多吃萝卜 可以护眼呢

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Hope for Eye Disease Could Lie in Vegetables and Fruits

By Patti Truant

As the baby-boomer generation ages, some will join the 15 million Americans afflicted with age-related macular degeneration (AMD), the leading cause of blindness and vision loss in adults age 60 or older.

While some people with AMD have benefited from laser surgery, there is really no successful treatment or cure for the disease. But the work of a University of Maryland researcher shows that carotenoids, organic pigments necessary to plant growth, may hold a key to the prevention and treatment of the debilitating disorder.

Frederick Khachik, an adjunct professor in the chemistry department and senior research scientist for the Joint Institute for Food Safety and Applied Nutrition (JIFSAN) at Maryland, is looking at how the carotenoids lutein and zeaxanthin work in the human eye. They are the only carotenoids found in the retina, the area of the eye most exposed to harmful ultraviolet light. These carotenoids have two important beneficial qualities for the eye: they work as an optical filter to screen out UV rays, and act as antioxidants to prevent damage to eye cells.

"The scientific evidence strongly suggests that lutein and zeaxanthin play an important role in the prevention of age-related macular degeneration," Khachik said. "However, only future clinical studies with a large number of patients at various stages of AMD can unequivocally demonstrate such a protective effect. If this happens to be the case, I would be delighted that I could make a small contribution to such a significant accomplishment."

In fact, Khachik has already made concrete contributions, including a patented process for isolation and purification of lutein from extracts of marigolds, that is suitable for human use as a dietary supplement.

"Lutein had been known for nearly half a century," Khachik said, "but no attempt had been made to isolate large quantities of this carotenoid to study its biological properties that could lead to clinical investigations."

Promising Results

Lutein and zeaxanthin are found in foods such as green vegetables, corn, squash and citrus fruits. Khachik said that a nutritious diet should provide adequate amounts of carotenoids for most Americans.

"Obviously, if one consumes a diet that is rich in fruits and vegetables, there should be no need for supplementation with these carotenoids, but I am not sure if this is the case nationwide," he said.

Khachik's research is adding more pieces of the carotenoid puzzle, as the roles of lutein and zeaxanthin become gradually clearer. However, Khachik says, it is difficult to study the effects of the carotenoids in the human eye in a consistent, non-invasive way.

He has used monkeys and quails in previous studies, to see if high levels of the carotenoids produce toxicity. He found no toxicities, even with many of the doses grossly exceeding that which would be given to humans.

Khachik is planning several extensive studies in conjunction with the National Eye Institute (NEI). "We're hoping to get support from the NEI to conduct a three-year metabolic study with lutein."

Other projects in the works involve the role of lycopene in preventing prostate cancer and the effectiveness of carotenoids in preventing glaucoma.

Future Research

Khachik said he hopes to create more dietary supplements that include important carotenoids. He already has three patents on the conversion of lutein to alpha and beta cryptoxanthin, which has shown to be effective against bone disease and osteoperosis.

With a career dedicated to studying the role of nutrients on human health, Newsdesk couldn't help but wonder: What's in Dr. Khachik's own diet? Lots of fruits and vegetables, and of course the lutein supplement he helped develop, he said. But, he admitted, junk foods do slip in there once in a while.

"Diet plays a very major role in cancer prevention," he said, "but there are also definitely genetic factors."

For researchers such as Khachik, progress is often slow because the scientific process is by definition time-consuming and meticulous. But, Khachik said, all his efforts pay off when a new discovery offers the opportunity to increase understanding and potentially improve human health.

"The best part of my job is when I work on a project for months or years, and all of a sudden I have an answer to an outstanding problem and when I see the results of my work being used by others," he said.