Trial Oversight

ASCEND was designed and conducted by independent investigators in the Clinical Trial Service Unit at the University of Oxford (the regulatory trial sponsor). The trial methods, patient characteristics, and data analysis plan (including outcome definitions) have been reported previously.18,19 The protocol (available with the full text of this article at NEJM.org) was approved by the North West Multicenter Research Ethics Committee. The trial was funded by the British Heart Foundation. Capsules containing the n−3 fatty acids and matching placebo (along with funding for packaging) were provided by Mylan (and formerly by Solvay and Abbott), and Bayer provided the aspirin and placebo. Mylan, Solvay, and Abbott had nonvoting representation at meetings of the steering committee and provided comments regarding the trial design and draft manuscript but otherwise had no role in data collection or analysis or in the decision to submit the manuscript for publication.

The manuscript was prepared by the writing committee and was reviewed and approved for submission by the steering committee. The first and last members of the writing committee vouch for the completeness and accuracy of the data and analyses, and for the fidelity of the trial to the study protocol and data analysis plan. Requests for data sharing will be handled in line with the data access and sharing policy of the Nuffield Department of Population Health, University of Oxford (available at www.ndph.ox.ac.uk/about/data-access-policy).

Patients

Men and women who were at least 40 years of age (without an upper age limit) were considered eligible if they had received a diagnosis of diabetes mellitus (any type) but did not have evidence of cardiovascular disease. Key exclusion criteria were a clear indication or contraindication for the receipt of n−3 fatty acids or (with respect to the factorial design, reported separately) aspirin or other condition that might limit adherence to at least 5 years of participation in the trial. Patients who reported the over-the-counter receipt of fish oil or n−3 fatty acid supplements were asked to stop them wherever possible, but they remained eligible to participate in the trial, provided that the daily dose was less than 1 g. All the patients provided written informed consent.

Procedures

Using regional diabetes registers or general practice data from around the United Kingdom, we identified potential patients and mailed them a screening questionnaire. Those who returned the questionnaire indicating that they were willing and eligible to participate in the trial entered a prerandomization run-in phase, during which we supplied capsules containing placebo n−3 fatty acid (and placebo aspirin in the separate portion of the trial), informed their family doctor of their potential participation, and sent them a kit to return nonfasting blood and urine samples and to record measures of blood pressure, height, and weight. After this run-in period of 8 to 10 weeks, patients remained eligible if they returned a randomization questionnaire that confirmed their willingness to continue, they still met the eligibility criteria, and they had adhered to the trial regimen.

Using minimized randomization,19 we then assigned eligible patients to receive 1-g capsules containing either 840 mg of marine n−3 fatty acids (460 mg of eicosapentaenoic acid [EPA] and 380 mg of docosahexaenoic acid [DHA]) (fatty acid group) or a matching placebo capsule (olive oil) to be taken once daily. (In the separate portion of the trial, patients were also assigned to receive 100 mg of aspirin or matching placebo once daily.) The patients then were mailed a 6-month supply of the appropriate active or placebo capsules and tablets until the end of the scheduled treatment period or until the patient chose to discontinue taking either the capsules or tablets.

After randomization, we sent follow-up questionnaires to patients every 6 months until the end of the trial. In these questionnaires, we sought information regarding all serious adverse events (including potential trial outcomes), adherence to trial regimens, use of nontrial antiplatelet or anticoagulant therapy, nonserious adverse events resulting in the discontinuation of a trial agent, and any symptomatic bleeding episodes for which the patients sought medical assistance. After a mean follow-up of 2.5 years, we requested blood and urine samples, along with measures of blood pressure and weight, from 1800 randomly selected patients. (Details are provided in the Methods section of Supplementary Appendix 1, available at NEJM.org.)

Outcomes

While recruitment was still ongoing, we modified the original primary outcome to include transient ischemic attack (TIA) in the definition of serious vascular events, a change that was made to increase the statistical power of the trial. Thus, the prespecified primary efficacy outcome was the first serious vascular event, which was defined as a composite of nonfatal myocardial infarction or stroke (excluding confirmed intracranial hemorrhage), TIA, or vascular death excluding intracranial hemorrhage. The secondary efficacy outcome was a composite of any serious vascular event or any arterial revascularization procedure. All reports of possible primary or secondary outcomes were adjudicated centrally by clinicians who were unaware of trial-group assignments in accordance with prespecified definitions. It was prespecified that analyses would be based on all confirmed plus unrefuted reported events (see the Methods section of Supplementary Appendix 1).

Statistical Analysis

The data analysis plan was finalized by the steering committee and published while all the members were still unaware of the trial results according to group assignment (except for a statistician who was aware of trial-group assignments but was not involved in the development of the analysis plan). In addition to revising the definition of serious vascular events to include TIA, the sample size was increased to at least 15,000 patients and the duration of follow-up was extended to at least 7 years to increase the power of the trial.19 (Details are provided in Supplementary Appendix 1.)

On the basis of a rate of serious vascular events of 1.2 to 1.3% per year, as observed in both groups combined after recruitment was complete, we determined that 7.5 years of scheduled treatment and follow-up would provide a power of 90% at an alpha value of less than 0.05 to detect a relative between-group difference of 15%. We used log-rank methods to conduct intention-to-treat comparisons in time-to-event analyses of the first occurrence of each type of event of interest among patients in the two trial groups. A two-tailed P value of less than 0.05 was considered to indicate statistical significance for the primary efficacy outcome.

For secondary and exploratory outcomes, it was prespecified that the combined secondary outcome of a serious vascular event or revascularization would be used for any subgroup analyses. We made allowance for multiple hypothesis testing in the interpretation of secondary and exploratory outcomes, with no formal adjustment to P values. Consequently, the results are reported as point estimates and 95% confidence intervals that have not been adjusted for multiple comparisons, so the intervals should not be used to infer definitive treatment effects within subgroups or for secondary outcomes. Details regarding other secondary and exploratory assessments are provided in the data analysis plan,19 with further details regarding statistical analysis methods provided in Supplementary Appendix 1.