Alpha-Linolenic Acid (18:3n-3)
Although flaxseed oil is generally well tolerated, high doses may cause loose stools or diarrhea (151). Allergic and anaphylactic reactions have been reported with flaxseed and flaxseed oil ingestion (152).
Eicosapentaenoic Acid (20:5n-3) and Docosahexaenoic Acid (22:6n-3)
Serious adverse reactions have not been reported in those using fish oil or other EPA and DHA supplements. The most common adverse effect of fish oil or EPA and DHA supplements is a fishy aftertaste. Belching and heartburn have also been reported. High doses may cause nausea and loose stools.
Potential for Excessive Bleeding: The potential for high *****-3 fatty acid intakes, especially EPA and DHA, to prolong bleeding times has been well studied, and may play a role in the cardioprotective effects of *****-3 fatty acids. Although excessively long bleeding times and increased incidence of hemorrhagic stroke have been observed in Greenland Eskimos with very high intakes of EPA + DHA (6.5 g/day), it is not known whether high intakes of EPA and DHA are the only factor responsible for these observations (1). The US FDA has ruled that intakes up to 3 g/day of long-chain *****-3 fatty acids (EPA and DHA) are Generally Recognized As Safe (GRAS) for inclusion in the diet, and available evidence suggests that intakes less than 3 g/day are unlikely to result in clinically significant bleeding (3). Although the Institute of Medicine did not establish a tolerable upper level of intake (UL) for *****-3 fatty acids, caution was advised with the use of supplemental EPA and DHA, especially in those who are at increased risk of excessive bleeding (see Drug Interactions below) (1).
Potential for Immune System Suppression: Although the suppression of inflammatory responses resulting from increased *****-3 fatty acid intakes may benefit individuals with inflammatory or autoimmune diseases, anti-inflammatory doses of *****-3 fatty acids could decrease the potential of the immune system to destroy pathogens (153).
Studies comparing measures of immune cell function outside the body (ex vivo) at baseline and after supplementing people with *****-3 fatty acids, mainly EPA and DHA, have demonstrated immunosuppressive effects at doses as low as 0.9 g/day for EPA and 0.6 g/day for DHA (1). Although it is not clear if these findings translate to impaired immune responses in vivo, caution should be observed when considering *****-3 fatty acid supplementation in individuals with compromised immune systems.