CORVALLIS, OREGON. There is ample evidence that fish consumption and fish oil supplementation help protect against heart disease. However, the main components of fish oils, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are highly unsaturated and would therefore be prone to oxidation. This has prompted some researchers to express concern that fish oils might contribute to the lipid peroxidation involved in the development of atherosclerosis.
Researchers at the Oregon State University have released two major studies designed to further explore this concern. The first study involved 15 postmenopausal women who were randomized to supplement with 15 grams/day of sunflower oil, 15 grams/day of safflower oil or 15 grams/day of fish oil (providing 2.0 grams of EPA and 1.4 grams of DHA per day) in a 3-treatment crossover trial. The researchers conclude that there is no evidence that fish oil supplementation increases lipid peroxidation when assessed by measuring the levels of blood plasma malondialdehyde (MDA) and F2-isoprostanes. However, a slight increase in thiobarbituric acid reactive substances (TBARS) was noted in the group who received fish oil supplementation. The researchers believe this to be insignificant and point out that the TBARS test is somewhat unreliable.
The second study involved 46 postmenopausal women who were randomly assigned to receive daily fish oil supplementation (providing 2.5 grams of EPA and 1.8 grams of DHA) combined with 0, 100, 200 or 400 mg of synthetic vitamin E (RRR-alpha-tocopherol acetate). Each of the 5-week treatment periods was followed by a 4-week washout interval in a 4-treatment, 4-period crossover design.
The researchers noted substantial increases in blood plasma levels of EPA (from 0.110 to 0.734 mmol/L) and DHA (from 0.283 to 0.515 mmol/L). They also observed an average drop in triglyceride concentrations of almost 30%. Vitamin E (alpha-tocopherol) levels rose by about 50% after supplementation with 100 mg/day (50 IU) of alpha-tocopherol-acetate and by about 69% after supplementation with 400 mg/day (200 IU). The increase in alpha-tocopherol level was accompanied by a significant decrease in gamma-tocopherol level. The researchers evaluated the effect of supplementation on lipid oxidation (TBARS) and protein oxidation (carbonyl groups). They did not observe any increased protein oxidation, but did find a small but statistically significant increase in TBARS concentration after fish oil supplementation; they dismiss this finding as being likely to be clinically irrelevant. The size of the increase did not change with increased vitamin E intake. The researchers conclude, “If fish oil consumption does not cause an increase in oxidation as measured by protein carbonyls, then an increased intake of vitamin E [during fish oil supplementation] is not necessary.”
Higdon, Jane V., et al. Supplementation of postmenopausal women with fish oil rich in eicosapentaenoic acid and docosahexaenoic acid is not associated with greater in vivo lipid peroxidation compared with oils rich in oleate and linoleate as assessed by plasma malondialdehyde and F2-isoprostanes. American Journal of Clinical Nutrition, Vol. 72, September 2000, pp. 714-22
Wander, Rosemary C. and Du, Shi-Hua. Oxidation of plasma proteins is not increased after supplementation with eicosapentaenoic and docosahexaenoic acids. American Journal of Clinical Nutrition, Vol. 72, September 2000, pp. 731-37