit and vegetable consumption (e.g. the proportion of children who consume fruits/vegetables at least once per day).

Information on participation rates are not publically available, nevertheless, high-level policies to boost participation rates in school-based activities are summarised below:

  • Promoting the intervention with support from government organisations to enhance trust amongst parents. For example, the Good for Kids, Good for Life intervention in New South Wales (Australia) was promoted using a support letter from the State’s Chief Health Officer. Policy makers however should first consider if messaging from government organisations may in fact reduce uptake among disadvantaged groups. For example, there is evidence showing those with a low SES and/or lower level of education are more anxious and suspicious of prevention messaging from public health authorities (Peretti-Watel and Constance, 2009[23]).

  • Promoting SI! as a healthy behaviour intervention that aims to boost enjoyable physical activity and healthy eating as opposed to obesity prevention. Framing SI! in a positive light may reduce stigma associated with participation.

  • Increasing efforts to recruit students whose parents are from culturally or linguistically diverse backgrounds given consent may be harder to obtain (for example, by including staff members who are knowledgeable about relevant cultural characteristics).

  • Promoting the intervention over a sufficiently long time period using colourful, “eye-grabbing” material in conjunction with frequent digital and face-to-face follow-up with parents.

This section explores the transferability of SI! is broken into three components: 1) an examination of previous transfers; 2) a transferability assessment using publically available data; and 3) additional considerations for policy makers interested in transferring SI!.

SI! has not been transferred outside of Spain, however, school-based interventions targeting obesity are common across OECD and non-OECD European countries.

The following section outlines the methodological framework to assess transferability and results from the assessment.

Details on the methodological framework to assess transferability can be found in Annex A.

Several indicators to assess the transferability of SI! were identified (Table 11.4). Please note, the assessment is intentionally high level given the availability of public data covering OECD and non-OECD European countries.

Data from publically available sources indicate SI! is transferable based on data related to the economic, sector (i.e. early childhood education) and political contexts (Table 11.5). For example, SI! is likely to have political support given most governments have set out a national strategy addressing childhood obesity. Further, spending on early childhood education and care (ECEC) is higher, on average, amongst OECD and non-OECD EU countries compared to Spain (USD PPP 9 729 versus USD PPP 7 759). However, SI! may have a lower extent of coverage in other countries given enrolment rates in ECEC are relatively high in Spain (97% versus 83%, on average, amongst OECD and non-OECD EU countries).

To help consolidate findings from the transferability assessment above, countries have been clustered into one of three groups, based on indicators reported in Table 11.4. Countries in clusters with more positive values have the greatest transfer potential. For further details on the methodological approach used, please refer to Annex A.

Key findings from each of the clusters are below with further details in Figure 11.1 and Table 11.6:

  • Countries in cluster one have political, economic and sector specific arrangements in place to transfer SI!. Countries in this cluster are therefore less likely to experience issues associated with implementing and operating SI! in their local context.

  • Countries in cluster two have political and sector specific arrangements in place to transfer this intervention indicating they are also good transfer candidates. However, before transferring the intervention, countries in this cluster would benefit from increasing spending on early childhood education and care (ECEC) to ensure long-term affordability. It is important to note that Spain, which operates SI!, falls under this cluster indicating high levels of ECEC spending, although ideal, is not a pre-requisite.

  • Remaining countries are in cluster three, which before transferring SI! would benefit from undertaking further analysis to ensure the intervention is affordable and aligns with overarching political priorities.

Data from publically available datasets is not ideal to assess the transferability of SI!, for example, the level of parental engagement in schools. Therefore, Box 11.3 outlines several new indicators policy makers should consider before transferring SI!.

Over the course of the past three decades, there has been a significant increase in the prevalence of overweight and obesity worldwide. The adoption of inadequate lifestyle behaviours leading to situations of obesity or overweight takes place in early childhood (Peñalvo et al., 2013[27]). The SI! Intervention aims to prevent such habits from forming through a school-based multicomponent intervention.

The results from the study show that intervention has been successful in positively impacting schoolchildren’s healthy lifestyle knowledge, attitude and habits, notably in terms of physical activity, but also in terms of diet. The intervention also achieved reductions in anthropometric measurements in the children, even though these were at times minimal. Although data surrounding cost was not available, comparable interventions have been shown to be cost-effective, and even cost-saving. The quality of evidence used to evaluate the intervention can be considered to be of moderate quality. Furthermore, the coverage of the intervention in its entirety is relatively extensive (children aged 3-16), but its scope was perhaps limited in the initial trial by its focus on children aged 3-5 in the Madrid area. Moreover, the SI! intervention was specific in selecting intervention and control schools according to socio-economic criteria, although the results from the trial highlighted a need to focus more on these variables in the design of the intervention. Finally, the study fit the majority of best practice criteria for obesity prevention interventions in schools, however, further changes, such as incorporating physical activity, could be considered to achieve the intervention’s core objective: reducing obesity and improving overall health among school-aged children.

Based on available information, SI! is considered broadly transferable. For example, the SI! intervention addresses obesity amongst children, which is a top public health priority across a range of OECD and European countries. However, prior to implementation, policy makers in the target setting should collect information on other important indicators, including those outlined in Box 11.4.


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← 1. The SI! intervention in its entirety includes schoolchildren aged 3-16. However, this study focuses exclusively on the pilot trial of the intervention implemented in 2011 amongst children 3-5 years of age, given the lack of available information on other age groups.

← 2. Z-scores reflect the number of standard deviations away from the mean in the reference group (i.e. a z-score of -1 indicates the score is 1 standard deviation below the men).

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