Background:
Fish consumption has been associated with reduced risk of sudden cardiac death. It has been suggested that the long-chain omega-3 fatty acids from fish are responsible for the beneficial effects of fish consumption. The QT interval on the ECG measures the duration of ventricular repolarization, and a long QT interval is one of the major risk factors for sudden cardiac death. Our goal was to study the association between the serum long-chain omega-3 fatty acids eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) and QT interval duration in middle aged men. As fish is also the major source of methylmercury, an environmental contaminant proposed to have adverse cardiovascular effects, we also evaluated the impact of methylmercury exposure on the QT duration.
Methods:
A total of 1411 men from the population-based Kuopio Ischaemic Heart Disease Risk Factor Study, aged 42–60 years and free of cardiovascular disease, were included. A standardized resting 12-lead ECG was used for recording. Men with QRS ≥120 ms were excluded. The heart rate-corrected QT interval (QTc) was calculated using the Bazett’s formula. Prolonged QTc was defined as QTc >440 ms. Quartiles of the percentage of EPA, DPA and DHA of all serum fatty acids were used as the exposure. Hair mercury in quartiles was used as a marker for methylmercury exposure.
Results:
The mean±SD concentrations were 4.70±1.61% for EPA+DPA+DHA, 1.69±0.92% for EPA, 0.55±0.10% for DPA and 2.46±0.74% for DHA, of all serum fatty acids. The mean QTc interval in the quartiles of serum EPA+DPA+DHA was 417, 417, 415 and 414 ms (P for trend 0.02), after adjustment for age, examination year, smoking, alcohol intake, physical activity, body mass index, education, income, diabetes, treated hypertension and arrhythmia medication. Prolonged QTc was found in 169 of the 1411 men (12%). The multivariate-adjusted odds ratio (OR) for prolonged QTc in the quartiles of EPA+DPA+DHA was 1, 0.90, 0.83 and 0.63 [95% confidence interval (CI) 0.39–1.02, P for trend 0.05]. The OR in the highest vs. the lowest quartile was 0.58 (95% CI 0.36–0.93, P for trend 0.03) for EPA, 0.68 (95% CI 0.43–1.09, P for trend 0.06) for DPA and 0.59 (95% CI 0.35–0.98, P for trend 0.04) for DHA. The mean±SD hair mercury concentration was 1.9±2.0 μg/g. Hair mercury was not associated with QTc, unadjusted or adjusted. The multivariate-adjusted OR for prolonged QTc in the quartiles of hair mercury was 1, 0.97, 0.99 and 1.04 (95% CI 0.64–1.69), P for trend 0.80.
Conclusions:
Increased concentration of long-chain omega-3 fatty acids in serum, a marker of fish or fish oil consumption, appears to protect against prolonged QTc in eastern Finnish middle-aged men. Methylmercury exposure is not associated with QTc in this study population.
Hair mercury levels, dietary intake of omega-3 fatty acids and ovarian reserve among women attending a fertility center