Cod liver oil is the golden-yellow oil from the liver of cod – and a piece of nutritional history that can still be found in many kitchens and home medicine cabinets today. Anyone who was given a spoonful as a child usually remembers it very clearly. This overview tells you where cod liver oil comes from, what is in it, how to fit it pleasantly into your day today, and which ideas from the kitchen and your daily routine can brighten the dark season.
Cod liver oil has a history that stretches from the Lofoten Islands to a children's clinic in Vienna
The German word "Tran" still causes a stubborn misunderstanding. It originally referred to oil rendered from the blubber of marine mammals, which served as lamp oil for centuries. Cod liver oil has nothing to do with that: it comes from the liver of cod and related fish. That many people still think of whales when they hear the word is one of the small curiosities of the German language.
A large part of the story takes place in the North Atlantic. Every winter, cod travel to the coast of northern Norway to spawn, and around the Lofoten Islands this grew into one of Europe's great seasonal fisheries. Where a lot of fish was landed, a lot of livers accumulated too. One background report describes a traditional oil works on the Lofoten Islands where cod liver oil was made by time-honoured methods and where visitors liked to take home a bottle as a souvenir. As a tonic of the home medicine cabinet, cod liver oil has been known in Europe since the 19th century, and in Norway it remains a tradition to take a spoonful in winter when daylight is scarce.
The scientific side is particularly interesting. In the early 1920s, the British researcher Edward Mellanby observed that dogs fed cod liver oil did not develop rickets – the bone disease in children caused by a lack of vitamin D. The American Elmer McCollum then heated cod liver oil until the vitamin A it contained was destroyed. The oil still kept its ability to prevent rickets. So there had to be another substance in it, which he named "vitamin D" as the fourth vitamin to be discovered. At the same time, the researcher Harriette Chick studied children in Vienna and described cod liver oil and sunlight as two ways of addressing rickets. Cod liver oil therefore stands at the beginning of our present-day knowledge about vitamin D.
And the spoonful of childhood? It shaped generations: bitter, oily, but a reliable part of the winter months. Today things are very different. Cod liver oil is available as a mildly processed oil, often with lemon flavour, and as a capsule you simply take with a glass of water. The old classic is enjoying its comeback precisely because it is so much more pleasant now.
A teaspoon of cod liver oil contains omega-3, vitamin A, vitamin D and vitamin E
Cod liver oil is an all-rounder among foods because it bundles several nutrients into one small portion. All of them belong to the group of fat-soluble nutrients: they are absorbed particularly well together with some fat, and the oil supplies exactly that itself. First, cod liver oil contains the long-chain omega-3 fatty acids EPA and DHA. Second, it contains vitamin A, vitamin D and vitamin E. How much of each is in a product differs considerably depending on processing and manufacturer. For orientation, take the composition of the cod liver oil used in a large Norwegian study with around 34,000 adults (RCT in humans): it supplied 5 ml per day, roughly one teaspoon.
| Nutrient | Amount per teaspoon (5 ml) | Also found in |
|---|---|---|
| Vitamin D3 | approx. 10 µg (400 IU) | oily fish, egg yolk, sunlight on the skin |
| Vitamin A | approx. 250 µg | eggs, butter, liver; as a precursor in carrots, sweet potatoes, kale |
| EPA | approx. 0.4 g | herring, mackerel, salmon, sardines, algae oil |
| DHA | approx. 0.5 g | herring, mackerel, salmon, sardines, algae oil |
| Vitamin E | approx. 3 mg | nuts, seeds, plant oils |
Each of these nutrients has its own role in the body. Vitamin D is involved in the absorption of calcium and phosphorus and therefore in normal bones, teeth and muscles. Vitamin A is involved in the process of vision and in the maintenance of normal skin and mucous membranes. EPA and DHA are building blocks of cell membranes, and DHA occurs particularly abundantly in the brain and the retina. Vitamin E is one of the antioxidants, the substances that react with oxygen compounds in the cells, and it is found in plenty in nuts, seeds and plant oils.
A word on vitamin A, so the enjoyment lasts: the principle here is "good, but in moderation". In 2024 the European Food Safety Authority (EFSA) confirmed a tolerable upper intake level of 3,000 µg retinol equivalents per day for adults from all sources, including pregnant and breastfeeding women. How much vitamin A a cod liver oil product supplies varies widely. A look at the label is therefore worthwhile, especially if you also take a multivitamin or often eat liver. Pregnant and breastfeeding women are best advised to discuss cod liver oil and any other vitamin A supplement with their doctor first.
