Could myopia be related to too much MSG?

The myopia epidemic in school children

There has been a big increase in myopia – or short-sightedness – in the last 40 years, particularly in East and South-East Asia. In some Chinese cities, up to 90 per cent of recent high school graduates have myopia and up to 20  per cent  have high myopia.

It’s not just the inconvenience of wearing glasses. High myopia increases the risk of blindness due to retinal detachment, glaucoma or myopic macular degeneration. 

BLOGmsg01  The Conversation https://theconversation.com/short-sightedness-in-kids-was-rising-long-before-they-took-to-the-screens-122530

Latest studies suggest that the epidemic is due to near work - whether reading from books or screens - and not enough outdoor time (1,2).

But none of these studies looked at diet.

Could myopia be caused by too much MSG?

BLOGmsg02   New Scientist https://www.newscientist.com/article/dn2957-too-much-msg-could-cause-blindness/

Researchers at Hirosaki University in Japan (5) found that rats fed on diets high in MSG suffered vision loss and had thinner retinas. Glutamate had already been shown to cause nerve damage when injected directly into the eye (3) but this was the first study to show that eye damage could be caused by eating food containing MSG.

In the study led by Hiroshi Ohguro, rats were fed three different diets for six months, containing zero, moderate, or high amounts of MSG. In rats on the high-MSG diet, some retinal nerve layers thinned by as much as 75 per cent, and tests showed they could not see as well. Rats on the moderate diet had similar damage to a lesser extent.

While the amount of glutamate in the rats’ diets was extremely high, lower dietary intakes could potentially produce the same effects over several decades. The researchers concluded:

“The present study suggests that a diet with excess sodium glutamate over a period of several years may increase glutamate concentrations in vitreous and may cause retinal cell destruction.”



BLOGmsg03   Food Navigator https://www.foodnavigator.com/Article/2002/10/25/Eye-damage-from-MSG-consumption

A food industry response to the study:  “With such persuasive evidence it is clear that food processors must brace themselves for another wave of anti-MSG activity from global consumer associations.” (6)

How to avoid MSG

*flavoured chips and snacks
*instant noodles and snacks with flavour sachets
*crackers with flavours such as pizza or chicken, even some 'plain' rice crackers
*soups, sauces - canned, packet, bottled, restaurant
*stock cubes, stocks
*gravy, gravy mix
*salad dressing
*crumbing mixes
*seasoned salt
*ready meals
*slimmers or lite products
*always check ”healthy” foods such as rice crackers in the health food aisle
*frozen foods and meals
*pies, party pies, sausage rolls
*fresh sausages, marinated meats, stuffed or seasoned chicken
*bottled soy or oriental sauces
*deli meats such as devon, some hams, luncheon chicken, turkey
*chicken nuggets
*flavoured tuna
*vegetarian “meats”/burgers/sausages
*BBQ chicken
*takeaways

See our shopping list for some MSG-free snacks and foods

References

1. Mackey, D, Shortsightedness in kids was rising long before they took to the screens, The Conversation, 7th January 2020, https://theconversation.com/short-sightedness-in-kids-was-rising-long-before-they-took-to-the-screens-122530

2. HE M et al, Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China: A Randomized Clinical Trial , JAMA, 2015;314(11):1142-8. https://jamanetwork.com/journals/jama/fullarticle/2441261

3. Samuels A, Retinal Degeneration, Truth in Labeling Campaign, https://www.truthinlabeling.org/retinal.html accessed 31/01/2020

4. Graham-Rowe D, Too much MSG could cause blindness, New Scientist, 26/10/2002, https://www.newscientist.com/article/dn2957-too-much-msg-could-cause-blindness/, accessed 31/10/2020

5. Ohguro H et al, A high dietary intake of sodium glutamate as flavoring (ajinomoto) causes gross changes in retinal morphology and function. Exp Eye Res. 2002 Sep;75(3):307-15. https://www.ncbi.nlm.nih.gov/pubmed/12384093

6. Food Navigator, Eye damage from MSG consumption, 24/10/2002 last updated 18/07/2008, https://www.foodnavigator.com/Article/2002/10/25/Eye-damage-from-MSG-consumption, accessed 31/01/2020 
 
More info

MSG factsheet

Introduction to the side-effects of food