As per the label. Watch the vitamin A dose.
A good combined source when there is a deficiency.
May somewhat reduce the need for anti-inflammatories.
View the study (RCT) →⏱ 3 min read
Cod liver oil is one of the nutritional supplements with the longest and best-documented clinical history: it has been used in European pharmacopoeias since the 18th century for the prevention and treatment of childhood rickets, first as folk medicine and later on a scientific basis when, in the early 20th century, vitamins A and D were identified as the active principles responsible for its efficacy; for several generations, a daily spoonful of cod liver oil was part of children's rations in climates with little winter sun exposure, and it is one of the first historical examples of systematic nutritional prevention on a population scale, before food fortification and synthetic vitamin supplements existed.
Unlike conventional fish oil (extracted from the muscle and viscera of small fish such as anchovy, mackerel, or sardine), cod liver oil is extracted specifically from the liver of Gadus morhua and related species, where the fat-soluble vitamins A and D that the animal synthesizes or stores accumulate; this distinct composition is what sets cod liver oil apart from conventional fish oils and what determines its particular clinical indications, its specific safety profile, and the dosing precautions it warrants.
The nutritional profile of cod liver oil combines three simultaneous contributions in physiologically significant amounts: approximately 1-1.5 grams of EPA+DHA per teaspoon (5 ml), about 4,500-10,000 IU of vitamin A (as retinol and retinyl esters, far more concentrated than in any conventional fish oil), and 400-1,200 IU of vitamin D (varying by product and manufacturer); this triple profile is what clinically differentiates it from other supplements.
The most famous historical indication is the prevention of childhood rickets, a disease caused by severe vitamin D deficiency during growth that produces characteristic bone deformities and was endemic in urban European children before the introduction of systematic supplements; today, cod liver oil remains relevant as a combined source of vitamin D and omega-3 at high latitudes with low winter sun exposure, although modern vitamin D3 supplements at known doses are a more controllable alternative.
The EPA+DHA supplied by cod liver oil has the classic cardiovascular effects of omega-3s: modest reductions in triglycerides, improvements in endothelial function, systemic anti-inflammatory effects, and slight reductions in blood pressure; the magnitudes are comparable to those of conventional fish oils at equivalent EPA+DHA doses.
In Scandinavian population studies, regular consumption of cod liver oil in childhood has been associated with a lower later incidence of type 1 diabetes and multiple sclerosis, probably because of the sustained supply of vitamin D during the development of the immune system; these data are observational and require confirmation in prospective trials, but they lend support to the traditional Scandinavian nutritional practice.
The traditional doses are 1 teaspoon (5 ml) or 1-2 capsules daily in adults; in children, 2.5-5 ml/day depending on age; commercial products vary enormously in their concentration of vitamins and omega-3s, and it is advisable to read the specifications of the specific product to calculate the actual intake; flavored products (with lemon or mint) are more palatable than traditional ones with a pure fish taste.
The most important precaution is to watch the total vitamin A intake to avoid chronic toxicity: high doses or prolonged use can cause hypervitaminosis A with headache, nausea, hair loss, liver toxicity, and, in children, benign intracranial hypertension; in pregnancy, high doses of vitamin A are teratogenic, and cod liver oil should be limited to the usual amounts consumed by the general population (one teaspoon daily is generally safe, but high doses or especially concentrated products should be avoided); people with chronic liver disease should avoid high doses; additional vitamin A or D supplements can lead to excessive intake if combined with cod liver oil; cheap products may be contaminated with heavy metals or PCBs in problematic amounts, so it is advisable to choose products with a purity certification (IFOS, Friend of the Sea); in breastfeeding it is considered safe at usual doses and provides omega-3s to the baby through the milk; in children it is a well-tolerated traditional option for ensuring vitamin D intake in winter at high latitudes.
Information, not medical advice. Scientific evidence reflects the quality of the studies.