Fish oil increases peripheral capillary blood cell velocity in humans.

Fish oils containing n-3 fatty acids have been shown in humans to decrease platelet aggregation in vitro, lower plasma triglycerides, and to increase bleeding time. The in vivo effects of fish oils on microcirculatory blood flow in humans has not been studied to date. Twenty-one male subjects were randomly assigned to either olive oil (n = 10) or fish oil (n = 11) supplemented groups to determine the effects of these oils on capillary blood flow velocity (CBV) in the nailfold area. The subjects were given the oils for three weeks (1.5 g oil/10 kg b.wt./day) in a single blind study design. In addition to CBV plasma lipid profiles, blood viscosity, blood pressure and platelet and erythrocyte fatty acids were also determined prior to and after the dietary intervention. Fish oil supplementation significantly increased CBV, by 1.75-fold (0.144 +/- 0.069 to 0.253 +/- 0.147 mm/s). The olive oil group remained unchanged. Increased levels of n-3 fatty acids were noted in platelets and erythrocytes of the fish compared to olive oil-supplemented groups. Blood viscosity was unaltered in both groups, however, blood pressure in the olive oil supplemented group was significantly decreased. Plasma triglycerides were significantly decreased in the fish oil supplemented group. These observations suggest that increases in CBV after fish oil supplementation are due to changes in vascular tone and not to alterations in blood pressure or blood viscosity.