Dietary fish oil supplementation and regular physical activity can improve outcomes in patients with established CVD. Exercise has been shown to improve heart rate variability (HRV), a predictor of cardiac death, but whether fish oil benefits HRV is controversial. Obese adults at risk of future coronary disease have impaired HRV and may benefit from these interventions. We evaluated the effect of DHA-rich tuna fish oil supplementation with and without regular exercise on HRV in sedentary, overweight adults with risk factors for coronary disease. In a randomised, double-blind, parallel comparison, sixty-five volunteers consumed 6 g fish oil/d (DHA 1·56 g/d, EPA 0·36 g/d) or sunflower-seed oil (placebo) for 12 weeks. Half of each oil group also undertook regular moderate physical activity (3 d/week for 45 min, at 75 % of age-predicted maximal heart rate (HR)). Resting HR and the HR response to submaximal exercise were measured at weeks 0, 6 and 12. In forty-six subjects, HRV was also assessed by power spectrum analysis of 20 min electrocardiogram recordings taken supine at baseline and 12 weeks. Fish oil supplementation improved HRV by increasing high-frequency power, representing parasympathetic activity, compared with placebo (P = 0·01; oil ×  time interaction). It also reduced HR at rest and during submaximal exercise (P = 0·008; oil ×  time interaction). There were no significant fish oil ×  exercise interactions. Dietary supplementation with DHA-rich fish oil reduced HR and modulated HRV in keeping with an improved parasympathetic–sympathetic balance in overweight adults with risk factors for future coronary disease.

CHD mortality is extremely low in Japan, particularly in rural districts, when compared with that in Western countries. This has been partly attributed to the difference in dietary lifestyle. We investigated the factors influencing CHD mortality in a rural coastal district of Japan, comprising mercantile, farming, and fishing areas with distinct dietary habits. We prospectively examined the incidence of CHD from 1994 to 1998, as well as coronary risk factors and serum fatty acid concentrations. The incidence of angina pectoris was significantly (P=0·01) lower in the fishing area than in the mercantile and farming areas. Blood pressure, physical activity, prevalence of diabetes, serum levels of uric acid and HDL-cholesterol were similar between the three areas. Total- and LDL-cholesterol levels were significantly lower but the smoking rate was markedly higher in the fishing area than in the other two areas. Serum levels of saturated fatty acids and n−6 polyunsaturated fatty acids (PUFA) were lowest in the fishing area, but n−3 PUFA did not differ significantly. The n−6:n−3 PUFA ratio was lowest and eicosapentaenoic:arachidonic acid was highest in the fishing area. Although many previous studies have emphasized the beneficial effect of n−3 PUFA in preventing CHD, the present study indicated that a lower intake of n−6 PUFA and saturated fatty acids has an additional preventive effect on CHD even when the serum level of n−3 PUFA is high because of high dietary fish consumption.

Nine healthy male subjects consumed a daily fish oil supplement providing 2.1 g docosahexaenoic acid (22:6 n-3; DHA) and 0.8 g eicosapentaenoic acid (20:5 n-3; EPA) for 6 weeks. The proportion of EPA and DHA in plasma, erythrocytes, leucocytes and platelet phospholipids was increased by the supplement. Plasma concentration of triacylglycerol and very-low-density-lipoprotein-cholesterol were lowered and those of high-density-lipotrotein (HDL)- and HDL2-cholesterol and apoprotein B were increased. Platelet aggregation and thromboxane B2 production induced by collagen were partially inhibited. Both systolic and diastolic blood pressure fell during treatment and rose following withdrawal of the supplement. Statistically significant reductions in erythrocyte counts, packed cell volume and haemoglobin and increases in total leucocyte and monocyte counts occurred with the supplement. Plasma α-tocopherol concentrations fell below the normal range during the period of supplementation. It is suggested that future studies consider components other than EPA in fish oil. Further studies are needed to investigate the extent to which fish oil increases the requirement for antioxidant nutrients.