Nothing fishy about taking cod liver oil
The Irish Times
Health Supplement, p. 13
3 March 2009
DOES IT WORK? Recent studies have found omega-3 fatty acids yield consistent health benefits
COD LIVER OIL is a well-known food supplement and one that many may remember from their childhood. Many were raised on spoonfuls of the oil that could taste and smell anything from mildly fishy to downright disgusting.
Today, the oil is more usually taken within gelatin capsules, though some can be so big they are a challenge to swallow. Hence the question that was put to me: is it really worth taking cod liver oil just because someone in the family believes in it?
Cod liver oil is one of several oils made from fish. Fish oil is extracted from the whole body of cooked oily fish, such as mackerel, herring, sardines and salmon. The rest of the fish is used to make fish meal.
The livers of cod are removed, cooked by steaming and then the oil extracted by pressing. Cod liver oil and fish oils contain large amounts of omega-3 fatty acids, but cod liver oil also contains significant amounts of vitamins A and D.
Evidence from studies
Fish oils came to prominence in the 1970s when studies reported that Inuit Eskimos had a lower risk of heart disease and much higher fish consumption. More recent studies have examined data from 36 countries and found significant associations between fish intake and lower risk of death from heart disease.
Randomised, controlled trials were then conducted with people taking cod liver oil or fish oil compared with those taking placebos or plant oils. Several controlled studies reveal a consistent pattern of fish oils reducing the risk of heart attack and other forms of cardiovascular disease. Curiously, omega-3 fatty acids from plants (such as flaxseed and walnuts) do not have the same protective effects against heart disease, although they have other benefits.
Cod liver oil for arthritis also has a long history. An article from the London Medical Journal in 1783 described patients with long-standing arthritis pain finding relief from several tablespoonfuls of cod liver oil per day. At that time, the relief was believed to be due to people “oiling their joints”. Recent research has demonstrated more plausible mechanisms by which the oil benefits arthritic joints.
The omega-3 fatty acids are required by our bodies to make several biochemicals involved in inflammation. Without these existing in proper proportions, inflammatory diseases like arthritis can develop.
Early clinical studies of cod liver oil produced inconsistent results in arthritis patients. More recent studies revealed consistent benefits with morning stiffness, joint pain and grip strength.
Very recently, cod liver oil has been recommended to prevent Alzheimer’s disease. This connection probably developed because omega-3 fatty acids make up about one third of the fats found in the brain’s grey matter. Very little research has been conducted in this area, but a few studies have found no beneficial effects from cod liver oil for patients with mild to moderate Alzheimer’s.
The most common adverse effects of cod liver oil are gastro-intestinal, especially when more than one tablespoonful of oil (3 grams of omega-3 fatty acids) is taken daily. These effects include fishy breath odour, belching, nausea and vomiting.
Some concerns have been expressed about cod liver oil containing excessive amounts of vitamins A and D. One tablespoonful of cod liver oil provides about 12,000 IU vitamin A and 1,200 IU vitamin D. This is a little more than what is usually recommended in daily allowances, but well within safe ranges. Problems are unlikely to arise unless several tablespoonfuls were taken daily for extended periods. Anyone with concerns, or taking other vitamins, should consult a GP or pharmacist.
Our bodies require different types of fatty acids. Omega-6 fatty acids are found mostly in vegetable oils, and Western diets now tend to include 20 to 30 times more omega-6 fatty acids than omega-3 ones. A more balanced intake of omega-3 and omega-6 fatty acids is needed, which is why many dietary recommendations now include a couple of portions of oily fish. While we may not want to return to the days of tablespoonfuls of terrible-tasting cod liver oil, many could benefit from a capsule a day or a couple of portions per week of omega-3-rich fish.