More evidence against processed foods: MSG consumption increases glaucoma, cataract risk

Eating too much monosodium glutamate (MSG)—the flavor enhancer common in Asian and processed foods—could make you go blind.

Researchers at Hirosaki University in Japan have found that rats fed on diets high in MSG suffer vision loss and have thinner retinas. Glutamate, a group of chemicals that includes MSG, is an amino acid that acts as a neurotransmitter. It has already been shown to cause nerve damage in experiments where it is injected directly into the eye.

The researchers found high concentrations of MSG in the vitreous fluid, which bathes the retina. MSG binds to receptors on retinal cells, destroying them and causing secondary reactions that reduce the ability of the remaining cells to relay electrical signals. Lead researcher Hiroshi Ohguro noted that this is the first study to show that eye damage can be caused by eating food containing MSG. He said the findings might explain why in eastern Asia, there is a high rate of glaucoma.

In the study, rats were fed three different diets for six months, containing either high or moderate amounts of MSG, or none. In rats on the high-MSG diet, some retinal nerve layers thinned by as much as 75 percent. And tests that measured retinal response to light showed they could not see as well. Rats on the moderate diet also had damage, to a lesser extent.

MSG is used as a flavor enhancer in a variety of foods prepared in restaurants and by food processors. While technically MSG is only one of several forms of free glutamate used in foods, consumers frequently use the term MSG to mean all free glutamate.

Its use has become controversial in the past 30 years because of reports of adverse reactions in people who have eaten foods that contain MSG. According to the U.S. Food and Drug Administration (FDA), research on the role of glutamate in the nervous system has also raised questions about the chemical’s safety.

Peng Tee Khaw, a glaucoma specialist at Moorfields Eye Hospital in London, said “if you’re a sodium glutamate junky, then you could potentially run into problems with your retina.” Even if you’re not an MSG junky, researchers speculate that lower dietary intakes could produce the same effects over several decades.

Even if you’re not a fan of processed or Asian foods, there is still reason for concern. The use of glucocorticoids—anti-inflammatory drugs commonly prescribed for conditions such as asthma, rheumatoid arthritis and inflammatory bowel disease—is associated with increased susceptibility to cataracts and glaucoma.

Harvard researchers have also found that glutamate seems to be involved in the death of brain cells in Alzheimer’s victims. And high levels of it can result in a blocked brain artery, which often triggers stroke.