School-related sedentary behaviours and indicators of health and well-being among children and youth: a systematic review

Table 2 Summary of results for biomarker indicators organized by study design

No. of participants (No. of studies)	Design	Risk of bias	Inconsistency	Indirectness	Imprecision	Other	Absolute effect	Quality
525 (2) [49, 51]	Clustered RCT	Serious risk of bias^a	No serious risk of inconsistency	No serious risk of indirectness	No serious risk of imprecision	None	Overall: • 2/2 studies reported null findings Additional PA: • 1/1 study reported null findings [49] Recess/PE: • 1/1 study reported null findings [51]	Moderate
41 (1) [54]	Non-Randomised Intervention	Serious risk of bias^b	No serious risk of inconsistency	No serious risk of indirectness	Very serious risk of imprecision^c	None	Standing desk: • 1/1 study reported null findings [54]	Very Low
698 (1) [76]	Longitudinal	Serious risk of bias^d	No serious risk of inconsistency	No serious risk of indirectness	Serious risk of imprecision^e	None	Homework: • 1/1 study reported null findings [76]	Very Low

Mean age at baseline ranged from 6.7 to 11.5 years; when mean age was not reported one study had an age range of 11 to 12 years, while another study sampled from children in grades 1 and 5. Study designs included clustered RCT, non-randomised interventions, and longitudinal with up to 5 years follow-up. Biomarkers were assessed objectively by blood pressure (systolic, diastolic, and mean arterial blood pressures), fasting blood draws (glucose, insulin, high-density lipoprotein-cholesterol (HDL), low-density lipoprotein-cholesterol (LDL) and triglycerides) and composite cardiovascular risk scores (z-scores of waist circumference, blood pressure [mean of systolic and diastolic blood pressure z-scores], glucose, inverted HDL, and triglycerides)
^a1/2 studies had intervention and control groups in the same school
^b 1/1 study had intervention and control group in the same school
^c Only one study, with a small sample size
^d Differences in measurement of blood pressure from baseline to follow-up
^e Only one study, but large sample size

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