It seems everyone has started taking some form of fish oil supplements and I am often asked “what are the side effects?” The fish oil craze started when studies in generally healthy adults with established coronary heart disease found that modest fish oil consumption (approximately 250 mg/day EPA+DHA) reduced the risk of death from heart disease. It has been suggested that most adults without known heart disease eat a diet containing at least one to two servings per week of oily fish which most of us don’t do.
When you don’t consume this much fish, a daily fish oil supplement should be considered and how much or what kind can be discussed with your doctor. But what are the potential side effects of taking fish oil supplements?
1) Mercury? Only a few large predator fish species (shark, swordfish, king mackerel, tilefish, and albacore tuna) contain appreciable amounts of mercury. Given cost considerations, such species are very rarely used to produce supplements. Similar to most fish species, commercially available fish oil capsules contain little to no mercury.
2) What about other contaminants? Fish oil capsules contain small amounts of polychlorinated biphenyls (PCBs) and dioxins with concentrations proportional to those in the fish species from which the fish oil is derived. Given the small absolute quantities of fish oil that would be consumed, the amounts of PCBs or dioxins that can be consumed from fish oil supplementation are extremely low.
3) Upset stomach? High doses may cause gastrointestinal upset, loose stools, and nausea. This is the most common side effect I hear about and usually in my patients taking 3000 mg a day or more.
4) Changes in blood sugar: Fish Oil supplements should be used with caution in diabetics as they may alter glucose regulation. Effects of drugs with hypoglycemic activity may be potentiated (including insulin and oral diabetes drugs). Blood sugar should be closely monitored, and the dosage of hypoglycemic medications may require adjustment.
5) Bleeding: Patients with a history of active bleeding (for example peptic ulcer, or stroke) should use fish oil supplements with caution. Also be careful if you are taking anticoagulant medications, including warfarin, aspirin, aspirin-containing products, NSAIDs, or antiplatelet agents (eg, ticlopidine, clopidogrel, dipyridamole).
6) Bleeding take #2: Discontinue use of fish oil supplements prior to dental or surgical procedures (generally at least 14 days before). This is important as there are frequent reports of postoperative bleeding complications in patients taking high doses of fish oil supplements (3000 mg a day or more).
7) Blood pressure: Fish oil may lower blood pressure so if you are on medications to lower your blood pressure be careful and closely monitor your blood pressure.
8) Fish allergy: This is obvious but if you have a known allergy or sensitivity to fish, talk to your doctor about which supplement you can take.
9) The Liver: The liver enzyme ALT may increase with use of fish oil supplements.
10) Cholesterol? Though fish oil lowers triglycerides it may increase LDL cholesterol in some patients, so that should be periodically monitored.