What happened to your body when you start taking cod liver oil?

October 8, 2025 •

2 min read

Used for centuries to treat conditions like joint pain and rickets, cod liver oil is a time-tested supplement. When you start taking cod liver oil, your body receives a potent dose of essential nutrients, leading to both beneficial changes and some potential side effects.

Quick Summary

An intake of cod liver oil provides omega-3 fatty acids, vitamin A, and vitamin D, supporting heart, bone, eye, and brain health while reducing inflammation. High doses can lead to toxicity, and interactions with certain medications are possible.

Key Points

Reduced Inflammation: Cod liver oil's omega-3s, EPA and DHA, help suppress inflammatory proteins, which can lead to reduced joint pain and stiffness over time.
Improved Cardiovascular Health: The supplement can lower blood triglycerides, raise HDL cholesterol, and may support blood pressure management, which benefits overall heart health.
Stronger Bones and Immunity: Rich in vitamins A and D, cod liver oil enhances calcium absorption for bone health and strengthens the immune system to fight off infections.
Enhanced Eye and Brain Function: The high vitamin A content supports vision, while DHA is a key component for brain and cognitive health.
Risk of Toxicity: Overdosing is a significant risk due to the fat-soluble vitamins A and D, which can build up in the liver and cause serious health issues.
Potential for Contaminants: As with other fish oils, there is a risk of contaminants like mercury; choosing a purified, reputable brand is crucial for safety.
Important Drug Interactions: Cod liver oil can thin the blood and may interact with medications for high blood pressure, diabetes, and blood clotting.

Cod liver oil, sourced from the liver of Atlantic cod, differs from regular fish oil by providing a blend of omega-3 fatty acids (EPA and DHA) along with significant amounts of vitamins A and D. This supplement can bring about various changes in the body, impacting cardiovascular, skeletal, and immune health.

The immediate effects of taking cod liver oil

Initial effects within a few weeks may include reduced inflammation and related joint discomfort. The omega-3s help reduce pro-inflammatory substances. However, digestive issues like a fishy aftertaste or nausea can occur initially, often alleviated by taking the oil with food or opting for capsules.

Impact on cholesterol and blood triglycerides

Cod liver oil is known to improve blood lipid levels. Its omega-3s can lower triglycerides by 20% to 50% and may slightly increase HDL cholesterol, contributing to better heart health. It is important to view it as a supplement, not a medical treatment replacement.

The long-term effects of supplementing with cod liver oil

Over time, the combined effects of omega-3s and vitamins become more noticeable, affecting multiple body systems.

Improvements in bone and joint health

Vitamin D is crucial for calcium absorption and bone strength, helping to prevent osteoporosis over time. Continued omega-3 intake can further help manage joint pain and stiffness.

Enhanced immune function and eye health

Both vitamins A and D in cod liver oil support immune function. Vitamin A is essential for immune cells and vision, while vitamin D regulates immune responses. This can help the body defend against infections. Omega-3s and vitamin A also benefit eye health, potentially lowering the risk of certain eye conditions.

Cognitive and mental well-being

DHA, a key omega-3, is vital for brain structure and cognitive function. Some research suggests long-term use may help reduce depressive symptoms.

Risks and considerations

While safe in recommended doses, excessive intake can lead to vitamin A and D toxicity, causing symptoms like nausea and headaches, and potentially liver damage. Choosing purified brands is important to avoid contaminants like mercury. Cod liver oil can also thin the blood and may interact with medications for blood thinning or diabetes.

Cod liver oil vs. regular fish oil: A comparison


Feature	Cod Liver Oil	Regular Fish Oil
Source	Liver of codfish only	Flesh of various oily fish (e.g., salmon, mackerel)
Primary Nutrients	Omega-3s (EPA, DHA), high vitamins A & D	High concentration of omega-3s (EPA, DHA)
Vitamin A Content	Significantly higher	Low to none
Vitamin D Content	Significantly higher	Low to none (unless added)
Best for...	Supporting bone health, immunity, eye health, joint pain	General inflammation, heart health (higher omega-3 load)

Conclusion

Incorporating cod liver oil into your diet can offer benefits like reduced inflammation, improved joint and bone health, and better cardiovascular function. However, its high vitamin A and D content necessitates careful dosing to avoid toxicity. Always choose a reputable, tested brand. Consulting a healthcare professional before starting supplements is recommended, especially if pregnant, managing a chronic condition, or taking medications.

Frequently Asked Questions

Cod liver oil is extracted specifically from the liver of codfish and contains high levels of vitamins A and D in addition to omega-3 fatty acids. Regular fish oil is extracted from the flesh of various fatty fish and contains a higher concentration of omega-3s but little to no vitamins A and D.

While individual results may vary, some people with joint pain may notice improvement within 2 to 6 weeks of consistent daily use. For other benefits, such as cardiovascular or bone health, it can take longer, typically a few months.

Yes, taking too much cod liver oil, particularly over a long period, can lead to vitamin A and D toxicity. Since these are fat-soluble vitamins, they can build up in your body to dangerous levels. It is essential to follow the recommended daily dosage.

Common side effects can include a fishy taste, bad breath, upset stomach, heartburn, and nausea. These are generally mild and can be minimized by taking the supplement with meals.

Cod liver oil can interact with certain medications. Because it can slow blood clotting, it is not recommended for people on blood thinners. It can also affect blood pressure and blood sugar levels, so those on related medications should consult a doctor first.

Pregnant or breastfeeding women should avoid high doses of cod liver oil due to the risk of vitamin A toxicity, which can harm a baby. Individuals with fish allergies or those on blood-thinning medication should also exercise caution or avoid it entirely.

Look for supplements from reputable brands that are independently tested for purity and contaminants like heavy metals. Certification seals from organizations such as USP or ConsumerLab can indicate a safe product.