Cod Liver Oil is an oil taken from the liver of the cod fish and used as a nutritional supplement. It gives the body three things at once: omega-3 fatty acids called EPA and DHA (two types of omega-3 fat found in fish), vitamin A (also known as retinol), and vitamin D. Vitamin A supports the immune system, vision in dim light, and healthy skin. Vitamin D helps the body control calcium and phosphate for strong bones, teeth and muscles. Omega-3s help lower triglycerides, a type of fat in the blood. The amount of each nutrient differs from one Cod Liver Oil product to another, so reading the label matters.

Cod Liver Oil is different from ordinary fish oil. Fish oil mainly gives omega-3 fats. Cod Liver Oil also carries vitamins A and D, in amounts that vary from product to product. This mix is useful, but it also means that taking too much can build up these vitamins in the body.

Each part of Cod Liver Oil has its own job:

• Vitamin A helps your immune system fight illness and infection, helps you see in dim light, and keeps your skin and the lining of parts of the body, such as the nose, healthy. It also helps form and maintain healthy teeth, bones and soft tissue.
• Vitamin D helps the body absorb calcium from food. Calcium and phosphate are needed for healthy bones, teeth and muscles.
• Omega-3 fats (EPA and DHA) lower triglycerides in the blood.

People may be advised to take Cod Liver Oil when their diet does not give them enough of these nutrients. Anyone who already has heart disease or high triglycerides should ask their doctor whether a fish oil supplement suits them, rather than starting one on their own.

Because vitamins A and D can be harmful in large amounts, Cod Liver Oil needs some care. Health guidance advises that your total vitamin A from food and supplements together should not go above 1.5 mg a day, and that fish liver oil counts towards this total. Having more than this over many years may affect your bones. Too much vitamin D over a long time can raise calcium in the blood, which can weaken bones and damage the kidneys and heart.

Pregnancy needs special attention. NHS advice is not to take Cod Liver Oil or other vitamin A supplements while pregnant, because too much vitamin A can harm a baby's development. If you take other medicines, have a long-term health condition, or are planning a pregnancy, speak to your doctor or pharmacist before starting Cod Liver Oil.

Cod Liver Oil is used as a nutritional supplement. It is taken:

• As a source of omega-3 fats - It provides EPA and DHA, the omega-3 fats also found in seafood and oily fish.
• As a source of vitamin A - Fish liver oil is high in vitamin A, which the body needs for its defence against infection, for vision in dim light, and for healthy skin.
• As a source of vitamin D - Vitamin D helps the body regulate calcium and phosphate, which are needed for healthy bones, teeth and muscles.
• To help lower blood triglycerides - EPA and DHA lower triglycerides, a type of fat in the blood. If you have high triglycerides or heart disease, ask your doctor whether a fish oil supplement suits you. Do not take more than the label amount to lower triglycerides, because this also raises your vitamin A and D intake.

1. Three nutrients in one supplement - Cod Liver Oil provides omega-3 fats (EPA and DHA) along with vitamins A and D.
2. Supports bone, teeth and muscle health - The vitamin D in Cod Liver Oil helps regulate calcium and phosphate, which are needed for healthy bones, teeth and muscles.
3. Supports vision in dim light - Vitamin A helps your eyes see in low light.
4. Supports the immune system and skin - Vitamin A helps the body's natural defence against infection work properly and keeps skin and the lining of the nose healthy.
5. Helps lower blood triglycerides - A review of 23 studies found that EPA and DHA lower triglycerides by about 15 percent. Do not take more than the label amount of Cod Liver Oil for this, because higher doses also raise your vitamin A and D intake.

Common Side Effects (Usually Mild and may lessen with continued use)

• Fishy or unpleasant taste in the mouth
• Bad breath
• Burping
• Bad-smelling sweat
• Headache
• Heartburn
• Stomach pain or discomfort
• Nausea
• Diarrhoea or constipation
• A change in your sense of taste

Serious Side Effects (Seek Urgent Medical Attention)

These are usually linked to getting too much vitamin A or vitamin D, often from taking Cod Liver Oil along with other supplements.

