DEAR DR. BLONZ: I have no thyroid problems, but during a recent lecture on iodine, the presenter described a simple test to determine if you are deficient. It involved buying some iodine antiseptic and painting it inside your forearm or thigh. If you wake up the following day and the iodine is still visible, it indicates your body has sufficient iodine. But if the dark color has faded, it indicates your body is iodine-deficient. I wanted your thoughts. -- H.T., Scottsdale, Arizona

DEAR H.T.: Iodine is an essential trace element needed for thyroid hormones, which are substances that help regulate the metabolism. The daily value for adults is 150 mcg, but it is higher during pregnancy and breastfeeding (more on iodine from the NIH at b.link/chse3n).

Absorbed iodine travels in the blood and gets removed by the thyroid, a butterfly-shaped gland at the front of the neck below the larynx. If the body were chronically iodine-deficient, the thyroid gland would enlarge to do a more efficient job of grabbing iodine from the blood. At this point, a condition known as goiter would have developed, including a noticeable bulge in the lower throat area. Iodine is plentiful in the ocean, but is not well-distributed on land. In the U.S., areas where iodine deficiency was common in the early 1900s -- including the Great Lakes, the Appalachian Mountains and the inland Northwest -- came to be known as the "goiter belt." In the 1920s, as a public health measure, the government encouraged manufacturers to add iodine to table salt -- a move that drastically reduced the incidence of goiter.

On a side note, iodine has a connection to nuclear accidents, which often involve a release of radioactive iodine (radioiodine) into the environment. Radioiodine can be absorbed by the body and destroy cells in the thyroid and elsewhere. An iodine deficiency makes one particularly vulnerable to such damage. While those in an area with a radiation emergency are advised to evacuate, another protection can be to take a potassium iodide supplement, which would satisfy the body's need for iodine and protect the thyroid from that danger.

Today, it's uncommon for anyone eating a varied diet to suffer from an iodine deficiency, especially when iodized salt is used. Food containing iodine is limited to seafoods, crops grown in coastal areas and dairy or meat from animals that graze on feed that's supplemented with iodine.

Now, back to your question. There are established, reliable ways to determine whether your body is iodine-deficient, and the method you describe would not be on that list. The procedure you describe, sometimes called an "iodine patch test," is unreliable. Iodine applied to the skin can be absorbed, and it can happen more rapidly if there is a severe deficiency, but the iodine will also lose its color when it converts to (colorless) iodide, a process that can occur irrespective of the level of iodine in the body. That patch test may work under some circumstances, but it is not considered a reliable indicator of your iodine status.

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 keep reading about "buying locally." I can see the good in that it would involve fewer resources, but it seems that if you buy all your food from your area, you wind up with the nutrients only from that area, and might miss others. I am curious about the possible benefits of getting food that is grown all over the world. -- B.K.

DEAR B.K.: "Seasonality," where we are limited to foods available during periods in which they are harvested, is less of an issue in today's fully stocked supermarkets. Much depends on where you live; there is less impact in a state like California, where vast agricultural resources and temperature-controlled transportation methods keep fresh produce available throughout the year. But even with bountiful harvests, there will be periods during which specific foods may not be available. (One of my favorites is dry-farmed Early Girl tomatoes, which are around only a few months of the year. To my palate, no other tomatoes come close.)

Store shelves remain full as grocers purchase fresh foods grown worldwide and organically grown produce available from the Southern Hemisphere when it's winter in the north. We should support local agriculture by buying locally and patronizing farmers markets when possible. Quality can vary, as some regions do a better job with specific foods than others; this is often based on cultural traditions perfected over generations. As for potential health benefits, nutrients reflect more the quality and variety of what you eat rather than where it was grown.

DEAR DR. BLONZ: After I get my dietetics degree, I am considering graduate school, with the goal of working for a food company to develop nutritious foods with less processing, ideally by using controlled atmospheres. I want to develop, test and promote various food products, create new recipes and improve existing ones. Would getting a graduate degree in food science or nutrition be more beneficial? I would appreciate your opinion since this is your area of specialty. -- J.D.

DEAR J.D.: A dietetics degree will provide a foundational understanding of how nutrients work in the body. A graduate food science degree would seem logical if you want to work in the food industry. In addition to learning essential information about food production science, you would be more marketable when looking for a job. Consider a school with food science and nutrition departments; some may have these combined. The Institute of Food Technologists may be a good resource. This professional organization is based in Chicago, and it provides information about careers in the food industry (ift.org).

As you compile a list of possible schools, check online for a list of faculty research interests. Academic departments' successes depend on their faculty's strengths, and reviewing their interests is an excellent way to see how a department is oriented. In graduate school, you will take the required coursework, but will be associated with a professor to guide you on projects. You'll be ahead of the game if you find a school with one or more faculty members that either speak to your current interests, or describe an area of research you want to pursue.

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: A recent magazine article suggested that daily vitamins aren't necessary for adults over 65. Do you agree? -- T.G.

DEAR T.G.: I don't see it that way, but let me share the backstory. I do not favor using daily vitamins as an excuse for not making efforts toward a healthful diet and lifestyle. And it is incorrect to think that getting all of the "essentials" in a pill will cover all the nutritional bases. Vitamins can supplement healthful eating, especially when you need certain essential nutrients not typically present at recommended levels in your foods.

History is instructive here. Essential nutrients were discovered when things went wrong in experiments where all known essentials were thought to have been provided. Subsequent reviews discovered that one or more missing substances were responsible for the results, which were then studied and eventually added to the list of essentials. The different vitamin letters and numbers show that this has been an ongoing process -- and we are not done yet. (Check b.link/67v67w for a story of vitamin history.)

Next, consider that most discoveries were made when short-term studies found unexpected outcomes. We seem to have done well with substances where deficiencies give rise to immediate effects, but what about those needed to impact long-term outcomes for aging and chronic disease? My advice is to look to nature, where the successful evolution of plants serves as an object lesson. With plant-based, whole-food eating, we get "known" essentials packed with partner substances to complement their action. (My prediction is that those partner substances will be where future essentials will be discovered.)

Nutrients work with teams of substances in complex biochemical reactions. Similar to how exceptional talent is valued in an orchestra, sports team or business, the entire ensemble is needed to succeed -- the system is only as strong as its weakest link.

Whole foods evolved by making teams of interacting protective substances to protect the plant and facilitate its ability to produce its next generation. When such foods are at the core of our eating plan, we import these benefits into our bodies. Evidence can't say the same thing regarding poor eating habits. For example, vitamin C -- ascorbic acid -- is a powerful antioxidant and free-radical scavenger. It works well when part of a whole food, such as citrus, where it comes with other nutrients, dietary fiber and a support staff of "co-worker" antioxidants to help. If you add a bunch of vitamin C to junk-food eating, it will still do its dance. But without any support staff, the vitamin C -- particularly if taken in excessive amounts -- can become a pro-oxidant and cause the very damage that it was taken to prevent.

Back to your straightforward question: Plant-based whole-food eating must be primary; a multivitamin can supplement such a diet. If healthful eating is on the scene, I have no problems with their use.

Read more about vitamins at b.link/zhf8g6. You can also check out Consumerlab.com, a subscription site that tests and reviews various multivitamins and supplements.

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.