Are crabs and oysters good for your eyes?

Johns Hopkins researchers have a report in the the journal Opthalmology that sends a mixed  message about whether omega-3 fats protect the eyes.

And if you like to eat crab and oysters, enjoy—and we’re with you. But don’t expect any special ophthmalic benefits.

Fish and shellfish are natural sources of the omega-3 fats that are believed to pay all kinds of health dividends, and there are some good epidemiologic clues that eating fish reduces the likelihood of getting macular degeneration (no guarantee, but you improve the odds).

The Johns Hopkins study included 2,560 older residents (ages 65 to 84) residents of Salisbury, Maryland, a small city in the Eastern Shore region of the state. The residents answered questions about their eating habits and had their eye examined.

When the researchers sifted through the data looking for correlations, they found no suggestion of a protective connection between high fish and shellfish consumption and the precursors of macular degeneration, a common source of vision loss and blindness  among older Americans.

They did, though, see a correlation between high consumption and advanced states of macular degeneration. So you can tally this study in the plus column for omega-3s, perhaps with an asterisk.

Maryland is famous for its blue crabs. Of course, there are crab cakes, but people on the East Shore cook crabs whole, break open the shell with hammers, and eat the meat with a lot of spice.

And Chesapeake Bay is famous as a source of oysters, although pollution and overharvesting have threatened the population.

Nutritionally speaking, crab and oysters are distinctive for containing a great deal of zinc.

Zinc is thought to be good for the eyes, and it’s one of the ingredients in the AREDS vitamins that people take to slow the progression of macular degeneration.

So, putting two and two together, it was thought perhaps that the eyes of these older Eastern Shore residents might show evidence of a local diet rich in crab and oyster and therefore in zinc.

Alas, the data showed no such evidence. Yes, crab (4 milligrams per 100 grams) and oysters (182 milligrams per 100 grams) contain a lot of zinc. But you’d have to eat a whole lot of crab and oyster to match the 80 milligrams included in the standard AREDS vitamins.