• Hypervitaminosis A (vitamin A toxicity) - This means there is too much vitamin A in the body. Taking too many supplements is the most common cause. Signs include blurred vision, bone pain or swelling, headache, nausea and vomiting, and skin changes such as cracking at the corners of the mouth. In babies, it can cause softening of the skull bone and a bulging soft spot on the head. Left unchecked, it can lead to very high blood calcium, kidney damage and liver damage.
• Hypercalcaemia (too much calcium in the blood) - Taking too much vitamin D over a long time can cause calcium to build up. This can show up as nausea, vomiting, constipation, poor appetite, weakness, weight loss and confusion. It can weaken bones and damage the kidneys and heart, and may lead to kidney stones.

• Follow the directions on the product label or the advice of your doctor. Products differ in how much vitamin A and D they contain, so the amount in one brand may not match another.
• If you have capsules, swallow them whole with a glass of plain water. Do not crush, chew or break them unless the label says you can.
• If you have the liquid, measure it with the spoon or cup that comes with the pack rather than a kitchen spoon.
• You can link Cod Liver Oil to a regular meal to help you remember it. Whether you take it with food or without, keep it the same each day.
• Take it at about the same time every day so it becomes part of your routine.
• Do not take Cod Liver Oil together with other supplements that contain vitamin A or vitamin D unless your doctor has checked the combined amount.
• If your doctor has recommended Cod Liver Oil for a set period, keep taking it for that length of time and check back with them before stopping or changing how much you take.

Cod Liver Oil does not act like a single medicine. It works by topping up three nutrients that the body uses in different ways.

• Vitamin A (retinol) - Your eyes use vitamin A to see when light is low. The body also uses it to form and maintain skin, teeth, bones and the moist linings inside the body, such as the nose, and to help the immune system work properly. If you take more vitamin A than you need, the extra can build up in the body, which is why too much can cause problems.
• Vitamin D - Vitamin D helps your gut take in calcium from food. It also helps the body keep the right balance of calcium and phosphate, two minerals that make bones and teeth hard and help muscles work.
• Omega-3 fats (EPA and DHA) - These are a kind of fat found in seafood and fish oil. They seem to work by reducing the amount of triglycerides and other fats that the liver makes.

• Read the label to see how much vitamin A and vitamin D each dose of Cod Liver Oil contains.
• Add up vitamin A and D from all your supplements, including multivitamins, before taking Cod Liver Oil.
• If you are pregnant or trying for a baby, choose a supplement without vitamin A unless your doctor says otherwise.
• If you eat liver once a week, skip supplements that contain vitamin A, including Cod Liver Oil.
• Take Cod Liver Oil at the same time each day, such as with the same meal, so you do not miss or repeat a dose.
• Tell your doctor if you are allergic to fish or shellfish before starting.
• Mention Cod Liver Oil to every doctor and pharmacist you see, especially before starting a new medicine.

• Keep Cod Liver Oil in the container it came in, with the lid tightly closed.
• Store it at room temperature, away from excess heat and moisture. Follow any storage temperature printed on your product's label.
• Keep it out of the reach of children and pets. Babies and children are more sensitive to smaller amounts of vitamin A.

• Liver and liver products - Liver is very high in vitamin A. If you eat liver once a week, NHS advice is not to take supplements containing vitamin A, including fish liver oil.
• Other vitamin A-rich foods and fortified foods - Foods such as eggs, cheese, oily fish, and fortified spreads, milk and yoghurt also provide vitamin A. Your total from food and supplements together should stay at or below 1.5 mg a day.
• Oily fish - Oily fish such as salmon, sardines, mackerel and trout also give omega-3 fats and vitamin D. Girls, women who are planning a pregnancy or may have a baby one day, and women who are pregnant or breastfeeding are advised to have no more than 2 portions of oily fish a week, because pollutants in oily fish can build up in the body and affect a baby's development in the womb.
• Alcohol - Ask your doctor whether it is safe for you to drink alcohol while taking Cod Liver Oil.