As oil, capsule or with lemon flavour: how to find the form that suits you
The classic variety is the liquid oil. It can be portioned precisely and suits everyone who finds capsules hard to swallow. Most mildly processed oils today have a fresh lemon taste and hardly any of the fishy aftertaste of the past. If you don't like the spoon straight, stir the oil into yoghurt, a smoothie or quark with berries. The fat in the yoghurt additionally makes it easier to absorb the fat-soluble vitamins.
Capsules are the convenient travel option: no spoon, no taste, no stains in your bag. They are swallowed whole with a drink, ideally with a meal. The label states the amounts per capsule, and that is exactly where comparing pays off: some capsules contain a small amount of cod liver oil, others considerably more, and some have added vitamins.
Whether oil or capsule: the substances in cod liver oil are sensitive to light, heat and air. Store the product dark, cool and tightly closed, as described on the pack. The oil should smell fresh, mildly of the sea, not sharp or rancid. If you are allergic to fish, leave cod liver oil out. If you take blood-thinning medication, discuss taking it with your doctor beforehand, because omega-3 fatty acids have to do with blood clotting.
Cod liver, herring and mackerel bring the north into your kitchen
Cod liver oil can be wonderfully complemented by foods that deliver the same nutrients on your plate. That starts with the fish cod liver oil comes from in the first place. Cod liver is available canned and is a prized delicacy in northern Europe. The oil from it tastes much milder than classic cod liver oil. Because liver also contains a lot of vitamin A, it is best enjoyed as an occasional treat rather than a daily ingredient. According to the EFSA opinion, vitamin A intake in Europe stays in a good range if liver and liver products are eaten no more than once a month.
A few simple ideas for everyday life:
- Cod liver toast: Well-drained cod liver on toasted wholemeal bread, with lemon zest, chives and freshly ground pepper. Serve with cucumber slices.
- Herring salad: Matjes or mildly pickled herring with apple, beetroot, cucumber and a sauce of yoghurt, dill and a little horseradish. Serve with boiled potatoes.
- Oven-baked mackerel: Roast mackerel fillets on slices of fennel and lemon in the oven and serve with potatoes.
- Trout or char: From Swiss farms, in the oven or in the pan with herb butter and seasonal vegetables.
- Sardines on bread: Tinned fish with onion rings, parsley and a squeeze of lemon is ready in two minutes.
The plant side also offers building blocks for a plate that suits the nutrients in cod liver oil. Vitamin A occurs as a precursor in orange and dark green vegetables such as carrots, pumpkin, sweet potatoes, kale and spinach. A splash of oil on the vegetables makes absorption easier. Egg yolk and oily fish supply vitamin D, one more reason for the Sunday breakfast egg.
Omega-3 also works without fish: algae are the original source
A nice twist in the story of cod liver oil: fish do not make their long-chain omega-3 fatty acids themselves. They take them up because they eat microalgae and animals that feed on algae. The actual producers of EPA and DHA are tiny algae in the sea. That opens a second door for everyone who avoids fish, doesn't like it or prefers to eat vegan: omega-3 from algae oil supplies the same fatty acids straight from the source. You can find more in our article on omega-3 from algae oil.
In the kitchen the plant route can be nicely complemented. Linseed oil, flaxseed, chia seeds and walnuts supply alpha-linolenic acid, ALA for short, a plant-based omega-3 fatty acid. It is a valuable part of a varied diet. EPA and DHA, by contrast, come directly from sea fish or microalgae. A spoonful of freshly ground flaxseed in your muesli or a handful of walnuts in a salad is an ideal addition to both routes.
Ten everyday tips for cod liver oil, omega-3 and the dark season
1. Take daylight with you every day
The best ritual in the vitamin D story costs nothing: go outside. The Viennese investigations of the 1920s already described sunlight and cod liver oil as two routes to vitamin D. Especially in the dark months a lunchtime walk is worthwhile, even when the sky is grey. A quarter of an hour outdoors is a gain for mood and rhythm anyway.
2. Always take cod liver oil with a meal
Vitamins A, D and E are fat-soluble. With a meal that contains some fat – a breakfast egg, nuts, yoghurt, olive oil on a salad – absorption works best. The time in the middle of the day is therefore less important than the habit of having something on your plate.
3. Build a fixed routine
Link the spoon or the capsule to an anchor point: the first cup of tea in the morning, brushing your teeth, your breakfast yoghurt. That way nothing gets forgotten, and it becomes a small ritual among the calm moments of the day. Put the bottle in plain view next to the coffee machine or the kettle.
