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13-06-2012 | Article

Fish oil health claims don't hold water


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MedWire News: Fish oil flounders in attempts to improve cognitive function among older adults or prevent cardiovascular events among high-risk patients, two new studies suggest.

Although evidence from observational studies has hinted that the fish-oil components omega-3 long-chain polyunsaturated fatty acids (PUFAs) have a beneficial effect on cognitive function, a review of data from three randomized trials suggests otherwise, write Emma Sydenham (London School of Hygiene and Tropical Medicine, London, UK) and colleagues.

"Direct evidence on the effect of omega-3 PUFA on incident dementia is lacking. The available trials showed no benefit of omega-3 PUFA supplementation on cognitive function in cognitively healthy older people," they write in a report from The Cochrane Library.

The authors looked at three studies in which participants received omega-3 PUFA in capsules or in a margarine spread, while controls received olive or sunflower oils or a conventional margarine. Two of the studies focused on cognitive health, and one looked at cognitive function as a secondary outcome.

In two of the studies, including a total of 3221 participants, there were no differences between fish oil consumers and controls in Mini-Mental State Examinations at either 24 or 40 months of follow-up. Similarly, there were no significant differences between the intervention group and controls among 1043 participants of two studies in word learning, digit span, verbal fluency, or other tests of cognitive function.

"Further studies of longer duration are required. Longer-term studies may identify greater change in cognitive function in study participants which may enhance the ability to detect the possible effects of omega-3 PUFA supplementation in preventing cognitive decline in older people," Sydenham et al write.

In a second study, Jackie Bosch (McMaster University, Hamilton, Ontario, Canada) and colleagues evaluated the ability of an omega-3 PUFA capsule to prevent cardiovascular events in 12,535 patients with diabetes who were enrolled in a clinical trial of a long-acting insulin.

There were no significant differences in the primary outcome of death from cardiovascular causes between patients in the intervention group or controls (9.1 vs 9.3%, hazard ratio= 0.98). No associations were found between mega-3 PUFA use and other endpoints, including major vascular events, death from any cause, or death from arrhythmia. Adverse events were similar between the groups.

"Whether similar results would have been observed at higher doses is unknown. Furthermore, these findings may not be relevant to dietary recommendations to consume more fish, because dietary change not only increases the intake of foods containing n-3 fatty acids but is also associated with a reduction in the consumption of foods such as red meats, which may be harmful," write Bosch et al in the New England Journal of Medicine.

By Neil Osterweil