OPAL 2010.

Methods	Older People And n‐3 Long‐chain polyunsaturated fatty acid (OPAL) 2 arm, parallel, RCT, 12 months Summary risk of bias: low
Participants	Healthy cognitively normal adults aged 70‐79 years N: 434 intervention, 433 control (analysed 376 intervention, 372 control) Level of risk for CVD: low Men: 53.4% intervention, 56.6% control Mean age in years (SD): 74.7 (2.5) intervention, 74.6 (2.7) control Age range: 70‐79 years Smokers: not reported Hypertension: 54.9% intervention, 56.9% control Medications taken by at least 50% of those in the control group: not reported Medications taken by 20%‐49%: not reported Medications taken by some, but < 20%: not reported Location: England and Wales Ethnicity: not reported
Interventions	Type: supplement (capsules) Comparison: EPA + DHA vs MUFA Intervention: 2 × 650 mg capsule/d Ocean Nutrition vanilla flavoured soft gelatin capsule (total daily dose of 200 mg EPA and 500 mg DHA). Dose: 0.7 g/d EPA + DHA Control: 2 × 650 mg olive oil capsule identical to intervention Compliance: count returned capsules. Capsules not returned: Intervention ‐ median: 0.95; IQR: 0.82, 1.00 Control ‐ median: 0.95; IQR: 0.81, 1.00 Fasting serum fatty acids, mg/L, mean (SD) EPA: intervention 49.9, (2.7); control 39.1 (3.1) DHA: intervention 95.6 (3.1); control, 70.7 (2.9) α‐linoleic: intervention 21.5 (0.8); control 22.0 (0.9) Length of intervention: 24 months
Outcomes	Main study outcome: delayed onset of cognitive decline Dropouts: control: 78 (8 died, 53 withdrew, 17 discontinued intervention but provided data); intervention: 67 (9 died, 49 withdrew, 9 discontinued intervention but provided data) Available outcomes: deaths, MI, arrhythmias, stroke, diabetes, lipids Response to contact: yes
Notes	Study funding: UK Food Standards Agency, NHS R&D provided support costs
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were "selected in random blocks". "Research nurses telephoned a central computerized randomization service to obtain treatment allocation codes".
Allocation concealment (selection bias)	Low risk	Central allocation via telephone
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Identical capsules (vanilla‐flavoured, dark‐brown coloured). Supplements packaged into identical pots, each containing 180 capsules, labelled by staff not involved in the study. All project staff were unaware of group assignments until after data analysis.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	All project staff were unaware of group assignments until after data analysis.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Participants who discontinued the supplements invited to an interview at 24 months. Dropouts explained and similar in both arms (intervention 49 withdrew, control 53 withdrew)
Selective reporting (reporting bias)	High risk	ISRCTN72331636. Trial registered 2004, before study began. Protocol published 2006. Publication of first results 2010. Many outcomes, such as depression and BP were stated in trials registry entry but not reported.
Attention	Low risk	All participants had the same review schedule, and staff were unaware of assignments
Compliance	Low risk	Count returned capsules. Capsules not returned (intervention ‐ median: 0.95; IQR: 0.82, 1.00; control ‐ median: 0.95; IQR: 0.81, 1.00). Fasting serum fatty acids, mg/L, mean (SD): EPA, intervention 49.9 (2.7); control 39.1 (3.1). DHA, intervention 95.6 (3.1); control 70.7 (2.9). α‐linoleic: intervention 21.5 (0.8); control 22.0 (0.9)
Other bias	Low risk	No further bias noted