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Updated 02 November 2015

Fish oil cuts blindness risk

Eating three or more portions of oily fish per week could reduce the risk of age-related macular degeneration (AMD) by 70 percent, says a new study from Australia.

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The results go against several recent reports that high dietary intakes of unsaturated fats, particularly mono- and poly-unsaturated fatty acids (MUFAs, PUFAs) could increase the risk of AMD, which have caused concern to both lay and medical communities.

“Our findings from a representative older population caution against altering current advice regarding dietary fat recommendations to the community,” wrote lead author Brian Chua from the University of Sydney.

AMD affects the central part of the retina called the macula, which controls fine vision, leaving sufferers with only limited sight. AMD affects over 30m people worldwide, and is the leading cause of blindness in people over 50.

How the study was done

The new study, published in the latest issue of Archives of Opthamology (Vol. 124, pp. 981-986), analysed the dietary intakes of 2258 older people in Sydney, Australia (average age 64).

Dietary intakes were measured using a 145-item self-administered food frequency questionnaire (FFQ), and further verified by 79 volunteers who completed four-day weighed food records on three separate occasions during the course of one year.

After five years of follow-up, the researchers calculated that people who ate at least one portion of fish every week could reduce their risk of developing early AMD by 40 percent.

People who ate three or more portions of fish per week reduced their risk of late AMD by 70 percent.

The results have implications for other populations since consumption of fish has seriously declined over the past 50 years in the UK. In the early 1950s mean consumption was around 230g per week, and it reached an all-time low of around 130g in the late 1970s. It has since recovered slightly, to just under 150g.

But it still remains that less than a third of adults presently eat any oily fish at all.

Oily fish most beneficial

When the Australian researchers calculated in terms of specific types of fats, they found that people with the lowest dietary intake of MUFA, omega-3 PUFA, especially alpha-linolenic acid, may be at increased risk of early development of AMD.

No relationship was found between nuts, butter and margarine intake and the risk of AMD.

The mechanism behind the benefits of oily fish was not studied by Chua, but the researchers propose that insufficient fatty acid intake could cause abnormal metabolism in the retina which affects cell renewal.

“Studies have shown that diets high in omega-3 fatty acids, particularly docosahexaenoic acid (DHA), derived largely from fish, may protect against retinal oxidation and degeneration,” they wrote.

Dr Frank Eperjesi, an expert in nutrition and eye health from Aston University in the UK told NutraIngredients.com that the explanation given by the scientists was highly plausible.

An excellent experimental design
Dr Eperjesi also noted that the study had been performed in a scientifically rigorous fashion with an excellent experimental design by a group that is well respected in this area of research.

"A problem often found with food frequency questionnaires is that the subjects' memory often fails them and they inappropriately report types and quantities of food consumed. This was checked by this group. They found that the food consumption reporting was accurate," he said.

The researchers plan to continue to study the same population, saying that further research using 10-year incident data would “provide greater study power to investigate any potential protective effects of long-chain omega-3 PUFA against the development of late AMD,” concluded the researchers.

They also called for future studies to collaborate and pool data to further examine dietary factors that affect the risk of AMD.

The risk of pollutants from oily fish, such a methyl mercury, dioxins, and polychlorinated biphenols (PCBs) have led to some claims to reduce fresh fish intake, especially for pregnant women who may damage the development of their babies.

Source: Decision News Media

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