The Food and Nutrition Board did not set an Upper Level of known safe intake because of inadequate data and difficulties translating test tube study findings to living organisms including humans. We know that Greenland Eskimos consume about 6.5 g/day, whereas USA dietary intakes are considered high when they reach 1.3 g/day. In a study about cellular response to eating omega-3 fortified foods, no adverse effects were reported when subjects consumed up to 10.8 g a day (1.8 g/d of EPA and DHA and 9.0 g ALA) over a 4 week period [Mantzioris E., Cleland LG, Gibson RA, et al. Am J Clin Nutr 2000;72:42-8] without any reports of adverse effects. The Food and Nutrition Board cautions that high intakes may impair the immune response and cause prolonged bleeding. While these side effects are rare with foods, their likelihood is greater with supplement use such as fish oil capsules and flaxseed oil.
Persons with diabetes or glucose intolerance should use omega-3 fats, especially omega-3 supplements under the care of a medical professional because they may reduce glucose tolerance, thus causing more diabetic-like symptoms. In fact, oral diabetes medication doses may need to be increased with omega-3 supplement use. Anticoagulants such as aspirin or coumadin prolong bleeding times as do some herbs such as ginko. Persons taking any medications or using herbal supplements should consult their physician to minimize the possibility of these harmful side effects.