• Isotretinoin (acne medicine) - Isotretinoin is related to vitamin A. NHS advice lists vitamin A supplements and supplements that contain vitamin A among the things that do not mix well with it, so avoid Cod Liver Oil while taking isotretinoin unless your doctor says otherwise.
• Other vitamin A or vitamin D supplements and multivitamins - Taking these together with Cod Liver Oil can push your total intake too high and raise the risk of vitamin A or vitamin D toxicity.
• Orlistat (weight-loss medicine) - Orlistat stops some fat in food from being absorbed, which can also reduce absorption of fat-soluble vitamins such as A and D. Vitamins are usually taken at a different time from orlistat. Ask your doctor or pharmacist how to space Cod Liver Oil and orlistat.
• Warfarin (blood thinner) - Tell your doctor about all vitamins and supplements, including Cod Liver Oil, before or while taking warfarin.
• Other prescription medicines - Tell your doctor and pharmacist about all medicines, vitamins and herbal products you take. They may need to change doses or check you more closely for side effects.

• Kidney disease - Too much vitamin D can raise blood calcium and damage the kidneys. Tell your doctor if you have kidney disease before taking Cod Liver Oil.
• High blood calcium or overactive parathyroid glands (hyperparathyroidism) - The vitamin D in Cod Liver Oil can raise calcium further. Speak to your doctor first.
• Liver disease - Tell your doctor if you have liver disease. Excess vitamin A can damage the liver.
• Weak bones (osteoporosis) - Long-term vitamin A intake above 1.5 mg a day may affect bones. Women past the menopause and older men should stay within this limit.
• Irregular heartbeat (atrial fibrillation or atrial flutter) - Tell your doctor if you have one of these heart rhythm problems before taking omega-3 products.
• Diabetes, thyroid disease or pancreatic disease - Tell your doctor about these conditions before taking omega-3 products such as Cod Liver Oil.
• Fish or shellfish allergy - Tell your doctor if you are allergic to fish or shellfish before starting Cod Liver Oil.
• Pregnancy or planning a pregnancy - Avoid Cod Liver Oil unless your doctor advises otherwise, because of its vitamin A content.

There is no single dose that fits every Cod Liver Oil product, because the amounts of vitamin A and vitamin D vary between brands. Use the amount printed on your product label, or the amount your doctor has advised, and do not take more.

NHS guidance sets these upper limits for total daily intake, counting food and all supplements together:

• Vitamin A - no more than 1.5 mg (1,500 micrograms) a day for adults.
• Vitamin D - no more than 100 micrograms (4,000 IU) a day for adults and children aged 11 to 17, no more than 50 micrograms (2,000 IU) a day for children aged 1 to 10, and no more than 25 micrograms (1,000 IU) a day for babies under 12 months.

Always follow the dose your doctor prescribes.

Taking too much Cod Liver Oil, especially over weeks or months or alongside other vitamin supplements, can lead to vitamin A or vitamin D toxicity.

Signs of too much vitamin A (hypervitaminosis A) include:

• Blurred vision
• Headache
• Nausea and vomiting
• Bone pain or swelling
• Cracking skin at the corners of the mouth
• In babies, a bulging soft spot on the head

Signs of too much vitamin D (high blood calcium) include:

• Nausea, vomiting and constipation
• Poor appetite and weight loss
• Weakness
• Confusion

If you think you or a child has taken too much, stop Cod Liver Oil and contact a doctor or go to the nearest emergency department straight away. Take the pack with you. For too much vitamin A, treatment usually involves stopping supplements that contain vitamin A, and most people recover fully.

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed one and carry on with your usual schedule. Do not take a double dose to make up for the one you missed, because extra doses add to your vitamin A and vitamin D intake.

Contact your doctor straight away, or get emergency help, if you notice:

• Blurred vision or a severe headache
• Bone pain or swelling
• Ongoing nausea or vomiting
• Cracking at the corners of the mouth or other new skin changes
• Constipation, poor appetite, weight loss, weakness or confusion that does not go away
• A bulging soft spot on a baby's head, or a baby who is not gaining weight, if Cod Liver Oil has been given to an infant
• Any sign of an allergic reaction if you have a fish or shellfish allergy
• You find out you are pregnant while taking Cod Liver Oil