Are there serious adverse effects of omega-3 polyunsaturated fatty acid supplements?

Dietary omega-3 polyunsaturated fatty acids (PUFAs) may reduce the risk of various diseases. Marine oils rich in omega-3 PUFAs have therefore become popular dietary supplements. Adverse effects need to be considered when administering omega-3 PUFAs. While unproblematic short-term adverse events linked to omega-3 PUFAs have been reported, long-term PUFA supplementation may be associated with increased cancer risk, possibly due to PUFAs, their oxidation products or added vitamin E. Large-scale trials have shown increased rates of prostate cancer in men taking α-tocopherol supplementation. Omega-3 PUFAs are highly prone to oxidative degradation to lipid peroxides and secondary oxidation products, which may render them ineffective or harmful. Oil contained in omega-3 supplements may contain a mixture of omega-3 PUFAs, problematic additives, and unspecified levels of potentially toxic oxidation products. The health consequences of oxidized fish oil intake remain unclear. Given the harmful effects of oxidized lipid products demonstrated in animal experiments, caution is needed in the supplementation of PUFAs at high doses over extended periods of time and during vulnerable phases of life, such as prenatal development, childhood, and adolescence. A balanced approach should weigh the overall health benefits of omega-3 PUFAs against potentially harmful effects of their supplementation. Future research should address the development of effective antioxidants without side effects.