A systematic review of fish-oil supplements for the prevention and treatment of hypertension

Aims: Fish oils are widely believed to promote cardiovascular health by lowering blood pressure (BP) but the evidence supporting this is not conclusive. We aimed to systematically review existing evidence. Method: We undertook a systematic review of randomized controlled trials and crossover trials that evaluated the effectiveness of fish-oil supplements. We included trials enrolling adults who were given fish-oil supplements with at least 8 weeks' follow up. Effects on systolic and diastolic BP were assessed using meta-analysis. Meta-regression was undertaken to explore the relationship between dose of fish oil and BP outcomes. Results: We included 17 studies, with a total of 1524 participants. We explored the effects of fish-oil supplements in both normotensive and hypertensive participants with BP 140/85 mmHg at least. Meta-analyses were performed using the inverse-variance method. Data from eight studies in hypertensive participants found a statistically significant reduction in systolic and diastolic BP; 2.56 mmHg (95% CI 0.58 to 4.53) and 1.47 mmHg (95% CI 0.41 to 2.53), respectively. Nine studies in normotensive participants showed a non-significant reduction in both systolic and diastolic BP. Meta-regression showed no significant relationship between dose of fish oil and the effect on BP. Conclusion: The small but statistically significant effects of fish-oil supplements in hypertensive participants in this review have important implications for population health and lowering the risk of stroke and ischaemic heart disease. Their modest effects, however, mean that they should not be recommended as an alternative to BP-lowering drugs where guidelines recommend treatment.