Boreham 1999.

Methods	Study design: prospective cohort study. Analysis methods for cohorts: GEE used to investigate the associations between biological CHD risk factors (BMI, sum of skinfolds, SBP, DBP and serum total cholesterol) and lifestyle predictor variables (habitual physical activity, smoking and dietary intake). How were missing data handled? Complete data sets available for 229 boys and 230 girls (89% follow‐up rate for both sexes). Of children lost to follow‐up, reasons were declined to participate (17%), illness (46%), moving school in the interim (31%) or for other reasons (6%). Number of study contacts: 2 (12 and 15 years). Period of follow‐up (total period of observation): 3 years. Periods of recruitment: 1989‐1990. Sample size justification adequately described? Yes. Sample size calculation for the original cross‐sectional survey: target sample of 250 per age/gender group based on variability of pilot study results and represented a 2% random sample of each population group in Northern Ireland. Sampling method: stratified sample. School children selected from 16 schools in Northern Ireland. Within each school, children were randomly selected. Of all children recruited, overall response rate was 78% (1015 children; 506 boys and girls aged 15 years; 509 boys and girls aged 12 years). Study objective: to examine relationships between the longitudinal development of biological risk factors for CHD in tandem with the development of key risk behaviours in a representative adolescent population drawn from a region with a high prevalence of CHD risk. Study population: school children aged 12 years in Northern Ireland.
Participants	Baseline characteristics (reported as 1 overall group) Age (mean in years): 12.5 (SD 0.3). Sex: 50.68% girls. Ethnicity: NR. Education: NR. Income: NR. Pubertal stage: Tanner stage: boys (n = 251) stage I (73%), II (14%), III (8%), IV (2%), V (2%); girls (n = 258) stage I (23%), II (24%), III (25%), IV (8%), V (21%). Parental BMI: NR. Child total energy (kJ): overall (n = 509) 10,487 (SD 3122); boys (n = 251) 11,500 (SD 3200); girls (n = 258) 9500 (SD 2700). Child total fat (%TE): overall (n = 509) 39.8 (SD 4.55); boys (n = 251) 39.8 (SD 4.4); girls (n = 258) 39.8 (SD 4.7). Fat (g): overall (n = 509) 112 (SD 37); boys (n = 251) 123 (SD 39); girls (n = 258) 101 (SD 33). Child total protein: NR. Child total CHO (%TE): overall (n = 509) 52.9 (SD 4.9); boys (n = 251) 52.9 (SD 4.4); girls (n = 258) 52.9 (SD 4.9). Child physical activity: physical activity score (max = 100): overall (n = 509) 28.93 (SD 14.4); boys (n = 251) 34 (SD 14); girls (n = 258) 24 (13). Child physical inactivity or screen time or both: NR. Child CVD risk (excluding fatness): SBP: overall (n = 509) 111.3 (SD 11.91); boys (n = 251) 111 (SD 11.6); girls (n = 258) 111.6 (SD 12.2); DBP: overall 69.42 (SD 9.4); boys 68 (SD 9.5); girls 70.8 (SD 9.1); total cholesterol (mmol/L): overall 4.65 (SD 0.8); boys 4.6 (SD 0.82); girls 4.7 (SD 0.77); HDL‐C: overall 1.39 (SD 0.31); boys 1.4 (SD 0.32); girls 1.38 (SD 0.30); smoking ≥1 cigarette/week: overall 2.4%; boys 3.2%; girls 1.6%; positive family history (median): boys 32.3% (95% CI 26.5 to 38.1); girls 31 (95% CI 25.4 to 36.6). Child body fatness: weight (kg): overall (n = 509) 43.31 (SD 9.23); boys (n = 251) 42.6 (SD 9.4); girls (n = 258) 44 (SD 9); BMI: overall 19.05 (SD 3.21); boys 18.9 (SD 3.4); girls 19.2 (SD 3.0); sum of skinfolds: overall 40.79 (SD 18.55); boys 37.9 (SD 20.6); girls 43.6 (SD 15.8); % body fat: overall 22.54 (SD 5.85); boys 19.3 (SD 5.6); girls 25.7 (SD 4.1). Included criteria: children aged 12 years attending selected schools in Northern Ireland. Excluded criteria: NR. Brief description of participants: children aged 12 years attending post‐primary education in Northern Ireland. Total number completed in cohort study: 459. Total number enrolled in cohort study: 509 (12‐year old children).
Interventions	Description of exposure for cohorts Time span: 3 years. Dietary assessment method used: diet history method with open‐ended interview. Frequency: single dietary history at 12 (baseline) and 15 years. See Table 9; Table 10; Table 11; Table 12; Table 13; Table 14; Table 15; Table 16; Table 17; Table 18 for details of total fat intake exposure per outcome.
Outcomes	HDL‐C HDL‐C (mmol/L).
Identification	Sponsorship source: Northern Ireland Chest, Heart and Stroke Association, British Heart Foundation, Wellcome Trust. Country: Northern Ireland. Setting: post‐primary schools. Comments: Northern Ireland Young Hearts Project. Author's name: C Boreham. Institution: University of Ulster, Jordanstown. Email: NR. Declaration of interests: no. Study ID: Boreham 1999. Type of record: journal article.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Were adequate outcome data for cohorts available? All outcomes	Low risk	Complete data sets available for 229 boys and 230 girls (89% follow‐up rate for both sexes). Of those lost to follow‐up, reasons were: declined to participate (17%); illness (46%), moving school in the interim (31%) or for other reasons (6%).
Was there matching of less‐exposed and more‐exposed participants for prognostic factors associated with outcome or were relevant statistical adjustments done? All outcomes	Low risk	Adjusted for physical activity, pubertal stage, SES but not for parental BMI or ethnicity. Regression analysis stratified for gender.
Did the exposures between groups differ in components other than only total fat? All outcomes	Low risk
Can we be confident in the assessment of outcomes? All outcomes	Unclear risk	Unclear how many skinfold measurements were performed and who performed these. No details provided by authors regarding weight and height measurements.
Can we be confident in the assessment of exposure? All outcomes	Low risk	Repeated assessment of dietary intake. Analysis adjusted for misreporting.
Can we be confident in the assessment of presence or absence of prognostic factors? All outcomes	Low risk	Repeated assessment of physical activity by a 7‐day recall questionnaire. Sexual maturation assessed according to Tanner stage.
Was selection of less‐exposed and more‐exposed groups from the same population? All outcomes	Low risk	All children were participants of the Northern Ireland Young Hearts cohort study.