Mega dosing fish oil supplements: some safety considerations
We all like our fish oil supplements and with reason. Well-known benefits of the omega-3 fatty acids in fish oil are their ability to lower circulating triglycerides and blood pressure. Less proven are the claims regarding anxiety, depression, vision and cancer. These days a lot of nutrition gurus and supplement companies are trying to sell you the idea that “more is better”. They sometimes advice the most ridiculous intakes in order to sell more of their products. It is important to know that high intakes of fish oil supplements may come with minor side effects such as a fishy aftertaste, diarrhea, nausea, belching and heartburn (1). These “minor” discomforts can be reduced by dividing your daily intake up into two or three smaller doses taken together with a meal. However, mega dosing EPA and DHA has also the potential to induce more severe side effects.
1) Prolonged bleeding times:
This has been less established, but there is some data indicating that high intakes of EPA and DHA have the capacity to extend bleeding times. This story came to the surface after excessively long bleeding times and increased incidence of hemorrhagic stroke were observed in Greenland Eskimos (2-3). Their omega-3 intake reached levels of 13.7 g/3000 kcal/day (4). High doses of EPA+DHA may decrease platelet aggregation and therefore may influence bleeding time. However, a review that examined the link between bleeding after cardiovascular procedures and fish oil intakes, found no significant risk of bleeding (5). Nevertheless, in some individuals combined intakes exceeding 3g of DHA+EPA a day, may result in excessive bleeding (6).
2) Suppressed immune response
A suppressed immune response may be helpful for people suffering from an autoimmune –or inflammatory disease. However, this does not apply to healthy elderly people. In a study from Thies and colleagues, healthy elderly subjects were submitted to a 12-week trial in which they daily received capsules filled with 4g placebo oil (an 80:20 mix of palm and sunflower seed oils) or blends of placebo oil and 2g ALA, 770 mg GLA, 680 mg AA, 720 mg DHA, or 1 g EPA + DHA (720 mg EPA + 280 mg DHA). Total fat intake from the capsules was 4 g/d. Only the addition of 280 mg of DHA to 720 mg of EPA reduced natural killer cell activity with 48% (7). This significant reduction in NK cell activity was fully reversed 4 weeks after finishing supplementation. In another study conducted by Rees et al, healthy young and older men received 9 placebo capsules (corn oil) or 9 capsules containing oil that provided 1.35, 2.7, or 4.05 g EPA/d for 12 weeks (8). Only in the older men, EPA supplementation caused a dose-dependent decrease in neutrophil respiratory burst. From these 2 studies, we can conclude that for healthy elderly people or people with an already weakened immune system, taking high dosages of fish oil may not be such a good idea. Natural killer cells and neutrophils both belong to the innate immune system and form our first line defense against pathogens. Thus, taking high intakes of EPA+DHA may hamper your immune response.
There is some data available showing that reasonable intakes of fish oil (1-3g of EPA+DHA/day) is beneficial for our health, but don’t overdo it. For healthy people it is just not necessary to take more than 3g of EPA+DHA per day. According to the FDA, intakes up to 3g of combined EPA+DHA can be considered to be safe, so why would you take more and risk side effects ?
- Kris-Etherton, P.M., W.S. Harris, and L.J. Appel, Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation, 2002. 106(21): p. 2747-57.
- Ostergaard Kristensen, M., Increased incidence of bleeding intracranial aneurysms in Greenlandic Eskimos. Acta neurochirurgica, 1983. 67(1-2): p. 37-43.
- Dyerberg, J. and H.O. Bang, Haemostatic function and platelet polyunsaturated fatty acids in Eskimos. Lancet, 1979. 2(8140): p. 433-5.
- Bang, H.O., J. Dyerberg, and H.M. Sinclair, The composition of the Eskimo food in north western Greenland. The American journal of clinical nutrition, 1980. 33(12): p. 2657-61.
- Office of Nutritional Products, Labeling, and Dietary Supplements, Center for Food Safety and Applied Nutrition, US Food and Drug Administration. Letter responding to a request to reconsider the qualified claim for a dietary supplement health claim for omega-3 fatty acids and coronary heart disease. Docket No. 91N-0103. February 8, 2002.
- Harris, W.S., Expert opinion: omega-3 fatty acids and bleeding-cause for concern? The American journal of cardiology, 2007. 99(6A): p. 44C-46C.
- Thies, F., et al., Dietary supplementation with eicosapentaenoic acid, but not with other long-chain n-3 or n-6 polyunsaturated fatty acids, decreases natural killer cell activity in healthy subjects aged >55 y. The American journal of clinical nutrition, 2001. 73(3): p. 539-48.
- Rees, D., et al., Dose-related effects of eicosapentaenoic acid on innate immune function in healthy humans: a comparison of young and older men. The American journal of clinical nutrition, 2006. 83(2): p. 331-42.