After one month of taking high-dose fish oil, your red blood cells temporarily get more of a protective antioxidant called alpha-tocopherol, which helps them resist damage from oxidation.

After six months of high-dose fish oil, the protective antioxidant in red blood cells drops back down, and the cells become more easily damaged by oxidation — and the higher the dose, the worse it gets.

People who take the highest dose of fish oil for six months end up with more oxidized fat in their red blood cells than those taking a low dose — even if they started with the same level of protection.