The experts reveal everything you need to know about the supplement that can fight heart disease, ease arthritis - and even stave off blindness.
All fish oils contain omega-3s, types of polyunsaturated fatty acid which are essential for health.
Fish such as mackerel, salmon, trout, sardines, pilchards and fresh tuna, which are known as oily fish, are the richest sources.
Dr Carrie Ruxton, nutritionist for the Health Supplements Information Service, says: 'There are different types of omega-3 fatty acids, but the key health benefits are believed to come from the very long chain omega-3s, called docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA].'
The Food Standards Agency (FSA) recommends we eat a minimum of two portions of fish each week, one of which should be an oily fish (one portion is about 140g). This provides a daily intake of 450mg of EPA and DHA.
Today many supplements will specify which type they contain and in what concentration.
EPA and DHA have different roles in the body. Dr Ruxton says: 'Studies suggest DHA is more important for the brain, retina and infant development, while EPA is more important for vascular health [blood vessels].'
'The difficulty we have in the UK is that two-thirds of people don't eat oily fish,' she says. 'The main source of long chain omega-3s in the diet is oily fish, and if we can't get them from that, we need to consider a supplement to top up our diet.'