Is it time for pharmacists to stop recommending the supplement, asks Rod Tucker
Ingestion of cod liver oil has a long history and was even used by the Vikings during the cold months. The medicinal use of cod liver oil is attributed to Dr Darbey in Manchester in 1789. Darbey described the case of a woman with excruciating rheumatism who was applying the oil to her joints and, after deciding to take it orally, was pain free within a few weeks.
Cod liver oil is high in the omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) and is also a good source of vitamins A and D. The purported health benefits of cod liver oil include positive effects on the heart, brain and joints. But how robust is the evidence upon which these claims are based?
The omega-3 fatty acids are able to reduce various inflammatory markers such as C-reactive protein and studies suggest that consumption of fish oils can lead to a reduction in blood pressure, triglycerides, augment endothelial function and improve the cardiovascular risk profile in those with metabolic syndrome.
Much of these claims originate from work in the 1970s, when it was discovered that the incidence of cardiovascular disease was rare among Inuits in Greenland. It was thought that this was primarily due to their high intake of marine oils from eating fish. However, recent studies have found that the changes in cardiovascular risk do not translate into actual benefits.
Fish oils had no effect on heart-related deaths or strokes, did not reduce cardiovascular mortality in those with multiple risk factors or have any noticeable effect in secondary prevention. Moreover, the most recent review of trials with fish oil supplements found no benefit in heart disease or major vascular events.
Feeding our brains
As omega-3 oils are an important constituent of our brains, increased consumption may help reduce cognitive decline that can lead to dementia and there is some evidence that lower levels of DHA are associated with smaller brain volumes and a pattern of cognitive impairment. However, a recent review of trials in patients with mild to moderate Alzheimer’s disease, the most common form of dementia, found no evidence of benefit from fish oils on cognition, everyday function, quality of life or mental health.
There has been great interest in the potential for cod liver oil to reduce the aches and pains associated with rheumatoid and osteoarthritis. The latest systematic review on the use of fish oils for arthritic pain, concluded that these oils had only a moderate effect at reducing pain in those with rheumatoid arthritis. The effect on osteoarthritic pain was negligible and small for other forms of arthritis.
There is scant evidence for the other supposed health benefits of cod liver oil such as asthma and weight loss and so perhaps we should just stick with the recommendation to eat fish at least twice a week and not waste our money supplementing with cod liver oil.