Effect of omega-3 fatty acid supplementation on blood pressure and heart rate variability following sympathoexcitatory stress in mild hypertensive and normotensive subjects.

Elliott Carthy1,2, Leigh White1, Fraser Russell1,4, Mark Holmes1,4, Anthony Leicht3, Peter Brooks1,4, Philip Barker1, Deborah Hitchen-Holmes1, Chris Askew1,41Faculty of Science, Health, Education & Engineering, University of the Sunshine Coast, QLD, Australia, 2School of , Imperial College London, London, UK, 3Institute of Sport and Exercise Science, James Cook University, QLD, Australia, 4USC Inflammation and Healing Research Cluster, University of the Sunshine Coast, QLD, Australia

Background: Long chain omega-3 polyunsaturated fatty acids (n-3 FA) have known anti-hypertensive effects; however their mechanism of action remains unclear [Cicero et al., 2010; Cicero et al., 2009]. Resting hypertension has been associated with autonomic dysfunction, namely an increase in sympathetic and/or a decrease in parasympathetic activity at rest [Schroeder et al., 2003]. We hypothesised that n-3 FAs supplementation would increase vagal modulations and/or decrease sympathetic activity, contributing to their anti-hypertensive effects.

Methods: Mild hypertensive (HT: mean±SEM; blood pressure: 142.4±2.19/81.1±2.91mmHg; age: 51.5±2.94years; body mass index: 30.3±1.25kg/m2; n=16) and normotensive participants (NT: mean±SEM; blood pressure: 116.2±1.56/73.0±1.07mmHg; age: 50.5±1.49years; body mass index: 25.8±0.59kg/m2; n=42) were supplemented with 2.52g/day of n-3 FA (docosahexaenoic acid: 0.84g; eicosapentaenoic acid: 1.68g; Omega Heart, Blackmores Pty Ltd.) or placebo (canola oil; Blackmores Pty Ltd.) for nine weeks. Participants were included if they were 30-85 years, on a low fish diet and not taking fish oil capsules or anti-hypertensive medication. Participants provided 4 repeat morning measurements of resting BP, with readings 2-4 used for analysis. Subjects underwent an assessment of their resting heart rate variability (HRV) and BP initially, and at 3 weekly intervals. The omega-3 index was measured using gas chromatography-mass spectrometry. This study received approval from the University of the Sunshine Coast Human Research Ethics Committee (EC00297 A/08/167).

Results: There was a significant increase in the omega-3 index for the n-3 FA supplemented group (Before: 5.43±0.18%; After: 8.31±0.30%; p<0.05) compared to the placebo group (Before: 5.67±0.24%; After: 5.50±0.23%). A non-significant trend for reduction in systolic (SBP), diastolic (DBP) and mean arterial pressure (MAP) was observed for n-3 FA supplemented HT and NT participants when compared to placebo (SBP: -2.67±1.04 vs. -0.69±1.17mmHg; p=0.21; DBP: -1.68±0.82 vs. -0.71±0.89mmHg; p=0.43; MAP: -1.91±0.83 vs. -0.18±1.02mmHg; p=0.19). There were no significant main treatment effects for the HT or NT groups considering HRV throughout the intervention.

Conclusions: The significant increase in omega-3 index for the n-3 FA supplemented group confirmed incorporation of n-3 FA into red blood cell membrane phospholipids. The magnitude of this response was consistent with current recommendations for cardioprotection (>8.0%) [Harris, 2010]. There was a tendency for a greater overall reduction in BP in participants who were supplemented with n-3 FA, irrespective of their basal BP. However, this was not significant, and not associated with changes in HRV, forearm blood flow or reactive hyperemia in those supplemented with n-3 FA compared to placebo. The current results indicate that n-3 FA supplementation at a level needed for cardioprotection was not beneficial at reducing BP or altering autonomic function for mild HT and NT participants. It remains unclear whether supplementation with n-3 FA may be more effective (i.e. improve cardiac autonomic function) for those with a more severe hypertensive state or in in higher dosage.

References

Cicero AFG et al, Clinical and Experimental Hypertension 32:137, 2010

Cicero AFG et al, Current Vascular Pharmacology 7:330, 2009

Harris WS, Current Cardiology Reports 12:503, 2010

Schroeder EB et al, Hypertension 42:1106, 2003