Fish Oil: Benefits, Side Effects, and What You Need to Know

Fish oil has become one of the most popular dietary supplements in the United States, with millions of Americans taking it daily for various health benefits. Rich in omega-3 fatty acids, fish oil is touted for its potential to support heart health, reduce inflammation, and improve overall wellness. But does the science support these claims, and is fish oil right for you?

This comprehensive guide explores everything you need to know about fish oil supplements, including their benefits, potential risks, and how to use them safely.

What Is Fish Oil?

Fish oil is a dietary supplement extracted from the tissues of oily fish. It serves as a concentrated source of omega-3 fatty acids, which are essential nutrients that your body cannot produce on its own. These fatty acids must be obtained through diet or supplementation.

The two primary omega-3 fatty acids found in fish oil are:

• Docosahexaenoic acid (DHA) – Crucial for brain function and development
• Eicosapentaenoic acid (EPA) – Known for its anti-inflammatory properties

Fish oil supplements are available in multiple forms, including liquid, soft gel capsules, and pills, making them accessible and convenient for daily use.

Natural Sources of Omega-3 Fatty Acids

While supplements are popular, omega-3 fatty acids are best obtained from whole food sources. The richest natural sources include:

Fatty Fish

• Salmon (wild-caught preferred)
• Mackerel
• Sardines
• Herring
• Anchovies
• Trout

Shellfish

• Oysters
• Mussels
• Crabs
• Shrimp

Plant-Based Sources

Some plant foods contain alpha-linolenic acid (ALA), a different type of omega-3 fatty acid that the body can partially convert to EPA and DHA:

• Flaxseeds and flaxseed oil
• Chia seeds
• Walnuts
• Hemp seeds
• Soybeans

Health Benefits of Fish Oil

Research has investigated fish oil’s effects on numerous health conditions. Here’s what the scientific evidence reveals:

Cardiovascular Health

The relationship between fish oil and heart health is complex. Studies show that people who regularly consume fish as part of their diet (at least twice weekly) have a lower risk of heart disease and cardiovascular mortality. This benefit appears to come from eating whole fish rather than taking supplements.

Research on fish oil supplements for heart disease prevention has shown mixed results, with recent large-scale studies suggesting that supplementation provides little to no significant benefit for preventing heart attacks or strokes in the general population.

High Blood Pressure

Multiple clinical trials have demonstrated that fish oil supplementation can produce modest reductions in blood pressure. The effects appear to be dose-dependent, with higher doses typically producing greater reductions.

Evidence suggests that individuals with moderate to severe hypertension may experience more pronounced benefits compared to those with mild blood pressure elevation. The typical reduction ranges from 2-5 mmHg for systolic and 1-3 mmHg for diastolic blood pressure.

Triglycerides and Cholesterol

One of the most well-established benefits of fish oil is its ability to lower elevated triglyceride levels. Studies consistently show that omega-3 fatty acids can reduce triglycerides by 15-30%, particularly in individuals with significantly elevated levels.

The effects on cholesterol are more nuanced:

• HDL (“good”) cholesterol – May increase slightly
• LDL (“bad”) cholesterol – May increase slightly in some individuals
• Total cholesterol – Variable effects

If you have high triglycerides, consult your healthcare provider about whether fish oil supplementation is appropriate for you.

Inflammatory Conditions

Omega-3 fatty acids possess anti-inflammatory properties, which has generated interest in their use for inflammatory conditions.

Rheumatoid Arthritis: Research indicates that fish oil supplements may help reduce joint pain, morning stiffness, and tenderness in people with rheumatoid arthritis. While the relief is typically modest, some patients find it sufficient to reduce their reliance on anti-inflammatory medications. However, you should never adjust your medication regimen without consulting your doctor.

Brain and Mental Health

Omega-3 fatty acids, particularly DHA, are critical components of brain cell membranes. Some research has explored fish oil’s potential role in:

• Cognitive function and memory
• Depression and anxiety
• ADHD symptoms
• Age-related cognitive decline

While promising, evidence in these areas remains mixed, and more research is needed to draw definitive conclusions.

Recommended Dosage

There is no universal recommended dosage for fish oil, as appropriate amounts vary based on individual health status and goals. However, general guidelines include:

• General health maintenance: 250-500 mg combined EPA and DHA daily
• High triglycerides: 2-4 grams daily (under medical supervision)
• Inflammatory conditions: 1-3 grams daily

Always consult with a healthcare provider before starting fish oil supplementation, especially at higher doses.

Safety and Side Effects

When taken at recommended doses, fish oil supplements are generally considered safe for most people. However, they can cause side effects and may not be appropriate for everyone.

