They say you can never be too rich or too thin. But is it possible to eat too many leafy green vegetables?

Last year, an 88-year-old woman was admitted to NYU Langone Medical Center in a nearly comatose state, unable to walk or swallow and barely able to breathe. Though she had no history of thyroid disease, she was given a diagnosis of myxedema coma, a life-threatening condition caused by extreme hypothyroidism, or low thyroid function.

The culprit, it turned out, was raw bok choy. The patient had been eating two to three pounds of it every day for several months, in the belief it would help control her diabetes. Instead, the vegetables may have suppressed her thyroid, according to NYU physicians who described the case in a letter in the May 20 issue of The New England Journal of Medicine.

Bok choy contains compounds called glucosinolates that have been found to inhibit thyroid function in animals.