Q: The other day in a health-food store, I picked up an article that said we ought to have 300 micrograms of selenium a day. I recalled reading in your column that selenium can be toxic at levels not very far above what we need. Do you consider this to be too much?

A: Yes. The estimated "safe and adequate" range of intake for selenium is set at between 50 and 200 micrograms (mcg.) a day. It is true that the selenium content of foods depends on where they were raised. But because we eat a varied diet containing foods produced in many different parts of the country, our food should provide all the selenium we require. There is no evidence that additional amounts can ward off cancer or retard the aging process.

Then there is the matter of toxic symptoms. Research has not yet unveiled a clear-cut picture of the level at which such symptoms appear, but according to the 1980 edition of the Recommended Dietary Allowances, "The demonstrated chronic toxicity of relatively low dietary levels in experimental animals suggests a maximal intake of 200 mcg. a day for adults, which should not be exceeded habitually if the risk of long-term chronic exposure is to be avoided."

All these reasons lead us to question the wisdom of taking a supplement that is 50 percent above the estimated limit of safe and adequate intake.

Q: While shopping in an Italian market, I noticed a vegetable that was new to me. It looked like a giant bunch of pale celery with coarse stalks. I was told its name was cardoon. Can you tell me more? How should it be prepared?

A: Cardoon, like the globe artichoke, is a member of the thistle family and native to the Mediterranean. The tough outer stems and leaves must be stripped away to get to the inner stalks and firm hearts. To be eaten raw, the strings and inner white skin are trimmed and the stalks cut into serving pieces. The heart is usually sliced thin and held until serving time in water with a little vinegar or lemon juice added to prevent darkening. One of the more popular sauces that commonly accompany it is heavily seasoned with garlic and anchovies.

Alternatively, the vegetable may be prepared in a number of other ways that take more time and effort. First, the stalks are blanched for 15 minutes or so in acidulated water, then drained and rinsed. This allows the skins and strings to be peeled away more easily. Cooking may then be finished by simmering the stalks until they are tender (20 minutes or longer) in water or, for extra flavor, in beef broth. The cooked vegetable might then be served with a vinaigrette, but it could also be combined with onions and other vegetables, served with cheese sauce, or prepared as you would braised celery.

Over 90 percent water by weight, cardoons are low in calories, only 20 in 3 1/2 ounces of the cooked vegetable. Beyond that, it is nutritionally unremarkable. However, it is one of the vegetables that contain larger amounts of sodium than most, a concern only to those who must sharply restrict sodium intake.

The purple flower of the cardoon is occasionally used as an alternative to rennet in the making of cheese in one region of France. The flowers contain a substance that clots the curds, allowing them to separate from the whey.

Q: Could you please explain the difference between ice cream labeled "vanilla flavored" and that which is labeled only "vanilla"?

A: The difference relates to whether the flavor is all natural or part artificial. "Vanilla" ice cream contains only pure vanilla, while "vanilla flavored" makes use of both natural and artificial flavor. But the federal Standards of Identity dictate that in order to employ the term "vanilla flavored," the natural flavor must predominate.

Specifications for the third type of labeling might come as somewhat of a surprise. Ice cream labeled as "artificially flavored" may contain either all artificial flavor or a combination of natural and artificial flavors. In this case, however, the artificial ingredient would be the one to predominate.

Regulations that govern ice-cream labeling are quite detailed. They specify the size of letters to be used and the placement of the words describing the flavoring ingredients. They also clearly define exactly how the predominant flavor is to be measured.