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Q1: There are a bewildering number of fish oil capsules on the market ranging from cheap to expensive. How do you choose a product that has a high omega3 content and what is the daily recommended dose? I usually buy the Holland & Barrett EPA fish oil capsules which states on the label that they are "high in omega3 fatty acids" but I'm not sure how high is high. Name and address withheld.

A1: This reader has raised an important point. Most doctors tend to say that people should have an adequate amount of fish oil, very often they suggest a minimum of two oily fish meals, rich in omega3 a week. Others talk of having a desert spoon of fish oil or a couple of capsules a day but don't, as you say, specify the amount of omega3 that this will include. Omega3 and omega6 are known as the essential fatty acids (EFA). The correct balance between the two is needed. Most people have enough omega6 from the cereals in a normal diet. It is the omega3 that is usually in short supply.

The official answer to your question is that no definite figures can be given to the required daily intake because everybody's overall diet varies so much, and furthermore the way they metabolise omega3 and omega6 differs from individual to individual. Another factor is that at different times in someone's life the need for omega3 changes. Seven Seas, a reputable company, suggest that we should take 120 mgs a day of omega3 - of which EPA and DHA are two of its constituents and should be 83.2 mgs. This is contained in one of their One a Day cod liver oil capsules.

On the other hand Efalex made by Efamol, also a reputable company, contains both omega3 and omega6 in the correct proportions. Their suggestion is that the daily intake of omega3 should be 365 mgs of which DHA should compose 260 mgs and EPA 60 mgs. To achieve this daily dose of omega3 four capsules of Efalex need to be taken daily. Efamol produce tablets of varying strength and constituents in order to cater for different needs. For example there are preparations for the pregnant woman, cantankerous grandfather or troublesome teenager. Efamarine provides a mixture of fish oil, rich in omega3, and Primrose oil rich in omega6 in the correct proportions for everyday life, the fish oil provides the omega3 and the Primrose oil contributes 360 mgs of omega6.

Q2: My understanding is that EPA and DHA are only two of the components of omega3. If a food shows omega3 in the ingredients list, but not EPA and DHA, is it fair to assume that it doesn't contain these two components? If so, some food suppliers appear to be trading on the beneficial effects of omega3 when their products don't actually contain the beneficial components. Peter Kay, London.

A2: Omega3 contains DHA, docosahexaenoic acid, and EPA eicosapentaenoic. Omega3 and omega6, linoleic acid, are both polyunsaturated fats but omega3 can be regarded as a super unsaturated fat whereas omega6 is a standard unsaturated fat. The omega description of these essential fatty acids refers to the chemical nature of the fat and the position of the carbon bonding in the chemical structure of the compound.

Apart from the omega3 other constituents are present in fish oil. If possible it is always as well to take additional fibre with the omega3 together with a good all round multi vitamin and trace element supplement.

Q3: My 25-year-old son was diagnosed with epilepsy at ten years of age. He only has about one seizure a year. He takes a combination of Epilim (2000mg) and Lamotrigine(300mg) per day. He is also dyslexic. At the age of 19 he was diagnosed with MS, and takes no medication for this. Despite all this he is well and leads a normal life. Would omega3 help any of his conditions at his age and more importantly would it interfere with his epilepsy medication? Pat Percival, address withheld.

A3: There is no reason why someone taking anti epileptic treatment should not have an omega3 supplement. There has been a great deal of discussion about a possible role for omega3 therapy in multiple sclerosis but although it is unlikely to be curative it is sometimes recommended as a suitable supplement together with vitamin E, selenium and the B group of vitamins.

Q4: I would like to take omega3 fish oils, but I regularly take a daily vitamin and mineral supplement which contains, as most general supplements do, 5 micrograms of vitamin D. I understand that too much vitamin D is not desirable, but I have never seen the link made between omega3 and vitamin D, nor what the maximum daily amount of the vitamin is. I should be grateful for your comments on this. I am female and in my early 70s. Janet Biggs, address withheld.