DEAR DR. BLONZ: How dangerous are the nitrates that are in hot dogs, ham, sausages and deli meats? How do they differ from those found in vegetables? Are they all carcinogens that have to be actively avoided to reduce the risk of cancer? -- F.G., Berkeley, Calif.

DEAR F.G.: Your question involves both nitrates and nitrites; the two are related, but there are important differences.

Nitrites: Food processors use nitrites as preservatives in cured and smoked meat products such as bacon, sausage, smoked and deli meats. These are all meats that tend to be stored under refrigeration for a number of days, and without an appropriate preservative such as sodium nitrite, there's a relatively high risk of botulism -- an often-fatal food poisoning. Nitrites, themselves, represent a risk as they can form cancer-causing chemicals called nitrosamines. These compounds can form when a nitrite (either sodium nitrite or potassium nitrite) reacts with protein at a high cooking temperature. The principle here is that with the exception of freezing or high-temperature cooking, there's no safe way to protect against botulism in a low-acid food such as a cured meat.

Nitrates: Nitrates occur naturally in several vegetables including turnip greens, beets, celery, rhubarb, spinach, radish, parsley and lettuce. They represent less of a risk than nitrites, but a nitrate can be converted to a nitrite in the stomach. This means that nitrosamines can theoretically form in the stomach when you eat a nitrate-containing vegetable and a protein food at the same meal. The important difference is that antioxidant nutrients can help limit nitrosamine formation, and these nutrients, such as vitamin C, E or antioxidant phytochemicals, tend to be found in nitrate-containing foods.

By contrast, in cured meat products such as bacon or sausage, all the ingredients needed to form nitrosamines are in the same package and the nitrosamines can be formed before you eat. In weighing the relative risk from botulism against the presence of the nitrite preservative, scientists decided that if you're going to eat cured or smoked meats, the use of nitrate preservatives is an acceptable risk.

Because there is some risk involved, nitrite preservatives are not permitted in baby foods.

Although most smoked and cured meats contain sodium or potassium nitrite, you can find nitrite-free meat products either as locally made, short shelf-life products, or in the freezer case where the low temperature can effectively inhibit bacterial growth.

A prudent approach is to limit your intake of nitrite-containing cured and smoked meats. If you enjoy these foods, see if a nitrite-free brand is available. You could also look for a product that contains sodium ascorbate (a salt of vitamin C), sodium erythorbate or vitamin E; these antioxidants can help limit nitrosamine formation. Another option is to make sure you have antioxidant-rich foods at the same meal as the nitrite-containing meats. A salad with the meal, some peppers or vegetables on the sandwich, and fruits as dessert are all additions that could help blunt the potential risk.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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 am in high school, and want to put on weight so I can play football. I recently shot up a number of inches in height, but my weight proportion has not kept up. I have always been in the backfield, and now I lift weights four mornings a week and take physical conditioning. I have been eating and eating but it does not seem to help me bulk up the way I would like. Could you recommend a supplement? -- F.F., Chicago

DEAR F.F.: There is a limit to what one can do, as growth in height does not always parallel the increase in weight. Then there is the overriding influence of one's genetic predisposition. If most of your family members are tall and thin, it will lessen the odds of you becoming a 250-pound running back. This is not to say you are without any remedies, but they might not provide the exact results you hope for.

A well-balanced diet, along with weight-lifting and conditioning programs, are important adjuncts to any weight-gain program. If you wanted to gain one pound a week, this would involve taking in 500 calories a day above your normal caloric intake. There are weight-gain milkshake products that can help accomplish this, but be advised that studies have found that the body does not always gain as expected. You are not the first to face this dilemma. Remaining athletic might mean playing a different position, or even a different sport, that fits your new body type.

DEAR DR. BLONZ: I am a woman, and my hair is thin and subject to frequent breakage. Someone suggested Norwegian kelp. Will this nutrient remedy my symptoms and stimulate hair growth? -- T.T., San Diego

DEAR T.T.: Kelp, a vegetable that grows in the sea, is touted primarily for its iodine content, but it also contains potassium, calcium, magnesium and sodium. Iodine is an essential mineral that plays a role in the manufacture of the thyroid hormones that help regulate the body's metabolism. Dry, coarse, breaking hair and hair loss are among the symptoms of inadequate thyroid hormone (hypothyroidism), so perhaps that was the connection that your adviser was thinking of.

It is unclear whether kelp is the answer to your problem. Iodine is plentiful in the ocean but is not well-distributed on land. Foods containing iodine are limited to seafoods, crops grown in coastal areas, and dairy or meats from animals that have grazed on feed containing iodine. The Daily Value for iodine is 150 micrograms -- a trace amount. It's rare for anyone eating a varied diet today to suffer from an iodine deficiency.

One's genetic background, certain health conditions and medications can all have a range of influences on how the hair looks and behaves. The quality of your diet is also a player. I would take a look at what you have been eating and aim for a good mix of fruits, greens and grains as these provide the essential vitamins and minerals. I would also have a regular intake of seafood, or other sources of essential fatty acids. But irrespective of what one eats, the hair will always be greatly influenced by environmental factors and the hair products and treatments one uses. A knowledgeable hairstylist might be able to recommend products well-suited to your particular situation.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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 have always wanted to know if there was any connection between getting a cold and having a cold sore. What can be done with the diet to help prevent cold sores? -- J.B., Davis, Calif.

DEAR J.B.: Although it is referred to as a cold sore (or fever blister), the connection with an actual cold or fever is minimal. About the only thing they have in common is that a virus is responsible, but it's not even the same virus. The cold sore is brought on by the activities of a specific virus -- herpes simplex virus 1 (HSV-1) -- while the common cold is caused by a different family of viral organisms. Most of us get over a cold in about a week and the cold virus is history. A cold sore may disappear in the same amount of time, but HSV-1 tends to hang around, lying dormant in our nerve cells while it awaits the next opportunity to attack. It is quite a common infection; in fact, the National Institutes of Health report that most adults are infected with HSV-1 by age 20 (tinyurl.com/pxeqa).

A possible correlation between having a cold and developing an outbreak of cold sores could be the fact that our immune system gets taxed by an ongoing cold, and this would provide an opportunity for the herpes virus to come out and play. Other factors that can provoke a cold sore outbreak include stress, fever, an injury to the lips or mouth or excessive exposure to cold, sun or wind.

There are antiviral medications that can help fight an infection, so you can check with your physician if this is a recurrent problem. As for your diet question, there does appear to be a dietary connection. The HSV-1 virus may have an appetite for the amino acid arginine -- found in chocolate, grains, nuts and nut butters -- while having a distaste for the amino acid lysine, which is found in eggs, potatoes and dairy products. If you tend to suffer from cold sores, you might consider increasing the ratio of lysine to arginine in your diet, particularly if you feel an outbreak coming on. A more convenient approach would be to take a lysine supplement.

DEAR DR. BLONZ: Are there any nutrients that could contribute to the tendency to develop dark circles under the eyes? -- S.Q., Sonoma, Ariz.

DEAR S.Q.: Darkness under the eyes can be brought about by a number of factors. Perhaps the most common cause is a natural thinness in the skin under the eyes. The skin isn't dark, but at that location it is easier to see the vascular bed underneath. This trait can run in families and it doesn't necessarily reflect any health problem. If one is fatigued or under stress, the skin can become pale and this could accentuate the darkness. Then there is the fact that facial skin, and the subdermal fat layer, can thin a bit as we age. Unfortunately, aside from the general nutrients needed for normal health, there are no vitamins, minerals or herbal supplements that have demonstrated an ability to help eliminate this problem.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 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.