Associations Between Plasma Omega-3 and Fish Oil Use With Risk of Atrial Fibrillation in the UK Biobank.

Plasma omega-3 levels were inversely associated with incident atrial fibrillation.

• HR per interquintile range (IQ5R) was 0.89 (95% CI, 0.86–0.93)
• Analysis included a random sample of 261,108 participants without prevalent AF who had data on plasma omega-3 levels
• Median follow-up was 12.7 years
• Multivariable-adjusted hazard ratios were computed both continuously (per IQ5R) and by quintile

After multivariable adjustment including age as a continuous variable, fish oil supplement use was not associated with incident atrial fibrillation risk.

• HR for fish oil supplement use was 1.00 (95% CI, 0.97–1.02)
• 466,169 participants reported about fish oil supplement use
• Fish oil supplement use was reported by 31% of the cohort
• Fish oil supplement use was more common in older individuals
• A prior report had treated age as a dichotomous rather than continuous variable, which the authors identified as a methodological distinction

Fish oil supplement use was more prevalent among older individuals in the UK Biobank cohort.

• 31% of the cohort reported fish oil supplement use
• Age distribution differed between fish oil supplement users and non-users
• This age imbalance was identified as a potential confounding factor in earlier analyses that treated age as a dichotomous variable

Meta-analyses of randomized trials with omega-3 products had previously found an increased risk of atrial fibrillation, in contrast to biomarker-based analyses.

• A prior meta-analysis based on blood levels of omega-3 fatty acids found an inverse relationship with AF risk
• A recent UK Biobank study had concluded that fish oil supplement use was associated with increased risk of AF
• The discrepancy between supplement-use studies and blood-level studies motivated the present analysis examining both measures simultaneously

The study was a retrospective analysis of UK Biobank data linking both plasma omega-3 levels and self-reported fish oil supplement use to incident atrial fibrillation.

• Only participants without prevalent AF at baseline were included
• A random sample of 261,108 participants had plasma omega-3 data and 466,169 reported fish oil supplement use
• The primary outcome was incident AF during follow-up with a median of 12.7 years
• Multivariable-adjusted hazard ratios were computed for fatty acids continuously per IQ5R and by quintile, and for dichotomous versus continuous fish oil supplement use