Fish oil supplements do not seem to improve the heart health of people who are ill or prevent dementia in healthy older people, two new studies suggest.

Omega-3 fatty acid supplements — tasteless, odourless powder that usually consists of purified fish oil from sardines and anchovies — have offered the promise of health benefits.

Eating one portion of oily fish a week might be a better option than turning to supplements. (Carlos Barria/Reuters)

Research has hinted that omega-3 fatty acids may be involved in keeping the brain's nerve cells healthy with age, but there's been little proof of whether they actually prevent cognitive decline and dementia.

This week's issue of the Cochrane Database of Systematic Reviews includes a comparison of three high-quality trials of more than 3,500 participants, comparing the effects of omega-3 fatty acids taken in capsules or margarine spread to those of sunflower oil, olive oil or regular margarine.

"The results of the available studies show no benefit for cognitive function with omega-3 polyunsaturated fatty acid supplementation among cognitively healthy older people," Emma Sydenham at the London School of Hygiene & Tropical Medicine and her co-authors concluded.

"Omega-3 may have other health benefits," they said in noting fish form an important part of a healthy diet.

"We would still support the recommendation to eat two portions a week, including one portion of oily fish," said study co-author Alan Dangour, a nutritionist at the British postgraduate institute.

Despite the large number of participants, none of the studies lasted long enough to see changes in cognitive function including memory and verbal fluency among those over the age of 60, the reviewers cautioned.

They called for longer-term studies.

Heart benefits not apparent

Tuesday's issue of the New England Journal of Medicine includes a Canadian study that concluded omega-3 supplements showed no benefits in reducing death and disease rates among people with high blood sugar or diabetes who had had previous heart attacks, strokes or other heart problems.

Lead investigator Jackie Bosch of McMaster University in Hamilton and her colleagues randomly assigned participants to receive either a placebo or one gram of purified, prescription fish oil that contained the omega-3 fatty acids.

The 6,281 patients who got fish oil were no more or less likely to die from cardiovascular causes than the 6,255 who took sugar pills.

There were also no differences in heart attacks, strokes, hospitalizations for heart problems, stent procedures or chest pain between the two groups.

Adverse events were similar.

The dose was less than commonly prescribed and it's still possible that the supplements could help healthier people, though that wasn't investigated in this study.

The study, called ORIGIN, was designed as a diabetes trial, and the results were also presented at the American Diabetes Association’s conference in Philadelphia.

That research was sponsored by Sanofi.