Omega-3 and Omega-6 fish oils have been promoted not only for dyslexia and ADHD but also heart disease,high blood pressure, rheumatoid arthritis, asthma, bipolar disorder and cancer. In some cases there is good evidence to support fish oils as a treatment and in others the evidence is unclear. But what are the health risks of taking fish oils? Lots of producers of fish-oil capsules promote large dosages of supplements so are there any side effects from fish oils?
The US National Institute of Health classifies low intake of omega-3 fatty acids from fish as “Generally Regarded as Safe”. However they do highlight certain fish oil side effects that may trouble some people. The omega-3 in the fish oil may increase the risk of bleeding when taken in large doses. The bleeding can take the form of strokes, nosebleeds and blood in the urine. As the fish oils seem to decrease platelet aggregation, bleeding times may be longer.
A major worry with fish oils and the fish they are created from is poisoning from heavy metal and other pollutants. Mercury, dioxins and polychlorinated biphenyls (PCBs) are found in some species of fish. However, mostly this fish oil side effect is associated with eating fish directly as the oil, even in contaminated fish, carries little of the pollutants.
Stomach upset are a common side effect of fish oil supplements. Diarrhea may also occur, with potentially severe diarrhea at very high doses. There are also reports of increased burping, acid reflux/heartburn/indigestion, abdominal bloating, and abdominal pain. Fishy aftertaste is a common effect. Gastrointestinal side effects can be minimized if fish oils are taken with meals and if doses are started low and gradually increased.
People with low blood pressure or those taking blood-pressure reducing medicines should take care. One of the reported side effects of fish oil is a reduction of blood pressure. The impact on blood pressure appears to be dose dependent.
Vitamin E plays a part in metabolizing omega acids so large doses of fish oil place high demands on the body’s vitamin E supply. To avoid this fish oil side effect, vitamin E is added to many commercial fish oil products. As a result, regular use of vitamin E-enriched products may lead to elevated levels of this fat-soluble vitamin. Fish liver oil contains the fat-soluble vitamins A and D, and therefore fish liver oil products (such as cod liver oil) may increase the risk of vitamin A or D toxicity.
One side effect of fish oils and their fatty acids is an increase low-density lipoprotein levels (“bad cholesterol”) by 5-10%. This is dependent on the dose used. The oils have also been noted to have an effect on blood glucose levels in people with Type 2 / Adult Onset Diabetes but this is short-term and no long-term effects have been reported.
Overall omega-3 and 6 rich fish oils have few side effects and can be considered safe the vast majority of the population.
Source: Omega-3 fatty acids, fish oil, alpha-linolenic acid from the NIH.
See also: The Omega-3 Diet, ALA to DHA: The Fish Oil Alphabet and The Incredible Brain: A Miner Recovered.