Macular Degeneration and Glycemic Index

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A new study has found that eating carbohydrate-rich food with a high

glycemic index — a measure of a food's potential to raise blood

glucose levels — is associated with the development of macular

degeneration.

The glycemic index is a measure of how fast carbohydrates are

metabolized — the faster they are broken down into glucose, the higher

the glycemic index. Simple carbohydrates, like those in cakes and

cookies, cheese pizza, white bread or other foods sweetened with sugar

or corn syrup, are quickly metabolized by the cells, while the complex

carbohydrates in brown rice, barley and many other vegetables are

broken down more slowly.

Heavy consumption of foods with a high glycemic index has been

implicated in the development of diabetes, cardiovascular disease and

some cancers, according to background information in the paper, which

appears in the July issue of The American Journal of Clinical Nutrition.

The researchers examined 4,099 people ages 55 to 80 enrolled in a

larger long-term study of eye health. Each participant had 20/32

vision in at least one eye, and the lens of the eye had to be clear

enough to allow good photographs that could be used to diagnose

macular degeneration.

None of the participants had diabetes. Using these criteria, the

scientists had 8,125 eyes to analyze. They graded the severity of

macular degeneration on a scale of one to five, administered food

frequency questionnaires and calculated the dietary glycemic index, a

number indicating the quantity of high-glycemic foods consumed, for

each participant.

After controlling for age, sex, education level, body mass index,

alcohol consumption and other variables, they found that the higher

the dietary glycemic index, the more likely a person was to have

macular degeneration. Those in the highest one-fifth of the dietary

glycemic index had more than a 40 percent increased risk of

significant macular degeneration than those in the lowest one-fifth.

The amount of carbohydrate consumed was not correlated with disease,

suggesting that it is only carbohydrates with a high glycemic index

that cause the effect.

" Sugar is fuel for the cells, but too much is destructive, " said

, the senior author of the paper and chief of the Laboratory for

Nutrition and Vision Research at Tufts University. " It is known from

laboratory and animal studies that carbohydrates can damage the

proteins in cells and affect their function. The sugars actually

modify things, modify the proteins, and it's the accumulation of this

modified stuff that is poisonous to cells. "

While the exact mechanism is unknown, the authors suggest that high

glucose concentrations are harmful to the retina and the capillaries

that supply the eyes, and that a diet of high glycemic index foods

causes oxidative stress that increases inflammation.

It may also be that the sharp temporary increase in blood lipid levels

that can follow consumption of simple carbohydrates plays a role in

damaging the blood vessels.

Still, the researchers say, older age, lower education level and

smoking are all more significant risk factors for age-related macular

degeneration than diet. They also say that the study does not prove a

cause-and-effect relationship between a high glycemic diet and macular

degeneration, that the study is based on observations made at a single

point in time, and that long-term prospective studies will be needed

before any firm conclusions can be drawn about the precise

relationship between diet and macular degeneration.

Dr. does not advocate a carbohydrate-free diet.

" I'm not an advocate of any extreme diet, " he said. " But self-control

and limiting exposure to simple sugars is not a bad idea. "

He added: " People are eating more simple sugar than they used to, and

reverting to a diet that is more fruits and vegetables and less

sweetened food would help. It doesn't take a lot of change. "

Link to abstract at American Journal of Clinical Nutrition:

http://www.ajcn.org/cgi/content/abstract/86/1/180