DEAR DR. BLONZ: How old would a person have to be to be considered an “adult” when it comes to vitamins and supplements? My daughter is 14, and she has terrible eating habits, with her own set of quirks and refusals. I would really like her to take a supplement. I don’t know if she would be considered a child, and to take children’s vitamins, or an adult. She is active and not overweight. -- S.T., Broken Arrow, Oklahoma

DEAR S.T.: There isn’t any specific age at which a child magically becomes an adult. During the adolescent years, ages 13 through 17, the child transitions into their adult body, but this can vary from individual to individual. Some medications direct you to use adult dosing from age 12 on, while other medications might have separate guidelines up to age 18. That is why it is important to always follow the directions for each product. After all, a child is not a miniature adult; pharmaceutical dosages are based on the way a drug acts in each given age group.

As far as vitamins and minerals are concerned, the “daily values” on the labels are set for adults and children over the age of 4, which would indicate that your daughter is most definitely in adult status.

Do your best to educate her regarding the importance of good food and good nutrition, especially as regards the need for calcium and other essential minerals. Teens and young adults need to appreciate that the first 35 years of life is the critical period during which their bones can put on more mass than they lose, but this only happens when there is an adequate intake of calcium. The fourth decade of life is when we begin to shift gears, and any bone mass present serves as a “savings account” for the slow but incessant drain that occurs in the decades ahead. An active lifestyle is also important, but healthful dietary habits during the first half of life are critical. If your daughter is not going to be getting all she needs in her diet, a supplement can serve as a reasonable alternative, but it’s not a long-term solution.

Childhood and adolescent food quirks and refusals may come across as a challenge to your authority, but mealtime should not be allowed to degenerate into a power struggle. Missing an occasional meal, failing to eat from all the food groups on a daily basis, or never touching the spinach or broccoli are not signs of impending malnutrition. The body has amazing powers to conserve needed nutrients and make the most of them when they finally appear.

There’s no way to predict how individual tastes develop; they are facts of a child’s life that tend to ebb and flow over time. Talk with other parents. What a child’s peers enjoy can hold sway over their preferences.

In the end, aim to instill a sense of appreciation for all that’s involved in bringing food to the table in a supportive family setting. Add a nudge toward a healthy food selection, be consistent with the example you set, and you’re on track for promoting long-term healthful habits.

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: At times during the previous year, I took St. John’s wort for periodic bouts of mild depression. I have had little success with the prescription antidepressants I have tried. Does the fact that I have not had any problems with my St. John’s wort indicate that I can continue taking it? -- S.C., Tulsa, Oklahoma

DEAR S.C.: We all need to appreciate that the human body has sophisticated systems designed to protect it from potential dangers posed by unfamiliar substances. These systems try to detoxify, break down or eliminate “foreign” compounds that enter the body. Foreign compounds can include everything from herbal products and prescription or over-the-counter (OTC) drugs to pesticides and environmental pollutants. It doesn’t matter that some of these might be thought of as beneficial; foreign compounds get identified as such, and processed for elimination.

The complexity starts because there can be multiple compounds processed at any given time. This gives rise to interactions between medications and herbs that can affect the way they work and the rate they get eliminated from the body. Our liver is the focus of this process. The method typically involves a reaction with the substance that’s tantamount to putting metabolic handcuffs on it, preventing it from being active while it’s in queue for elimination.

A specific family of enzymes plays a key role in metabolizing, or breaking down, unknown substances. Compounds broken down via this enzymatic system include herbs; drugs used to treat heart disease, HIV infections, seizures, depression and cancer; drugs used to prevent the rejection of transplanted organs; and oral contraceptives. Different substances can either compete with each other for enzyme attention -- resulting in slower decreases in their respective blood levels -- or they can stimulate the enzymes, which results in a more rapid decline. This is significant for health conditions where reliable medication blood levels are a key part of the treatment.

St. John’s wort is metabolized by this enzyme system, and it acts as a stimulant. That means that if St. John’s wort is being taken, the blood levels of other drugs can be lower than expected -- lower, even, than needed to achieve that drug’s therapeutic effect.

I don’t know if you are taking other medications or substances, but this is definitely a discussion you should have with your physician or pharmacist without delay.

Before prescription drugs are approved by the Food and Drug Administration, they have to undergo rigorous testing for safety and efficacy. Tests are also done to determine how a drug works, the effective dose, any potential side effects or adverse reactions, how long the drug lasts, and how it is eventually eliminated from the body. All this helps to provide the information used by health professionals when dispensing the drugs. For OTC drugs, this info is available for you either on the package or in the package insert.

Herbs have been in use for centuries, and some may have health-boosting potential. Our knowledge, however, about side effects and interactions with other medications -- even with other herbs -- is still in its infancy. That is one of the reasons why people should approach the use of herbs with caution, especially when also using other medications. There are websites providing interaction information, including drugs.com and rxlist.com, but these should not be considered a substitute for that talk with your health professional.

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 have been a vegetarian for about 10 years. Lately I have been having problems with muscle discomfort in my shoulder, and some people have been telling me that it might not be healing correctly because I do not eat red meat. I don’t buy this at all, but was wondering: Is there anything I should supplement my diet with, since I no longer eat red meat? -- K., San Diego

DEAR K.: A plant-based, whole-foods diet is the way to go, and good nutrition is good nutrition, whether or not there’s ever meat on the plate. You did not mention whether you consume other animal products, but if you eat vegetarian, there are some nutrients you should be mindful of. These include vitamin B12, calcium, iron, zinc and vitamin D.

In most cases, getting adequate protein doesn’t represent any problem for vegetarians. Amino acids are the building blocks of protein, and of the 22 different amino acids, our body can manufacture all but nine. These nine, referred to as the essential amino acids (EAAs), need to be supplied by our diet. Most foods contain some amino acids. Animal proteins, such as meat, poultry, fish, eggs and dairy are considered “complete” proteins because they contain all the EAAs.

Except for soybeans, vegetable proteins such as grains and legumes are incomplete proteins because they lack one or more of the EAAs. Vegetarians easily meet their daily protein requirement by combining different foods so that sufficient amounts of all the EAAs are consumed over the course of the day.

Vitamin B12 is needed for red blood cells and nerve tissue, and it is only found in bacteria and animal foods. Vegetarians can use specially fermented soy products, such as tempeh or miso, as a dietary source for B12, or rely on foods fortified with it.

If you consume dairy products, there shouldn’t be a problem getting enough calcium. If not, you will have to rely on calcium-rich foods such as broccoli, dark green leafy vegetables (such as kale and turnip greens), calcium-set tofu, almonds, figs and some legumes. There is also the growing variety of calcium-fortified non-dairy milks, and fortified orange juice.

Red meat is an excellent source of iron, but it is also found in dark green leafy vegetables, legumes, raisins and prunes. Iron absorption is facilitated by acidic foods, such as citrus juices. Zinc, which can also be in short supply for vegetarians, can be found in nuts, seeds, whole grains and legumes.

Vitamin D, needed for calcium absorption and bone formation, is another nutrient that’s not widely available in vegetarian cuisine. Besides food sources such as fish and fortified milk products, the body produces this nutrient upon exposure to direct sunlight. An alternative is to rely on a supplement.

Back to your question about that muscle problem that is not healing: Your physician or health professional may have done routine blood work, and this can help verify if there are indications of a nutritional deficiency. You might also consider getting a referral to a physical therapist, who might help with specific strategies and exercises to help strengthen the affected muscle and get that discomfort into the history books.

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.