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Wednesday, 23 October, 2002, 18:02 GMT 19:02 UK
Food additives 'affect sight'
Chinese food
The food additive MSG is found in Chinese food
Scientists are warning that a flavouring, commonly found in Chinese food, could be linked to sight problems.

Tests in rats have shown that high levels of monosodium glutamate (MSG) can damage the retina.

MSG is found in oriental and processed foods.

The research was carried out by scientists at Hirosaki University in Japan.

They found rats fed on diets high in MSG suffered vision loss and had thinner retinas.


If you have the odd take-away, I shouldn't worry

Professor Peng Tee Khaw, Moorfields Eye Hospital
But UK eye experts said people would have to eat an exceptionally large amount of MSG before they suffered problems, and eating a take-away once a week would not cause problems.

The researchers theory of how MSG affects sight is that it binds to receptors on retinal cells, destroying them.

This then triggers secondary reactions that reduce the ability of the cells which are left to relay electrical signals.

Concentrations

The Japanese team fed rats three different diets for six months, with either high or moderate amounts of MSG, or none.

MSG made up 20% of the diet of the rats given the highest amount.

In rats on the high MSG diet, some retinal nerve layers thinned by as much as 75%.

They were also unable to see natural light as well.

Some damage was also seen in rats put on the moderate MSG diet.

Researchers also found high concentrations of MSG in the vitreous fluid which bathes the retina.

The research was published in New Scientist magazine and the journal Experimental Eye Research.

'Theoretically possible'

Lead researcher Hiroshi Ohguro said it was the first study to show eating food containing MSG could cause danage to the eyes.

He told New Scientist high levels of MSG had been used in the tests.

But he added: "Lesser amounts should be OK, but the precise borderline amount is still unknown."

He suggested the study could explain why there is a high level of normal-tension glaucoma in eastern Asia.

Normal-tension glaucoma is a form of the disease which leads to blindness without the usual increase in pressure inside the eyeball.

However, the higher rate could also be due to genetics.

Peng Tee Khaw, professor of glaucoma and wound healing at Moorfields Eye Hospital in London, told BBC News Online the rats were fed a huge amount of MSG.

He said they were given an amount equal to a salt cellar half their size, so humans would have to eat an equivalent amount.

Professor Khaw said: "It's theoretically possible that if people ate large amounts of this stuff, they would have a damaging effect.

"But once a week, it would be a miniscule amount in comparison with what these researches are putting into these rats.

"If you have the odd take-away, I shouldn't worry."

He said if people should perhaps be careful if they did have extremely high amounts of MSG in their diets, or had pre-existing retinal problems.

See also:

13 Apr 02 | Health
06 Oct 99 | Medical notes
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