JAMA MARCH 16, 2021

Effect of Marine Omega-3 Fatty Acid and Vitamin D Supplementation on Incident Atrial Fibrillation: A Randomized Clinical Trial

Christine M. Albert, Nancy R. Cook, Julie E. Buring, et al.

Bottom Line

In this large-scale randomized trial, neither daily supplementation with marine omega-3 fatty acids (840 mg) nor vitamin D3 (2000 IU) significantly reduced the incidence of atrial fibrillation over a median follow-up of 5.3 years in a primary prevention population.

Key Findings

1. Marine omega-3 fatty acid supplementation did not reduce incident atrial fibrillation compared to placebo (469 events [3.7%] vs. 431 events [3.4%]; hazard ratio [HR], 1.09; 95% CI, 0.96-1.24; P = 0.19).

2. Vitamin D3 supplementation did not reduce incident atrial fibrillation compared to placebo (469 events [3.7%] vs. 431 events [3.4%]; hazard ratio [HR], 1.09; 95% CI, 0.96-1.25; P = 0.19).

3. No significant interaction was observed between the two study agents (P = 0.39), and findings were consistent across secondary endpoints including paroxysmal and non-paroxysmal atrial fibrillation subtypes.

Study Design

Design

RCT

Double-Blind

Sample

25,119

Patients

Duration

5.3 yr

Median

Setting

United States

Population Men aged 50 years or older and women aged 55 years or older with no history of cardiovascular disease, cancer, or atrial fibrillation at baseline.

Intervention Daily supplementation with 2000 IU of vitamin D3 and/or 840 mg of marine omega-3 fatty acids (460 mg EPA and 380 mg DHA).

Comparator Matching placebo.

Outcome Incident atrial fibrillation, ascertained by participant self-report and validated by medical record review.

Study Limitations

• The study relied on participant self-report and medical record linkage to ascertain atrial fibrillation, which may have led to an underestimation of asymptomatic or undiagnosed cases.

• The population was limited to individuals without a history of cardiovascular disease, cancer, or AF, potentially limiting the generalizability of the findings to higher-risk cohorts.

• The dosage of marine omega-3 fatty acids used (840 mg) was lower than doses typically tested in trials where potential pro-arrhythmic signals have been observed, limiting the ability to definitively address risks associated with higher doses.

Clinical Significance

The VITAL-Rhythm trial provides definitive evidence that daily supplementation with standard doses of vitamin D3 or marine omega-3 fatty acids does not provide a protective benefit for the primary prevention of atrial fibrillation in a general, healthy population. These results suggest that such supplements should not be recommended for the specific purpose of preventing new-onset atrial fibrillation.

Historical Context

Observational studies and smaller, mixed-result trials previously suggested that marine omega-3 fatty acids and vitamin D might influence atrial remodeling and AF risk. This trial served as a landmark primary prevention study, embedded within the larger VITAL study, designed to provide robust, randomized data to resolve lingering uncertainty regarding the preventive utility of these widely consumed dietary supplements.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

What are the proposed biological mechanisms by which omega-3 fatty acids and vitamin D were hypothesized to reduce the risk of atrial fibrillation (AF) prior to the VITAL-Rhythm trial?

Key Response

Omega-3 fatty acids are thought to incorporate into cardiomyocyte membranes, potentially modulating ion channel function (sodium and L-type calcium channels) to produce anti-arrhythmic effects and reducing systemic inflammation. Vitamin D is hypothesized to inhibit the renin-angiotensin-aldosterone system and reduce atrial structural remodeling and fibrosis, both of which are foundational to the pathogenesis of AF.

Resident

In a primary prevention setting, if a patient with hypertension and obesity asks if taking 1 gram of fish oil daily will prevent 'the irregular heartbeat' they heard about in the news, how should you counsel them based on the VITAL-Rhythm results?

Key Response

The resident should counsel the patient that according to a large-scale randomized trial (VITAL-Rhythm), daily supplementation with 840 mg of omega-3 fatty acids did not reduce the risk of developing AF over a 5-year period. Management should instead focus on established risk factor modifications such as weight loss and blood pressure control, which have stronger evidence for AF prevention.

Fellow

Contrast the neutral AF findings of the VITAL-Rhythm trial (840 mg/d omega-3) with the results of the REDUCE-IT and STRENGTH trials. What does this suggest about the dose-response relationship between omega-3 intake and atrial arrhythmia risk?

