Cod Liver Oil & Fish Oil (Food View): Nutrients, What Research Shows and Safety

Cod liver oil is the oil taken from the liver of the cod. USDA also lists a salmon oil, which is pressed from the fish itself. [1] Both are almost pure fat and both contain the long-chain omega-3 fats called EPA and DHA. Cod liver oil also carries vitamins A and D, in amounts that vary from product to product. [2] People take these oils hoping to help the heart, joints, mood and immunity. This page looks at them as foods and keeps them apart from hype. The supplement side (capsules, brands, labels) has its own pages, linked at the bottom.

Read this first

• Cod liver oil is very rich in vitamin A. USDA lists 30,000 micrograms (mcg) of vitamin A (RAE) in 100 g, which is about 4,080 mcg in 1 tablespoon (13.6 g), or 453% of the FDA Daily Value. [1] The NHS says total vitamin A from food and supplements should average no more than 1.5 mg (1,500 mcg) a day, and that fish liver oil counts toward that total. [4] Real products differ from the USDA average, so the label matters. [2]
• Pregnancy: the NHS advises avoiding fish liver oil supplements when pregnant or trying for a baby, unless a GP advises otherwise, because they are high in vitamin A. [3] This is about vitamin A, not omega-3 itself.
• Fish allergy: fish is one of the major food allergens. [14] The NHS says people allergic to one fish often react to others, and that cooking does not lower the risk. [3] For trouble breathing or swelling of the face or throat, call 911 (or your local emergency number).
• Evidence in one line: pooled trials of omega-3 fats show a lowering of blood triglycerides (about 15%) and, with low certainty, a small drop in coronary heart events. [6] Cod liver oil itself did not prevent COVID-19 or other respiratory infections in a large trial. [7]
• Heart rhythm: pooled trials of marine omega-3 supplements found more atrial fibrillation (an irregular heartbeat). [8]

What is in it (USDA values)

The values below are for cod liver oil (USDA FoodData Central item 173577) and salmon oil (item 172343), both SR Legacy. [1] The serving column is the USDA household portion of 1 tablespoon, 13.6 g. USDA lists no protein, carbohydrate, fiber, sodium or other minerals in either oil.

% Daily Value uses the FDA 2016 Daily Values; the serving figures are the 100 g values multiplied by 0.136. USDA's items list the total polyunsaturated fat but not EPA and DHA separately, so we cannot give a gram figure for them from this data. USDA also lists a vitamin D value for both oils, but the cod liver oil figure is far lower than the 10 mcg of vitamin D that a Norwegian trial reported in just 5 mL of its cod liver oil, [7] so we do not repeat it here. Check the label for vitamin D.

Plant compounds do not apply here. The main active parts are the fats themselves: EPA and DHA (omega-3 fats from marine sources), described by NCCIH. [2]

What research says

Eaten as food vs taken as a supplement. Nearly all the trials above tested capsules or liquids at set amounts, not food. Eating oily fish is a different thing; see oily fish. Observational studies cannot prove cause. We did not check who paid for each trial because abstracts often do not say.

How much is a normal serving

USDA lists household portions of 1 teaspoon (4.5 g), 1 tablespoon (13.6 g) and 1 cup (218 g) for both oils, and about 123 kcal per tablespoon. [1] We found no official "normal serving" of cod liver oil. That is information, not a prescription: the label of the product and your clinician decide how much is right for you. For the fish itself, the NHS says adults should aim for at least two portions of fish a week, one of them oily (about 140 g cooked per portion), [3] and NCCIH says pregnant or breastfeeding women should eat 8 to 12 ounces of lower-mercury seafood a week. [2]

Safety, allergy and medicines

• Vitamin A and bones: the NHS says that averaging more than 1.5 mg (1,500 mcg) of vitamin A a day for many years may weaken bones and raise the risk of fractures, especially for older people and women after menopause. [4] A single tablespoon of cod liver oil at the USDA value is almost three times that figure. [1]
• Vitamin D: the NHS says not to take more than 100 mcg (4,000 IU) of vitamin D a day from all sources, with lower limits for children (50 mcg for ages 1 to 10, 25 mcg for babies). Too much can build up calcium in the body and harm bones, kidneys and heart. [5]
• Pregnancy and breastfeeding: avoid fish liver oil in pregnancy unless a GP advises otherwise. [3] The NHS also advises limiting oily fish to two portions a week in pregnancy. [13]
• Children: limits for vitamin A and D are lower for children. [4] [5] Ask a pediatrician before giving any cod liver oil.
• Fish allergy: see above. [3] [14] Packaged foods must name fish on the label under US law, but the rule has exemptions. [14]
• Medicines: the sources we read found no overall rise in bleeding with omega-3 supplements, but high-dose purified EPA showed a small rise. [9] NCCIH's page does not discuss interactions. [2] If you take blood thinners, tell your pharmacist. Vitamin A and D amounts also matter if you take other vitamin products.
• Heart rhythm: pooled trials found more atrial fibrillation with marine omega-3 supplements. [8] Ask a clinician if you have a heart rhythm condition.
• Side effects: NCCIH lists an unpleasant taste, bad breath, headache and stomach upset as usually mild effects. [2]
• Kidney disease and diabetes: we did not read a source that applies to these oils as a food. Ask your clinician.

Choosing, storing and food safety

• Quality varies. In New Zealand, 83% of 32 fish oil supplements tested exceeded the recommended level of one oxidation marker, and most contained less EPA and DHA than labeled. [11] A French study of 20 products found them within the same industry limits and not oxidized. [12] The studies do not name brands and results differ by country and year.
• Best-before date, price and origin were poor signs of quality in the New Zealand study. [11]
• We did not read an official storage rule for these oils, so follow the label. A sharp, rancid smell is a sign to throw the bottle away; this is a cautious general rule rather than a sourced one.

Related pages

• Fish oil vs cod liver oil
• Cod liver oil: vitamin A and D content and pregnancy caution
• Oily fish
• Omega-3 fatty acids in foods
• Foods in pregnancy: what official bodies advise
• Food allergy basics and emergency signs