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PRI's Environmental News Magazine

Myopia

Air Date: Week of May 3, 2002

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Host Steve Curwood speaks with evolutionary biologist Loren Cordain. Cordain's recent paper suggests that diets high in starchy food may lead to near-sightedness.

Transcript

CURWOOD: Cereal, bread and sugar. These foods are staples of most diets. But a new theory suggests that eating them as a child can make you near-sighted. According to Loren Cordain, sugars and grains kick off a series of events in the body that can affect eye growth and lead to myopia. Dr. Cordain is an evolutionary biologist at Colorado State University. He studies paleo-diets—in other words, how ancient people used to eat. He’s also the author of a just-published paper that explains his theory about near-sightedness. Hello, sir.

CORDAIN: Hello.

CURWOOD: So, let’s get to your theory. I’m a child and I’m eating lots of white bread and candy. What could happen to my body that might lead to myopia?

CORDAIN: Well, we believe that when you eat lots of white bread and candy, these are what are called high-glycemic foods and they tend to elevate your blood sugar and your insulin levels. The elevation in insulin also causes an elevation of other hormones that regulate growth. And remember, myopia is a situation of uncontrolled growth.

CURWOOD: What’s the problem with the eye growing? You would expect an eye to grow as the child develops.

CORDAIN: You need to match the power of the cornea and the lens—which actually focus vision on the retina—you need to match the power of the cornea and lens to a growing eyeball. And so there has to be this dance; there has to be this coordination between the length of the eyeball and the focal power of the cornea and the lens. The hormonal signal that causes that is a substance called retinoic acid, and this chronically elevated level of insulin disrupts the retinoic acid signals.

CURWOOD: Let me be sure I understand what you’re saying here. The culprit here is not just sugar, but starchy food, in general, anything that raises insulin levels in the body?

CORDAIN: That’s right. Nutritionists have come up with a scheme of things which we call the glycemic index and we can rate how much a certain food elevates your blood sugar level. The higher the glycemic index, the more it raises blood insulin levels. Cereal grains. Virtually all cereal grains tend to have a high glycemic index.

CURWOOD: Now, it’s generally accepted that genetics and looking at things up close causes myopia. Your paper even mentions a study that shows that people began to get
myopia—that is, near-sightedness—after they started learning to read at an early age. How correct is this assessment of the problem of myopia?

CORDAIN: I think the thing is, when you look at reading, per se, is if reading should cause myopia, then the percentage of myopia in all populations that read ought to be somewhat similar. But the problem is, is that rural people— and there’s been a study done of rural people in a Pacific island— people don’t eat refined carbohydrates. They don’t have access to them. Yet, they have mandatory schooling. The children are required to read eight hours a day. These children, again, do not develop myopia— a less than two percent incidence rate— however, they’re reading for eight hours a day.

CURWOOD: Now, certainly lots of people who eat starchy diets have perfectly fine sight. Tell me, how significant a role do you think diet does play in myopia?

CORDAIN: Well, myopia results from the interaction of the environment and the genes. And there is no single gene that is responsible for myopia, there are multiple genes. And what we believe is that people who are genetically susceptible to insulin resistance are those that are most likely to develop myopia.

CURWOOD: Your paper isn’t new research, in the sense that you’ve gone out and conducted your own studies. Rather, it’s a review of other studies that have been published. And we spent some time talking with an ophthalmologist, who was recommended to us by the American Academy of Ophthalmology, and he found your study intriguing, but he said he wanted to see more original research. How do you respond to that?

CORDAIN: Well, I would agree with him entirely. I mean, what our group has done that is original research is we’ve put together all the pieces of the puzzle and that’s probably why you’re interviewing me now. How in the world can diet have anything to do with myopia? Because most people don’t have a clue of this entire metabolic cascade. That kind of information’s only been out there for a very short period of time and the idea that retinoic acid is the chemical messenger for myopia is only about a year or two old, as well.

CURWOOD: Loren Cordain is a biologist at Colorado State University. Thanks for taking this time with us.

CORDAIN: Well thank you. It’s been my pleasure.

CURWOOD: For more information on Loren Cordain’s research and for a discussion about his book on the dangers of high starch diets, visit our website at www.loe.org. That’s www.loe.org.

[THEME MUSIC]

 

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