Key Response

While VITAL-Rhythm showed a neutral effect at a lower dose (approx. 1g/day), higher-dose trials (4g/day) like REDUCE-IT and STRENGTH actually demonstrated an increased risk of incident AF. This suggests a potential dose-dependent 'pro-arrhythmic' effect at high doses, whereas lower doses appear safe but ineffective for primary prevention.

Attending

Given the results of VITAL-Rhythm and subsequent meta-analyses of omega-3 trials, how should clinicians reconcile the cardiovascular benefits of omega-3s (e.g., triglyceride lowering, MACE reduction in specific groups) with the apparent lack of benefit—or potential harm—regarding atrial fibrillation?

Key Response

This requires a nuanced shared decision-making approach. While low-dose omega-3s are neutral for AF, the cardiologist must weigh the specific CV benefits seen in trials like REDUCE-IT against the statistically significant increase in AF risk at high doses, particularly in patients with pre-existing atrial substrates or multiple risk factors for arrhythmia.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

The VITAL-Rhythm trial utilized a 2x2 factorial design. What are the specific methodological advantages of this design in the context of AF research, and what are the primary statistical risks regarding 'interaction' between the two interventions?

Key Response

Factorial designs allow for the simultaneous testing of two independent hypotheses (Vitamin D and Omega-3) in the same population, increasing efficiency. However, the validity of the results depends on the assumption of 'no interaction'—the idea that the effect of one intervention is the same regardless of the presence of the other. If a synergistic or antagonistic interaction exists and is not powered for or modeled correctly, it can lead to misleading conclusions about the individual interventions.

Journal Editor

From a peer-review perspective, how does the baseline 'healthy' status and the primary prevention nature of the VITAL cohort influence the interpretation of the null results, and could this be viewed as a type II error?

Key Response

A reviewer would flag that the event rate in a primary prevention cohort is inherently lower than in high-risk populations. While the sample size was large (n=25,119), if the effect size of these supplements is very small or only manifests in specific high-risk subsets (e.g., post-CABG or those with severe deficiency), the trial might be underpowered to detect a difference, though the 95% confidence intervals in VITAL are narrow enough to rule out any large clinical benefit.

Guideline Committee

Based on the VITAL-Rhythm findings, should current AF guidelines (like those from the AHA/ACC/HRS) be updated to include a specific recommendation regarding the use of fish oil or Vitamin D for primary prevention?

Key Response

The findings support a Class III (No Benefit) recommendation for the use of Vitamin D and low-dose marine omega-3s for the primary prevention of AF. Current guidelines (e.g., 2023 ACC/AHA/ACCP/HRS) focus heavily on Class I recommendations for lifestyle and risk factor modification (obesity, HTN, alcohol) for AF prevention; VITAL provides high-quality Level A evidence that these supplements do not contribute to these prevention goals.

Clinical Landscape

Noteworthy Related Trials

2019

REDUCE-IT Trial

n = 8,179 · NEJM

Tested

Icosapent ethyl 4g daily

Population

Patients with elevated triglycerides and established CVD or diabetes

Comparator

Placebo

Endpoint

Composite of cardiovascular death, MI, stroke, coronary revascularization, or unstable angina

Key result: Icosapent ethyl significantly reduced the risk of ischemic events compared to placebo. However, it was associated with an increased incidence of atrial fibrillation.

2020

STRENGTH Trial

n = 13,078 · JAMA

Tested

Epanova (carboxylic acid EPA and DHA)

Population

Patients with high CV risk, hypertriglyceridemia, and low HDL cholesterol

Comparator

Corn oil

Endpoint

Composite of CV death, MI, stroke, coronary revascularization, or unstable angina

Key result: The trial was terminated early for futility as the intervention did not reduce major adverse cardiovascular events and showed a trend toward increased atrial fibrillation.

2021

OMEMI Trial

n = 1,027 · Circulation

Tested

1.8g n-3 polyunsaturated fatty acids daily

Population

Elderly patients with recent myocardial infarction

Comparator

Corn oil

Endpoint

Composite of nonfatal MI, unplanned revascularization, stroke, all-cause mortality, or heart failure hospitalization

Key result: Supplementation did not reduce clinical events in elderly post-MI patients and appeared to potentially increase the risk of atrial fibrillation.

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