An interesting new study found that fresh fish oil supplements are better at reducing low density lipoprotein (LDL), intermediate density lipoprotein (IDL), phospholipids, cholesteryl ester and unesterified cholesterol bound to LDL and IDL than sunflower oil or stale fish oil supplements.
The omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in oily fish, such as salmon, sardines, mackerel, and herring are thought to lower blood triacylglyceride (TAG) levels and blood pressure platelet aggregation, as well as prevent arrhythmias. However, the effects of these fatty acids on cholesterol levels is not completely clear, with conflicting results between studies. These contradictory results could be, in part, due to fish oil supplements undergoing varying degrees of oxidation over time.
Both EPA and DHA are prone to oxidation, which results in the formation of peroxides. Oxidation not only reduces the efficacy of fish oil supplements but the aldehydes that are formed as a result can have a range of adverse effects. Studies in animals show that exposure to oxidized omega-3 PUFAs over the long-term may lead to growth retardation, increased inflammation, cardiomyopathy and carcinogenesis. Given the popularity of fish oil supplements, it is imperative that studies be conducted to examine the efficacy and adverse effects of oxidized or rancid fish oil supplements on human health.
A study recently published in the British Journal of Medicine attempted to address questions about the efficacy of fresh and oxidized fish oil supplements by assessing blood levels of the different types of cholesterol and TAGs. A total of 54 healthy men and women aged 18–50 years were included in the study. Individuals who were pregnant, lactating, had hypertension (≥160/100 mmHg), fasting levels of total cholesterol >7·5 mΜ, TAG > 4·0 mmol/l, glucose >6·0 mmol/l, C-reactive protein >10 mg/l, BMI ≥ 30 kg/m2, abnormal levels of thyroxine stimulating hormone (TSH), free T3 and free T4, or suffered from chronic illness were excluded.
The participants were randomly divided into 3 groups. One group was administered 8 g/day of high-quality fresh fish oil supplements, the second 8 g/day of oxidized fish oil supplements, and the third 8 g/day of high-oleic sunflower oil (HOSO) over a period of 7 weeks. The daily dose of EPA and DHA was 0·7 and 0·9 grams, respectively, in the two groups that were given fish oil supplements. Blood samples for the determination of cholesterol and TAG levels were collected before the study, 3 weeks into the study, and at the end of the study. The study examined the levels of IDL, LDL, HDL (high density lipoprotein), VLDL (very low density lipoprotein), the composition of the lipids (TAGs, phospholipids, unesterified cholesterol, or cholesteryl ester) bound to each of these four lipoprotein classes, and the apolipoproteins A1 (apoA1) and B (apoB).
The results showed that there was a significant decrease in the levels of IDL as well as small, medium, and large particles of LDL with fresh fish oil supplementation but significant increases in the levels of these metabolites with HOSO and stale fish oil. Furthermore, fresh fish oil significantly reduced the concentrations of total lipids, phospholipids, total cholesterol, cholesteryl esters and unesterified cholesterol in IDL and large, medium, and small LDL compared to HOSOS and oxidized fish oil. The median concentration of IDL and LDL particles decreased by 3% with fresh fish oil supplementation but increased by 5% and 11%, respectively, with HOSO and stale fish oil. However, there was no difference in the level of TAGs between the three participant groups. There were also no differences in the VLDL and HDL cholesterol levels between the three groups. The levels of ApoB were reduced in the fresh fish oil group but increased in the HOSO and oxidized fish oil groups; ApoA1 levels did not differ between groups.
One limitation of the study is the fact that numerous measurable parameters, which included different classes of lipoproteins and their lipid constituents, were determined without making the necessary statistical adjustments. This increases the statistical probability that a few of the associations drawn between fresh or stale fish oil consumption and changes in the blood levels of metabolites occurred by chance alone. However, the authors of the paper discount the possibility of such errors because the blood levels of these metabolites are linked and not independent: an increase in the level of one may affect the level of others. Another limitation was not taking account individual variations in the APOE4 gene among the participants. Variations in this gene have been shown previously to affect cholesterol and TAG profiles in response to fish oil supplementation.
To summarize, the study shows the importance of taking a high-quality fish oil supplement to truly reap its benefits. The process of oxidation commences as soon as the oil is exposed to air (or oxygen). Therefore, it is essential to carefully follow manufacturer guidelines with regard to the temperature and light conditions during storage. This is especially true of liquid fish oil; on the other hand, fish oil capsules may maintain their quality over long periods of storage at room temperature. Finally, fish oils that contain antioxidants, such as the vitamins C/E, and are packaged in dark bottles under nitrogen are more likely to preserve their efficacy.
Written By: Usha B. Nair, Ph.D.