Thursday April 29 2010
Oily fish is rich in omega 3
“Fish oil supplements 'don't help the elderly',” the Daily Mail reported. It said a study has found that people aged 70 to 80 who took fish oil supplements for two years did not perform any better in memory and concentration tests than those who took a placebo.
This study followed 867 older adults who were cognitively healthy at the start of the study. Over two years, the cognitive performance of a group of people given fish oil was no different to that of a group given a placebo, and neither group showed significant decline in cognitive function. The participants already seemed to have reasonable intake of fish oils and were in good cognitive health, which could have limited the ability of the fish oil supplements to have an impact on cognitive performance.
The results of this study suggest that daily supplements of two different fatty acids (200mg of a fatty acid called EPA and 500mg of one called DHA) over two years in cognitively healthy older adults does not affect cognitive function. This does not rule out the possibility that taking supplements over a longer period might affect cognitive performance, or affect individuals who already have cognitive impairment.
Where did the story come from?
The research was carried out by Dr Alan D Dangour and colleagues from the London School of Hygiene and Tropical Medicine, and other hospitals and research centres in the UK and Australia. The study was funded by the UK Food Standards Agency, and service support costs were provided by NHS Research and Development. The work was published in the peer-reviewed American Journal of Clinical Nutrition.
The Daily Mail's coverage of this story was generally accurate.
What kind of research was this?
This randomised controlled trial (RCT) tested whether omega-3 (n-3) long-chain polyunsaturated fatty acid (LC PUFA) supplementation affected cognitive function in cognitively healthy older people. LC PUFAs are most commonly found in oily fish, and several (but not all) observational studies have suggested that higher consumption of fish is associated with improved cognitive performance and a reduced risk of dementia.
Observational studies into the effects of different nutrients should ideally lead to RCTs that scrutinise their findings more closely. RCTs reduce the risk of confounding factors affecting results, and give a clearer idea of the effects of the nutrient in question. This RCT had the added benefit of being double blinded, which means that neither the participants nor the researchers knew who was getting which treatment. This should mean that any preconceptions they may have had about the effects of the supplementation did not affect the performances in the tests of cognitive function.
What did the research involve?
The researchers recruited 867 adults, aged 70 to 79, who were cognitively healthy. Participants were recruited from 20 GP practices in England and Wales and were randomised to two groups between 2005 and 2006. People with diabetes or dementia, or those already using daily fish oil supplements, were not eligible to participate. Eligible individuals were assessed by a research nurse. Those who scored below an accepted limit on a standard cognitive test (MMSE score less than 24), indicating cognitive impairment, were also excluded. Participants completed a range of cognitive tests at the start and end of the study.
The participants were randomly assigned to receive either a fish oil supplement or a placebo supplement containing olive oil for the next two years.
The fish oil supplement consisted of LC PUFAs called eicosapentaenoic acid (EPA, 200mg) and docosahexaenoic acid (DHA, 500 mg). These levels were based on UK recommendations for oily fish consumption, typical dietary recommendations, and the recognised safe dose of n-3 LC-PUFAs. This dose is equivalent to eating about 1.75 portions of oily fish (250g) a week. Olive oil was chosen as a placebo as there are no reports that olive oil intake at these levels is associated with improved cognitive function. The fish oil pills and placebo looked identical and were both vanilla flavoured.
The researchers took blood samples from participants at the end of the study to measure their DHA and EPA levels and to confirm that the fish oil group had higher levels of these chemicals than the placebo group.
The researchers compared performance on the cognitive tests between the fish oil group and the placebo group. The analyses took into account the participants’ cognitive scores at the start of the study and their age, gender and age when they left full-time education.
What were the basic results?
The researchers were able to analyse data from 748 participants (86%) who completed the study.
Participants given fish oil pills were found to have higher levels of EPA and DHA in their blood. Based on a count of the leftover pills, adherence to taking the study medication was high (95% of capsules were taken in both groups).
Neither group showed a decline in cognitive function over the two years of the trial. There were no significant differences in cognitive performance during the trial between the fish oil group and the placebo group.
How did the researchers interpret the results?
The researchers concluded that there was no decline in cognitive function in either group over two years. They say that the lack of decline in cognitive function in the placebo group, and the short treatment period, could have limited their ability to detect an effect of fish oil on cognitive function.
This study used a robust design to assess the effects of these fish oils in cognitively healthy older people. It found no difference between n-3 LC PUFA supplementation (200mg of EPA plus 500mg of DHA daily) and a placebo (olive oil). There are some points to note:
- People who withdrew from the study had poorer cognitive performance at the start of the study than those who remained in it. This could have affected the results, although the drop-out rate was similar in both groups.
- It is possible that the participants were already consuming sufficient n-3 LC PUFAs. The researchers note that this is supported by the fact that sufficient DHA levels were found in the blood of the placebo group (with higher levels in the n-3 LC PUFA group). This could have reduced the potential effect of supplementation.
- The researchers suggest that the study may have been too short to detect an effect of fish oil supplementation on cognitive performance.
- Different results may be seen in older adults who already have mild cognitive impairment.
The results of this study suggest that daily supplementation with 200mg of EPA plus 500mg of DHA over two years in cognitively healthy older adults does not have an effect on cognitive function. This does not rule out the possibility that longer-term supplementation might affect cognitive performance, or affect individuals who are already cognitively impaired.