The Impact of Long-term School-based Physical Activity Interventions on Body Mass Index of Primary School Children

A Meta-analysis of Randomized Controlled Trials

Hong Mei; Yuelin Xiong; Shuixian Xie; Siyu Guo; Yukun Li; Bingbing Guo; Jianduan Zhang


BMC Public Health. 2016;16(205) 

In This Article


Literature Eligibility

There were 11,175 potentially relevant articles identified according to the search protocol, and another 156 articles were manually retrieved from the reference lists of relevant meta-analysis and systematic reviews. With duplicates of records searched in both search protocol and manually retrieved, there was 11,158 left. Of those, 10,751 studies were excluded for being non-obesity prevention studies (10,203 records), non-English (225 records), and without available outcome measures (323 records). An additional 389 studies were excluded due to the following reasons: non-school-based studies (76 records), not from primary school (95 records), non-RCT (87 records), no BMI outcome available (46 records), and intervention duration <12 months (85 records). As a result, 18 eligible studies were retained for the meta-analysis. The flow chart is shown in Fig. 1.

Figure 1.

Flow Diagram of article research

Characteristics of Included Studies

The 18 studies were published from 1999 to 2014, with a total of 22,381 children included. Two of the included articles were from the same research project (one presented the medium term effect and one showed the final term effect).[37,38] Nine studies were conducted in Europe,[33,39–46] 5 studies were from the United States,[34,47–50] 4 studies were conducted in Africa[37,38] and Asia[51,52] (2 each). Among the 18 studies, 7 studies (38.9 %) included more than 1000 children; 3 (16.7 %) studies have only recruited roughly 100 children, the rest ranged from 346 to 646 children. Most of the included studies targeted both genders with a gender ratio (boy to girl) that ranged from 0.79 to 1.18; while only one targeted boys. Five interventions (27.8 %) lasted less than two years, and 8 of them (44.2 %) continued for at least three years. The majority of the studies (14, 77.8 %) were cluster RCT, and the reminding 4 (22.2 %) studies were RCTs. Five studies (27.8 %) only included PA intervention and the rest 13 (72.2 %) involved both PA and nutrition components. For the measurement method of PA, 11 studies (61.1 %) only used questionnaires, 5 (27.8 %) adopted electronic instruments, and 2 study (11.1 %) used both questionnaires and electronic instruments. There were 8 studies that indicated PA intensity indicators. Both Mackelvie et al.[39] and Ahamed et al.[43] used the scores from Physical Activity Questionnaires (PAQ-C) for Children to assess PA intensity, while only Ahamed et al.[43] stressed the PAQ-C scores for both baseline and terminal line. The other two studies from Manios et al.[33] and Angelopoulos et al.[41] used the same PA intervention and same questionnaire to assess the moderate-to-vigorous PA (MVPA). While the former one shown significant effect of MVPA intervention on reducing BMI increment, the latter one shown nonsignificant results. There were 4 studies that used electronic instruments to assess PA intensity. The instruments differed between these studies (Caballero et al.[47] used the Tritrac R3D, Hemokinetics, Iowa City; Donnelly et al.[48] used Actigraph, 7163, Pensacola, FL; Dzewaltowski et al.[50] used Actigrap GT1M accelerometers, Shalimar, FL; Kriemler et al.[40] used MTI/CSA 7164, Actigraph, Shalimar, FL). There were 12 studies conducted with the PA intervention time ≤100 min/week and 6 studies with PA intervention time ranged from 120–450 min/week. Details can be seen in Table 1.

Quality of the Studies

Two investigators individually assessed the quality of 18 studies using the Jadad Scale and yielded almost identical JSSs, i.e., only 6 items were scoring differently out of 126 items. A third investigator reexamined the eligible studies on each item especially the 6 inconsistent items, and then the final JSS were given to each study. Five studies received scores of 3, 12 studies attained scores of 2, and the remaining one received 1 score. No significant difference in quality was found between RCTs and cluster RCTs by the Chi-square test. Results were presented in Table 2.

Primary Outcome

Children's ΔBMI was significantly different (p < 0.05) between the PA intervention group and the control group (SMD: -2.23 kg/m2, 90 % CI: -2.92, -1.56) (Fig. 2). High heterogeneity (I 2 = 99.8 %) was identified cross the studies. The Begg's Funnel plot was asymmetric with some outliers (p < 0.05) (Fig. 3).

Figure 2.

The forest plot for the 18 studies by publishing year. The filled triangles and diamonds represent the SMD and 90 % confidence interval for each study with a default weight percentage. The diamond with hollow refers to the overall SMD and 90 % CI, along with the vertical dashed line as centerline of the average SMD for the 18 studies. Random effect was used for the analysis

Figure 3.

The funnel plot for the 18 studies. The horizontal axis is the coefficient of SMD for BMI change in intervention groups and control groups, and vertical axis (s.e.of: SMD) is the reciprocal of SMD for BMI change in intervention groups and control groups. Random effect was used for the analysis

Sensitivity and Stratified Analysis

The meta-influence plot showed 7 studies (from Jiang et al.,[52] Tarro et al.,[46] Angelopoulos et al.,[41] Manios et al.,[33] Llargues et al.,[38] Lohman et al.,[49] and Magnusson et al.[42]) have significant impacts on the overall effect. When these studies were removed from the analysis, the difference of ΔBMI between the intervention group and the control group increased from -2.23 kg/m2 to -2.00 kg/m2 (90 % CI: -0.30, -0.09). Simultaneously, the heterogeneity among the remaining studies was reduced (I 2 = 90.5 %).

With the seven studies excluded, stratified analysis showed that intervention type (PA and PA&N) did affect the summary estimate of ΔBMI. The difference of ΔBMI for PA group and control group was -0.13 (N = 5, 90 % CI: -0.29, 0.04; I 2 = 89.8 %); while ΔBMI between PA&N group and control group was -0.26 kg/m2 (N = 6, 90 % CI: -0.30, -0.09; I 2 = 92.1 %). The SMD for studies with the weekly PA time ranged from 36–100 min was -0.22 (90 % CI: -0.38, -0.05, I 2 = 94.0 %), and for weekly PA interventions >100 min, the SMD was -0.18 (90 % CI: -0.35, 0.00; I 2 = 87.1 %). Overall intervention duration of studies also impacted the BMI change. The difference of ΔBMI was significantly different between the interventions that lasted for 12–24 months groups and control groups (SMD: -0.20 kg/m2, 90 % CI: -0.39, -0.02); and the difference of ΔBMI in intervention lasted for over two years and the control group was -0.19 kg/m2 (90 % CI: -0.35, -0.03).

Stratified analysis specific to the study area, design, and quality showed no significant difference in BMI changes between different groups. No group difference was found for PA measurement (p > 0.05).