DEAR DR. BLONZ: I am concerned about the mineral zinc and whether it is possible to get too much. The multivitamin and mineral supplement I use each contain 100% of the daily zinc requirement. I want to know if this could be a problem. -- F.F., Scottsdale, Arizona

DEAR F.F.: Zinc, like many essential nutrients, is involved in an impressive variety of bodily functions. Not only is zinc integral to a key enzyme in our immune system (glutathione peroxidase), but it also plays a role in our skin, hair, our sense of taste, proper calcification of the bones, and the development and operation of the sexual organs. Additionally, zinc is in several enzyme systems related to digestion, and, finally, zinc plays a role in the normal functioning of insulin -- the hormone that regulates the blood's sugar level.

An informative study in the Journal of the American Medical Association looked at 589 pregnant women with low zinc levels in their blood. Half the women in the study received 25 mg of a zinc supplement daily during pregnancy. The study found that supplementation improved their pregnancy outcomes by significantly increasing birth weight.

It is possible to get too much zinc, but the chance for toxicity is remote if your only source is the zinc in your diet. When taking it as a supplement, it's prudent not to take more than 40 mg a day unless specifically requested by your health professional. (For more on zinc's benefits, see b.link/eexcawg.)

DEAR DR. BLONZ: Often, when having sugarless gum or mints, I end up with cramps, or "the runs." My friend says I could be allergic to the artificial sweetener sorbitol. I doubt this because sometimes I can enjoy sugarless mints with no side effects. I want to be able to continue enjoying them. -- L.H., Richmond, California

DEAR L.H.: Sorbitol is not an artificial sweetener, because it occurs naturally in many fruits. However, while an allergy could be the issue, sorbitol would be a prime suspect for your G.I. discomforts. Sorbitol is a "sugarless sweetener" because it has a sweet taste -- about half as sweet as table sugar -- but doesn't promote tooth decay, and it's not absorbed from the digestive tract like other sugars.

The downside to sorbitol is that it attracts and holds water in the digestive tract, which can lead to diarrhea in some people. In addition, many bacterial flora in the large intestines can digest sorbitol, which release gas as their waste product, with obvious results. Small amounts of sorbitol may pass through without discernible symptoms. In larger quantities, as with several mints or sticks of sugarless gum -- particularly on an empty stomach -- the upset you described can result.

Anyone with problems using sorbitol or a similar synthetic sweetener, xylitol, should limit their intake or consume it only after a meal to slow its passage through the digestive system. (For more on sorbitol, see b.link/bcc7y84.)

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Why is it best to get vitamins from food rather than from supplements? Does the human body make the distinction, and if so, to what extent? -- R.S., Boston

DEAR R.S.: A vitamin is the same whether it comes from food or from a synthetic formula. To the human body, it's a chemical that fills a need. My response would be different if you had asked whether getting nutrients from whole foods is better.

We now has effective methods to diagnose nutrition deficiencies, and much of this data comes from population studies. However, science has only begun to investigate how certain health or genetic issues might affect what is best for a particular individual. Interactions with medications, and even between nutrients and herbs, must be considered. (For more on drug interactions with supplements and herbs, see b.link/ejz74zb.)

Modern science has come a long way, but we are far from knowing all there is to know. The human body may not be able to distinguish between a particular nutrient from food versus the identical substance provided as a supplement, but nature's whole foods typically contain complementary substances that help the nutrient do its job most effectively. Thus, it is always best to get the entire team, which comes from a nutrient in its whole-food context.

DEAR DR. BLONZ: I work to have a whole-food diet, as you recommend. Still, when I recently purchased vitamin and mineral supplements, I noticed that my mineral supplement contains calcium amino acid chelate, and my vitamin supplement contains D-calcium pantothenate. Why is this calcium compound in my vitamin? I have read that too much calcium can be toxic, so I want to ensure that I'm not taking too much calcium if both products provide similar ingredients. -- S.T., Dover, Delaware

DEAR S.T.: In the same way that its chemical name, ascorbic acid, also refers to vitamin C, the compound known as vitamin B5 can go by its chemical name, pantothenic acid.

The calcium in D-calcium pantothenate is indeed an essential mineral, but it would be best to think of it as a "salt" of pantothenic acid made from two molecules of the pantothenic acid joined with one calcium molecule. When dissolved, the calcium and the pantothenic acid go their separate ways, leaving the B5 to be available as the vitamin. The amount of calcium is negligible.

To illustrate: Say you took the adult daily value of pantothenic acid (5 milligrams) as D-calcium pantothenate. This would add less than one-half of one milligram of calcium to your daily total for this mineral, which has an adult daily value of 1,000 mg. Anything, including calcium, can become toxic if taken in excess. However, there is no issue here.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I know you're not a medical doctor, but I was hoping for some general guidance about the care my mother, who was diagnosed with thyroid cancer, is receiving. We are in a managed-care plan through my father's job, and I was hoping you might have some idea of how we could go about getting a second opinion to confirm her diagnosis and treatment plan. My friends have been telling me many different things, but my parents seem content with whatever the doctor says. Advice? -- F.E., New York

DEAR F.E.: I deeply sympathize with your situation. Getting a second opinion regarding diagnosis and treatment can be an important part of the approach to any complex medical situation.

Cancer is not a singular entity with consistent features. As such, the diagnosis of cancer can depend on interpretation of medical evidence, and indicators of any cancer's unique characteristics are not always clear-cut. Doctors can differ in their approaches; some are conservative, while others are more aggressive. And medical facilities can differ in their familiarity with and use of evolving technologies.

You should work with your parents to voice your concerns and verify that your mother's diagnosis and treatment strategy make medical sense. If you feel it is appropriate, raise the issue of getting a second opinion. Most physicians will respect the request for a different set of eyes to review a case, and insurance may cover it. If possible, find a cancer center or a university-affiliated teaching hospital, ideally with faculty who have researched the type of thyroid cancer affecting your mother. The National Institutes of Health provides information on finding cancer centers and doctors at b.link/y55yveu. In addition, check the American Cancer Society's Cancer Survivors Network at b.link/yxhhe8q for discussions from other patients who have been down this road. My best to you and your family during this difficult period.

DEAR DR. BLONZ: I learned in school that riboflavin in milk is destroyed by light. If that is true, why is milk sold in clear containers? Am I wasting my money by paying more for milk in opaque containers? -- S.T., Tulsa, Oklahoma

DEAR S.T.: Milk is a perishable food, and exposure to natural or bright fluorescent light can destroy a percentage of riboflavin (vitamin B2), vitamin C and vitamin B6 and, over time, encourage the development of "off" flavors. Light intensity, duration of exposure and time away from refrigeration will determine how much these nutrients are affected.

A healthful diet should include nutrients from many sources, so minor losses from one food should not negate the nutritional value of that food. That said, storage in an opaque container, such as a paper carton, seems to be best in preserving milk's nutrients, while clear glass -- while aesthetically pleasing, and recyclable -- is not. Always check the product's date to be sure you are enjoying fresh milk. (Read more on food product dating at b.link/cbsr87.)

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.