Cod liver oil and fish liver oil: vitamin A content, pregnancy and omega-3 questions

Cod liver oil is pressed from cod liver, a store of vitamins A and D. Other fish liver oils, including halibut and shark liver oil, are similar. Fish body oil, krill oil and algal oil capsules supply omega-3 fats without being liver derived. Marketing often blurs them under the phrase omega-3, but the vitamin content is the key difference in safety.

The NHS notes in its vitamin A guidance that fish liver oil supplements are high in vitamin A. Because vitamin A is stored in the body, daily surplus builds up. The NHS advises that on average people should not have more than 1.5mg a day from food and supplements combined, because over many years this may weaken bones and increase fracture risk. Someone who also eats liver regularly, takes a multivitamin with vitamin A, or uses a cod liver oil capsule can exceed that limit without realising.

People at higher risk of osteoporosis, such as postmenopausal women and older men, are advised to be most careful.

NHS pregnancy advice is direct: do not take cod liver oil or supplements containing vitamin A, and avoid liver and liver products. The risk relates to retinol during early pregnancy, and the NHS Best Start in Life guidance names fish liver oil alongside liver as foods to avoid. If you want omega-3 in pregnancy, the NHS fish guidance suggests eating oily fish within its weekly limits rather than using liver oil.

Women who are planning pregnancy are generally advised to follow the same approach, because the vitamin is stored and early pregnancy often goes unnoticed.

People take cod liver oil for joints, mood, heart health, skin and as a source of vitamin D. The evidence varies by claim. Long-chain omega-3 fats from oily fish are linked with heart health in the NHS guidance, but that statement concerns fish in the diet, not liver oil capsules. Vitamin D is advised for many people in autumn and winter, but a dedicated vitamin D product delivers a known amount without the vitamin A load.

• For vitamin D, choose a vitamin D supplement rather than relying on liver oil.

• For omega-3, consider oily fish such as salmon or sardines within the NHS weekly advice.

• For joints or mood, discuss persistent symptoms with a GP rather than self-treating with high doses.

Liquid cod liver oil has been a traditional children’s remedy, but the vitamin content is high enough that doses must follow the label and the child’s age. UK routine advice for young children centres on dedicated vitamin A, C and D drops. Older adults on several supplements should total the vitamin A from all sources.

High vitamin A intake alongside prescription retinoid medicines is a concern because effects can add together. Omega-3 oils may affect bleeding slightly at high doses, so people on anticoagulants should check with an anticoagulant clinic or pharmacist. Allergy to fish is a reason to avoid fish oils unless an allergist agrees.