Fish oil is well known for its wealth of health-promoting properties.
Rich in heart-healthy omega-3 fatty acids, fish oil has been shown to reduce blood triglycerides, relieve inflammation and even ease symptoms of conditions such as rheumatoid arthritis.
However, more fish oil is not always better, and taking too high a dose may do more harm than good to your health.
Here are eight potential side effects of consuming too much fish oil or omega-3 fatty acids.
1. High blood sugar
Some research shows that supplementing with high omega-3 fatty acids could increase blood sugar levels in people with diabetes.
One small study, for example, found that taking 8 grams of omega-3 fatty acids per day led to a 22% increase in blood sugar levels in people with type 2 diabetes over an eight-week period.
This is because large doses of omega-3s can stimulate glucose production, which can contribute to high long-term blood sugar levels.
However, other research has yielded conflicting results, suggesting that only very high doses impact blood sugar.
Another analysis of 20 studies found that daily doses of up to 3.9 grams of EPA and 3.7 grams of DHA — the two primary forms of omega-3 fatty acids — had no effect on blood sugar levels for individuals with type 2 diabetes.
Summary: Taking high doses of omega-3 fatty acids can stimulate glucose production, which may lead to increased blood sugar — though the scientific evidence is inconclusive.
Bleeding gums and nosebleeds are two hallmark side effects of excess fish oil consumption.
One study in 56 people found that supplementing with 640 mg of fish oil daily over a four-week period decreased blood clotting in healthy adults.
Additionally, another small study showed that taking fish oil may be linked to a higher risk of nosebleeds, reporting that 72% of adolescents taking 1–5 grams of fish oil daily experienced nosebleeds as a side effect.
For this reason, it’s often advised to stop taking fish oil before surgery and to talk to your doctor before taking supplements if you’re on blood thinners like Warfarin.
Summary: Taking large amounts of fish oil can inhibit blood clot formation, which may increase the risk of bleeding and cause symptoms such as nosebleeds or bleeding gums.
3. Low blood pressure
Fish oil’s capacity to lower blood pressure is well documented.
One study of 90 people on dialysis found that taking 3 grams of omega-3 fatty acids per day significantly decreased systolic and diastolic blood pressure compared to a placebo.
Similarly, an analysis of 31 studies concluded that fish oil could effectively lower blood pressure, especially for those with high blood pressure or high cholesterol levels.
While these effects can certainly be beneficial for those with high blood pressure, it can cause severe problems for those who have low blood pressure.
Fish oil may also interact with blood pressure-lowering medications, so it’s important to discuss supplements with your doctor if you’re receiving treatment for high blood pressure.
Summary: Omega-3 fatty acids have been shown to lower blood pressure, which may interfere with certain medications and cause problems for those with low blood pressure.
Diarrhea is one of fish oil’s most common side effects and may be especially prevalent while taking high doses.
One review reported that diarrhea is one of fish oil’s most common adverse effects, alongside other digestive symptoms such as flatulence.
In addition to fish oil, other types of omega-3 supplements may also cause diarrhea.
Flaxseed oil, for example, is a popular vegetarian alternative to fish oil but has been shown to have a laxative effect and may increase bowel movement frequency.
If you experience diarrhea after taking omega-3 fatty acids, take your supplements with meals and consider decreasing your dosage to see if symptoms persist.
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Summary: Diarrhea is a side effect of omega-3 fatty acid supplements such as fish oil and flaxseed oil.
5. Acid reflux
Although fish oil is known for its powerful effects on heart health, many people report feeling heartburn after starting to take fish oil supplements.
Other acid reflux symptoms — including belching, nausea, and stomach discomfort — are common side effects of fish oil due mainly to its high-fat content. Fat has been shown to trigger indigestion in several studies.
Sticking to a moderate dose and taking meal supplements can reduce acid reflux and relieve symptoms.
Additionally, splitting your dose into a few smaller portions throughout the day may help eliminate indigestion.
Summary: Fish oil is high in fat and may cause acid reflux symptoms such as belching, nausea, indigestion, and heartburn in some people.
6. Hemorrhagic stroke
Hemorrhagic stroke is a condition characterized by bleeding in the brain, usually caused by the rupture of weakened blood vessels.
Some animal studies have found that high omega-3 fatty acids could decrease the blood’s ability to clot and increase the risk of hemorrhagic stroke.
These findings are consistent with other research showing that fish oil could inhibit blood clot formation.
However, other studies have mixed results, reporting no association between fish and fish oil intake and hemorrhagic stroke risk.
Further human studies should be conducted to determine how omega-3 fatty acids may impact the risk of hemorrhagic stroke.
Summary: Some animal studies have found that a high intake of omega-3 fatty acids could increase the risk of hemorrhagic stroke, while other human studies have found no association.
7. Vitamin A toxicity
Certain omega-3 fatty acid supplements are high in vitamin A, which can be toxic if consumed in large amounts.
For example, just one tablespoon (14 grams) of cod liver oil can fulfill up to 270% of your daily vitamin A needs in one serving.
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Vitamin A toxicity can cause side effects such as dizziness, nausea, joint pain, and skin irritation.
Long term, it could also lead to liver damage and even liver failure in severe cases.
For this reason, it’s best to pay close attention to the vitamin A content of your omega-3 supplement and keep your dosage moderate.
Summary: Certain omega-3 fatty acid supplements, such as cod liver oil, are high in vitamin A, which can be toxic in large amounts.
Some studies have found that taking moderate doses of fish oil could enhance sleep quality.
For instance, one study of 395 children showed that taking 600 mg of omega-3 fatty acids daily for 16 weeks helped improve sleep quality.
In some cases, taking too much fish oil may interfere with sleep and contribute to insomnia.
In one case study, it was reported that taking a high dose of fish oil worsened symptoms of insomnia and anxiety for a patient with a history of depression.
However, current research is limited to case studies and anecdotal reports.
More research is needed to understand how large doses affect sleep quality in the general population.
Summary: Although moderate doses of fish oil have been shown to improve sleep quality, one case study suggests that taking large amounts caused insomnia.
How much fish oil is too much?
Although recommendations can vary widely, most health organizations recommend an intake of at least 250–500 milligrams of combined EPA and DHA, the two essential omega-3 fatty acids, per day.
However, a higher amount is often recommended for people with certain health conditions, such as heart disease or high triglyceride levels.
For reference, a typical 1,000-mg fish oil softgel generally contains about 250 mg of combined EPA and DHA, while one teaspoon (5 ml) of liquid fish oil packs in around 1,300 mg.
According to the European Food Safety Authority, omega-3 fatty acid supplements can be safely consumed at doses up to 5,000 mg daily.
As a general rule of thumb, if you experience any adverse symptoms, simply decrease your intake or consider meeting your omega-3 fatty acid needs through food sources instead.
Summary: Up to 5,000 mg of omega-3 fatty acids daily is safe. If you experience adverse symptoms, decrease your intake or switch to food sources.
Omega-3 is an essential part of the diet, and supplements like fish oil have several health benefits.
However, consuming too much fish oil could actually take a toll on your health and lead to side effects such as high blood sugar and an increased risk of bleeding.
Stick to the recommended dosage and aim to get most of your omega-3 fatty acids from whole food sources for the most nutritional gain.