WASHINGTON — Tales of Vitamin A toxicity are often bizarre, centering on Arctic explorers eating huge amounts of polar bear liver or fitness fanatics gobbling handfuls of vitamin supplements.

But Americans should be aware that more subtle overloads of Vitamin A might pose some serious health risks, particularly to pregnant women, children and the elderly, federal nutrition experts say.

The ideal Vitamin A intake for the average man is about 3,100 to 3,300 international units (IU) daily, according to the National Research Council's 1989 edition of the Recommended Dietary Allowances (RDAs).

But Dr. John Hathcock of the Food and Drug Administration estimates 3% to 4% of the U.S. population takes vitamin supplements containing 25,000 IU or more of Vitamin A per day.

"That's a heck of a lot of people. If even 0.1% of the population are taking potentially toxic doses, that's too high," Hathcock said, adding that the FDA is still trying to determine at what level the vitamin meets the government's "generally recognized as safe" standard.

So far, Vitamin A toxicity--which may induce bone abnormalities and life-threatening liver damage--has been conclusively shown only in adults who consistently consume more than 50,000 IU daily of Vitamin A and young children who take more than 20,000 IU daily.

But Hathcock said a growing body of research indicates the Vitamin A safety threshold may be far lower for certain high-risk groups.

"The question is not the upper limits, but rather how little can possibly cause problems," the nutrition expert told a recent seminar.

Vitamin A is a group of compounds essential to vision, cell growth and immune function.

In nutritional supplements, Vitamin A generally refers to retinol, also known as "preformed Vitamin A." Food sources of preformed Vitamin A are primarily limited to liver and fish liver oils, and it is rare for toxicity to stem from diet alone, Hathcock said.

The body can also convert precursors called carotenoids into Vitamin A. Carotenoids, which are found in carrots, spinach and many other vegetables, are absorbed through the intestine far less efficiently than retinoids. But they are not known to be toxic even when taken in large doses over long periods of time.

Much of the worry over Vitamin A's safety arose in the mid-1980s after it became evident that the anti-acne drug Accutane, which is a powerful analog of retinol, caused birth defects if taken during the early weeks of pregnancy.