Omega-3 fatty acid prevents heart rate variability reductions associated with particulate matter

Context: Environmental exposure to particulate matter of 2.5 μm or less (PM_2.5) has been associated with changes in heart rate variability (HRV). Objective: To evaluate the effect of supplementation with omega-3 polyunsaturated fatty acids on the reduction of HRV associated with PM _2.5 exposure. Design: Randomized double-blind trial. Setting: Mexico City, Mexico. Participants: 50 nursing home residents older than 60 yr. Intervention: Randomization to either 2 g/d of fish oil versus 2 g/d of soy oil as the control, with 6 mo follow-up (1-mo presupplementation and 5-mo supplementation) or repeated HRV measurements. PM_2.5 was monitored indoors and outdoors. Main Outcome Measure: The association between HRV and 1 SD change in PM_2.5 (8 μg/m³). Results: In the group receiving fish oil, the reduction in HRV-high-frequency log₁₀- transformed associated with a 1-SD change in PM_2.5 was -54% (95% confidence interval, -72, -24) in the presupplementation phase, and only -7% (95% confidence interval, -20, +7) in the supplementation phase (p < 0.01 for the effect of supplementation), with changes in other HRV parameters also being significantly less pronounced during supplementation. Small decreases in PM_2.5-associated reductions in HRV parameters also occurred in the group receiving soy oil, but these were not significant. Fish oil supplementation was significantly better in preventing the reduction in percentage of successive normal RR intervals differing by more than 50 ms (p = 0.03) and the root square of the mean of the sum of the squares of differences between adjacent intervals (p = 0.05) than soy oil supplementation. Interpretation: Supplementation with 2 g/d of fish oil prevented HRV decline related to PM_2.5 exposure in the study population.