—Vitamins are substances that are "vital" to life. One source says, "Hundreds of foods deliver more than a dozen vitamins that participate in thousands of activities throughout our body." Wow.

Unlike fat, protein and carbohydrates, vitamins do not contain calories. Neither do they produce energy. They do, however, help to release energy from fat, protein and carbohydrates.

—Vitamins are needed in teeny-tiny amounts. Whereas we measure fat, protein and carbohydrates in grams (1 ounce equals 28 grams), vitamins are required in milligrams (one-thousandth of a gram) or micrograms (one-thousandths of a milligram).

— Water soluble vitamins such as vitamin C and the B-vitamins are destroyed by exposure to air. (As soon as you cut an orange, it begins to lose vitamin C.) So, eat fruit as close to fresh as possible. And refrigerate most fruit and vegetables in airtight containers.

—Microwave cooking is a good way to cook vegetables because it requires less heat and water exposure that can destroy some vitamins.

—One vitamin that is destroyed by microwave cooking, however, is vitamin B-12. So, best cook your meats and milk products (major sources of vitamin B-12) on the stove or in the oven ... not in the microwave, say food science experts.

—Vitamin A is one of those "more is not better" vitamins. Although vital for vision (vitamin A deficiency causes blindness) and maintaining the lining of all our body surfaces (skin on the outside and lining of our intestinal tract and other organs on the inside), excessive vitamin A can weaken bones and cause birth defects if too much is ingested during the early weeks of pregnancy. Best to get vitamin A (or its cousin, beta carotene, which converts to vitamin A in the body) in foods such as milk, cheese, eggs and brightly colored fruits and vegetables.

— Beta carotene —one of many "carotenoid" substances found in green orange, yellow and red-colored fruits and vegetables that act as powerful antioxidants and disease fighters — relies on the presence of fat to be effectively absorbed into the body. More beta carotene is absorbed when using a low-fat salad dressing, for example, than when using one that is fat-free.

—Vitamin D is an unusual vitamin because it is not essential that we get it in food or supplements. That's because vitamin D is primarily made when our skin is exposed to sunlight. (Most folks need to get it both ways, however.)

—If you draw a line across the United States and connect San Francisco, Salt Lake City, Denver, St. Louis, Indianapolis, Washington, D.C., and New York City, the line will be at approximately 40 degrees latitude.

Researchers say that folks who live above (or north) of this imaginary line can just about forget getting any vitamin D synthesis on their skin from the sun for four months every winter (November through February). Because vitamin D does not occur naturally in many foods, a supplement of this nutrient is often a very good idea.

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(Barbara Quinn is a registered dietitian and certified diabetes educator at the Community Hospital of the Monterey Peninsula. Email her at bquinn@chomp.org.)