Common Side Effects

Mild side effects that some people experience include:

• Fishy aftertaste or burps
• Bad breath
• Nausea
• Upset stomach or diarrhea
• Heartburn
• Skin rash

Taking supplements with meals or freezing capsules before consumption may help reduce these gastrointestinal effects.

Potential Risks

Bleeding Risk: High doses of fish oil (typically above 3 grams per day) may increase bleeding risk by reducing blood clotting. This is particularly concerning for individuals taking blood-thinning medications or those with bleeding disorders.

Immune Function: Very high doses might suppress immune function, potentially reducing the body’s ability to fight infection.

Stroke Risk: Some research suggests that excessive fish oil intake might slightly increase the risk of hemorrhagic stroke, though this remains controversial.

Mercury Concerns: One advantage of fish oil supplements is that they typically contain little to no mercury, unlike some types of fish. Reputable manufacturers use purification processes to remove contaminants.

Who Should Be Cautious?

Certain individuals should exercise caution or avoid fish oil supplements:

• People with seafood allergies (safety is unclear)
• Those taking blood-thinning medications
• Individuals scheduled for surgery (may need to stop 2-3 weeks before)
• People with bleeding disorders
• Those with liver disease

Drug and Supplement Interactions

Fish oil can interact with various medications and supplements. Important interactions include:

Blood Thinners

Fish oil may enhance the effects of anticoagulant and antiplatelet medications, herbs, and supplements, potentially increasing bleeding risk. If you take blood thinners, medical supervision is essential.

Blood Pressure Medications

Because fish oil can lower blood pressure, combining it with blood pressure medications might cause blood pressure to drop too low. Monitor your blood pressure regularly if taking both.

Contraceptives

Some birth control medications may interfere with fish oil’s ability to lower triglycerides.

Weight Loss Medications

Certain weight-loss drugs may reduce the absorption of omega-3 fatty acids from fish oil. Taking them two hours apart may help prevent this interaction.

Vitamin E

Fish oil supplementation can reduce vitamin E levels in the body. Some fish oil products include vitamin E to compensate for this effect and prevent oxidation.

Choosing a Quality Fish Oil Supplement

Not all fish oil supplements are created equal. Consider these factors when selecting a product:

Purity and Testing

• Look for third-party testing certifications (USP, NSF International, or IFOS)
• Check for removal of heavy metals, PCBs, and other contaminants
• Verify the product is molecularly distilled or purified

Concentration

• Check the actual EPA and DHA content per serving
• Higher concentration means fewer pills needed
• Don’t be fooled by total fish oil amount – what matters is EPA/DHA content

Form

• Triglyceride form: Natural form found in fish, well absorbed
• Ethyl ester form: Concentrated but potentially less absorbable
• Phospholipid form: Found in krill oil, may have good absorption

Freshness

• Check expiration dates
• Look for products with antioxidants to prevent rancidity
• Store properly (cool, dark place or refrigerator)

Fish Oil vs. Eating Fish: Which Is Better?

While fish oil supplements offer convenience, eating actual fish provides several advantages:

• Whole fish contains protein, vitamins, minerals, and other beneficial nutrients
• The omega-3s in fish may be better absorbed than those in supplements
• Fish consumption is associated with better health outcomes in research
• Eating fish is generally safer than high-dose supplementation

The American Heart Association recommends eating fish (particularly fatty fish) at least twice per week. When prepared by baking, broiling, or grilling rather than frying, fish is an excellent addition to a healthy diet.

Supplements may be beneficial for those who:

• Don’t eat fish regularly
• Have documented omega-3 deficiency
• Have significantly elevated triglycerides
• Have rheumatoid arthritis or other inflammatory conditions

The Bottom Line

Fish oil supplements are a concentrated source of omega-3 fatty acids that may provide health benefits, particularly for reducing high triglycerides and possibly helping with inflammatory conditions like rheumatoid arthritis. However, eating fatty fish as part of a balanced diet appears to be more beneficial than supplementation for general heart health.

While generally safe when taken as directed, fish oil supplements can cause side effects and interact with medications. High doses may increase bleeding risk and should only be taken under medical supervision.

Before starting fish oil supplementation, consider whether you’re meeting your omega-3 needs through diet. If you decide supplements are right for you, choose a high-quality product and consult with your healthcare provider about appropriate dosing, especially if you have medical conditions or take medications.

Remember that supplements are meant to complement, not replace, a healthy diet. Focus on overall dietary patterns that include a variety of nutrient-rich foods, including fatty fish when possible, for optimal health outcomes.

Sources:

• Mayo Clinic – Fish Oil
• National Institutes of Health – Omega-3 Fatty Acids
• American Heart Association – Fish and Omega-3 Fatty Acids
• National Center for Complementary and Integrative Health – Omega-3 Supplements