Norwegian 1968.

Methods	Norwegian Vegetable Oil Experiment of 1965‐6 RCT, parallel, 2 arms (ALA linseed oil vs omega 6 sunflower oil), 1 year Risk of bias: moderate or high
Participants	Men working in Norwegian companies aged 50‐59 years N: 6716 intervention, 6690 control Level of risk for CVD: low (working men, though a few had had a previous MI or angina) Men: 100% Mean age in years (SD): unclear Age range: 50‐59 years Smokers: unclear (˜48% non‐smokers) Hypertension: unclear Medications taken by at least 50% of those in the control group: not reported Medications taken by 20%‐49% of those in the control group: not reported Medications taken by some, but less than 20% of the control group: not reported Location: Norway Ethnicity: unclear
Interventions	Type: supplementary food (oil) Comparison: ALA vs omega 6 Intervention: linseed oil, 10 mL/d (55% ALA), 5.5 g/d ALA, 1.5 g/d linoleic. Dose: 5.5 g/d ALA Control: sunflower oil, 10 mL/d (1.4% ALA), 0.1 g/d ALA, 6.3 g/d linoleic. Vitamin E was added to both oils. Compliance: 73% were still taking the linseed oil at 1 year, 72% were still taking their sunflower oil at 1 year (unclear how this was ascertained) Duration of intervention: 12 months
Outcomes	Main study outcome: morbidity and mortality Dropouts: survival status was traced for all but 4 included men, health status was missing for about 80 men in total or 0.6%. Available outcomes: total and CV deaths, MI, angina, stroke, peripheral vascular disease, combined CV events, total cholesterol (subgroup) Response to contact: no
Notes	Study funding: not stated
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Paper states "simple randomisation" without clarification
Allocation concealment (selection bias)	Unclear risk	Few details provided
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Paper states that the workplace doctors who administered the trial locally were sent bottles for each participant marked only with their trial number, and that "appearance and taste of the products were so similar that most participants were unable to identify the type"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Company physicians recorded health status, and were also blinded to intervention (as above)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Detailed description, and those who left employment during the study were followed up for survival and morbidity via the main health system
Selective reporting (reporting bias)	Unclear risk	No protocol or trials registration found
Attention	Low risk	As company physicians administered oils and assessed outcomes but were blind to treatment arm there could not be attention bias
Compliance	Unclear risk	73% were still taking the linseed oil at 1 year, 72% were still taking their sunflower oil at 1 year (unclear how this was ascertained)
Other bias	Low risk	No further bias noted