Dietary fish oil inhibits human erythrocyte Mg,NaK-ATPase.

The effects of long-term treatment with a high dose (7.7 g/day) of n-3 polyunsaturated fatty acids (PUFA) were studied for human red blood cells (RBCs). RBCs isolated from healthy subjects treated for 30 and 180 days with n-3 PUFA showed the following modifications: (1) a time dependent modification of membrane fatty acid composition with a concomitant increase in membrane lipid unsaturation; (2) an increase in lipid peroxidation, expressed as malondialdehyde release, induced in vitro by t-butyl hydroperoxide (t-BOOH); (3) a time-dependent decrease in susceptibility to hemolysis, expressed as K+ leakage, induced in vitro by t-BOOH; (4) a time-dependent decrease in total and ouabain-insensitive Mg,NaK-ATPase activity. These results suggest that long term dietary supplementation with high doses of n-3 PUFA significantly modifies RBC structure and function that might lead to harmful side effects.