4. Put fish on the table once or twice a week
Fish is the classic source of EPA and DHA. Many nutrition experts recommend one to two fish meals per week, preferably including one with oily fish such as herring, mackerel or salmon. This combines wonderfully with recipes like the ones above and brings variety to the weekly plan.
5. Eat colourful and seasonal
Pumpkin, carrots, beetroot, cabbage, apples and nuts are available in Switzerland in top quality in autumn and winter. The more colourful the plate, the broader the range of nutrients. Orange and dark green vegetables also supply the precursor of vitamin A, which the body converts itself when needed.
6. Bring plant-based omega-3 into the kitchen
Grind flaxseed fresh, add chia to your porridge, sprinkle walnuts over salads and vegetables. Linseed oil tastes excellent cold over boiled potatoes and quark but should not be heated. Kept tightly closed and dark in the fridge, it stays fresh for longer.
7. Keep moving – especially outdoors
Walking, cycling, hiking, a short bodyweight workout: exercise keeps muscles and bones active in everyday life and brings daylight into play at the same time. Two small sessions a week with squats, lunges and push-ups are a good start.
8. Look after good sleep
A calm evening routine with dimmed light, a cup of herbal tea and a fixed bedtime window makes the dark season cosier. Sleep rhythm and morning daylight work closely together, which is why tip 1 fits right in.
9. Have your blood values checked by your GP
If you want to know where you stand, ask your GP to measure your vitamin D level. It gives orientation for the winter months. If your calcium levels are raised, or if you already take a vitamin D supplement, discuss cod liver oil with your doctor beforehand so that the total amount is right.
10. Pay attention to quality and the label
Good cod liver oil products state the fish species, the origin and the amount per portion for vitamin A, vitamin D, EPA and DHA. Check the shelf life, look for dark glass or light-protective packaging and ask at the pharmacy if you are unsure. Important: take only the amount stated on the pack and always count other preparations containing vitamins A and D.
Omega-3 Algae Oil Forte: EPA and DHA straight from the alga
If you would like the omega-3 fatty acids from cod liver oil without fish, Natura Nova's Omega-3 Algae Oil Forte offers a vegan alternative. It supplies 500 mg DHA and 250 mg EPA per daily dose (2 capsules), obtained from specially cultivated microalgae. The capsule shell is vegan, and the brown glass protects the delicate fatty acids from light.
Conclusion: an old classic that fits easily and deliciously into everyday life today
Cod liver oil connects history, kitchen and daily life. It stood at the beginning of the discovery of vitamin D, has accompanied winter in the north for generations and has developed from a dreaded spoonful into a mildly processed oil or a handy capsule. Added to that are the many building blocks everyone has in their own hands: daylight, fish and seasonal vegetables, flaxseed and walnuts, a fixed place for the daily routine and good sleep habits. Anyone who combines all of this goes into the dark season well prepared. And whoever would rather do without fish has a second route to EPA and DHA with algae oil.
This article provides general information about cod liver oil and does not replace medical advice, diagnosis or treatment. If you have health complaints, please consult a doctor or pharmacist.
Sources
- Brunvoll SH et al.: Prevention of covid-19 and other acute respiratory infections with cod liver oil supplementation, a low dose vitamin D supplement: quadruple blinded, randomised placebo controlled trial. BMJ 2022;378:e071245. RCT (human), used here for the composition of the cod liver oil employed. PMC9449357, doi:10.1136/bmj-2022-071245
- DeLuca HF: History of the discovery of vitamin D and its active metabolites. BoneKEy Reports 2014;3:479. Narrative review. PMC3899558
- Rajakumar K: Vitamin D, cod-liver oil, sunlight, and rickets: a historical perspective. Pediatrics 2003;112(2):e132–e135. Narrative review. PMID 12897318
- Academy of Nutrition Sciences: Vitamin D: One hundred years on (on the Viennese investigations by Chick et al. 1922). Narrative review. academynutritionsciences.org.uk
- EFSA NDA Panel: Scientific opinion on the tolerable upper intake level for preformed vitamin A and β-carotene. EFSA Journal 2024;22(6):e8814. Scientific opinion. PMC11154838, doi:10.2903/j.efsa.2024.8814
- Den Store Danske (Lex.dk): Tran. Encyclopaedia entry on oil from the blubber of marine mammals. lex.dk/tran
- Planet Wissen: Stärkungsmittel Lebertran. Background report. planet-wissen.de
