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Fish Oil Side Effects

Fish oil is extracted from oily fish like Salmon, Mackerel and Cod, and as is the case with many supplements which are derived directly from edible sources, it is widely known as a very safe and well received product.

Fish Oil Benefits

One of the richest sources of essential omega-3 fatty acids docosahexaneoic acid (DHA) and eicosapentaenoic acid (EPA), it is used by a large number of people to attain or maintain good health, which it does in a variety of ways. It is endorsed by a number of health regulatory bodies, including the Australia Heart Foundation and the US National Institute of Health (NIH) for the treatment of conditions which include cardiovascular disease and arthritis.

While the RDI for omega-3 fatty acids is quite low and easily obtainable through diet alone, many of the well researched beneficial effects of DHA and EPA have been seen at doses which would be very difficult to consume through food alone. Subsequently, fish oil has become one of the most popular nutritional supplements on the market (1).

One of the reasons for the popularity of fish oil is its comparitive lack of side effects. For example, many physicians are now using fish oil as a first-line treatment for arthritis because it has significantly fewer adverse effects than the drugs that are usually used for treatment, including familiar, over the counter treatments like Ibuprofen (2). This does not mean that fish oil is completely without side effects. According to the pooled data from a number of trials involving fish oil, side effects are are recorded about 10% of the time, and these are generally mild (3).

Let's have a look at what users of fish oil should know.

Fish Oil Side Effects – Reflux, Gas and Digestive Disturbances

Digestive issues are by far the most frequent side effects related to fish oil consumption, responsible for about 80% of complaints (3). Reflux or "fish burps" is the most commonly cited problem. The stomach, particularly after eating, regularly expels gas into the oespohagus as a normal consequence of digestion. Fish oil has a lower density than water, so it has the tendency to float on top of the other stomach contents. As the fish oil is floating near the stomach's entrance, the act of burping can have the unfortunate side effect of introducing fish oil back into the oespohagus, giving the unpleasant sensation that the fish oil is "repeating". This can be lessened by breaking doses of fish oil up into smaller portions and taking them with, or immediately before meals, or the use of enteric-coated fish oil capsules which are designed not to split open until they have passed into the duodenum. Additionally, many manufacturers are now producing "odourless" fish oil capsules.

Other digestive disturbances reported include diarrhoea, particularly with larger doses, and nausea.

Fish Oil Side Effects – Mercury and other Toxins

For the past decade of so, we have been advised to restrict our oily fish intake to a few serves a week due to to possibility of high levels of mercury and other toxins like PCBs and dioxins. The good news is that fish oil is a great substitute for dietary fish oil because it is much lower in toxic substances. This is due to a few factors. Firstly, heavy metals like mercury tend to bind to protein, not fat, which means the majority of the contamination remains in the flesh of the fish, rather than the oil. Secondly, fish oil is often produced from small fish which feed on algae. It is the larger, predator fish that have the highest levels of toxin, because they feed on smaller prey fish over a longer time, accumulating their combined toxin load. On top of this, manufacturers are bound to both an international code of practice and local regulations, which set and enforce very low limits for permissable toxin levels (4). Fish oil is regularly found to contain much lower toxin levels than edible fish (5).

Fish Oil Side Effects - Bleeding

Fish oil is known to affect the platelets, which are the components of blood directly responsible for clotting. This effect is more likely to occur when high doses of more than 3g omega-3 are taken per day. Increased clotting time may produce symptoms such as easy bruising, profuse bleeding from wounds, nosebleeds, or blood in the stool. People experiencing these symptoms should immediately seek medical advice. Those who are taking blood thinning medication need to consult their doctor before taking fish oil, as their dosage may require adjustment (6).

Fish Oil Side Effects – Weight Gain

The highest recommended doses of fish oil only amount to a tiny fraction of the recommended daily energy intake. Fish oil will not cause weight gain. On the contrary, omega-3 compounds have shown promise as a support to weight loss.

Fish Oil Side Effects - Dosage

The US National Institute of Health has stated that doses of up to 3g of omega-3 per day are safe on a long-term basis. Fish oil varies in potency, so depending on the fatty acid make up in the product, this may represent a dose of more than 10mL of fish oil per day (6).

Fish oil is high in fat soluble vitamins A and D. Unlike water soluble vitamins, these are stored in the body indefinitely. While they are required for healthy body functioning, at high doses, they can be toxic. It is important not to exceed the maximum recommended dose of fish oil to avoid these effects, which can include bone fracture and liver disease.

Other Adverse Effects of Fish Oil

Fish oil is a natural substance but speaking to a medical professional before using this substance is a good idea, particularly for people intending to embark on a high-dose regime, women who are pregnant or breastfeeding, and the elderly. For those suffering from a chronic disease, consultation with a medical professional is imperitive, as fish oil has been known to affect blood sugar, blood pressure, cholesterol levels, oestrogen receptors, liver function, cancers, cardiac arrhythmias and bowel conditions in people with some pre-existing conditions. Naturally, people with known allergies or intolerances to fish should avoid fish oil and opt for one of the many alternative omega-3 sources on the market (6).

Side Effects of Fish Oil

While fish oil has the potential to exert a number of side effects, large-scale studies have concluded that these are uncommon and very likely to be mild and manageable (3) People with concerns are strongly encouraged to consult a doctor before using this supplement. For the vast majority of people, the benefits of fish oil far outweigh any negative effects.

(1) Nutrient Reference Values for Australia and New Zealand. Australian Government National Health and Medical Research Council and Ministry of Health Manatu Hauora. Accessed 30th April 2014.
(2) Leslie G Cleland, Michael J James, Susanna M Proudman. Fish oil: what the prescriber needs to know. Arthritis Res Ther. 2006; 8(1): 202.
(3) Villani, Anthony M; Crotty, Maria; Cleland, Leslie G; James, Michael J; Fraser, Robert J; Cobiac, Lynne; Miller, Michelle D (2013). "Fish oil administration in older adults: Is there potential for adverse events? A systematic review of the literature". BMC Geriatrics 13(1): 41. doi:10.1186/1471-2318-13-41. PMC 3664575.PMID 23634646.
(4) Review: Fish Oil and Omega-3 Fatty Acid Supplements Review (Including Krill, Algae, and Calamari Oil): Contaminants in Fish Vs. Supplements: Contaminants in Fish vs. Supplements". 13 August 2012. Accessed 30th April 2014.
(5) Mercury Levels in Commercial Fish and Shellfish (1990–2010) U.S. Food and Drug Administration. Accessed 30th April 2014.
(6) Fish Oil. Mayo Clinic. Accessed 30th April 2014.

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