People have long known about the basic components of food—carbohydrates, fats, and proteins—but it wasn’t until the beginning of the twentieth century that sci-entists became aware that other compounds in food were necessary for the basic functions of life in animals and humans. The substances are often called
micronu-trients because, with the exception of some minerals like calcium, phosphorus, and sodium, most of them are present only in very small amounts in the body. But they pull much more than their weight in keeping our bodies running.
Most micronutrients were initially discovered for their role in certain vital func-tions of the body, often because a lack of a vitamin led to a specific disease. Vita-mins are often grouped into two classes: fat-soluble (vitaVita-mins A, D, E, and K) and water-soluble (vitamin C, thiamin [B1], riboflavin [B2], niacin [B3], choline, pan-tothenic acid [B5], vitamin B6, folate, vitamin B12, and biotin). The main differ-ence between the two is that fat-soluble vitamins can accumulate in the body, while water-soluble ones are usually excreted and must be replaced more regularly.
Because of their longer staying power, fat-soluble vitamins can become toxic in high doses.
Minerals are considered inorganic compounds because they contain no carbon, but are used in many capacities in the body, from building bones to keeping the immune system functioning. Lately, there has been a lot of research accumulating that certain trace elements—so called because together they make up less than 0.01 percent of our body weight—have functions in the body that make them an impor-tant part of our diet.
Here are a few of the vitamins and minerals that are frequently low in kids’ diets.
Also see Table 9.1 for a list of all vitamins, minerals, and trace elements that we know are important for health, and where to find them in foods.
Vitamin A
The first vitamin of the alphabet was also the first vitamin discovered, when scien-tists isolated the fat-soluble factor from foods that was given the name vitamin A in 1920. Later it was found that certain vegetable pigments, called carotenoids, are converted into vitamin A in the body. Vitamin A has a role in vision, enabling us to see in dim light. It also keeps the immune system strong, and for this reason is often given as supplements to children in developing countries who are at risk for infections. It also has a role in growth and helps promote the absorption of iron—
only one example of how adequate supplies of one nutrient can have an effect on another. Natural sources of vitamin A and carotenoids are liver, fish liver oils, eggs, dairy products, deep orange fruits and vegetables, and dark leafy vegetables.
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Table 9.1Micronutrients and Their Food Sources MICRONUTRIENTBIOLOGICAL FUNCTIONSFOOD SOURCES Fat-Soluble Vitamins Vitamin ANecessary for normal vision, develop-Preformed vitamin A can be found in liver, fish liver oils, fish, eggs, and dairy ment, and immune functionproducts. You’ll find carotenoids (provitamin A) in dark leafy green vegetables and deep orange fruits and vegetables. Vitamin DHelps build bones by regulating calcium Sunlight (through the skin), some fatty fish and fish liver oils, fortified cereals, and phosphorusfortified milk or margarine, and vitamin D supplements Vitamin EAntioxidant defenseVegetable oils, wheat germ, nuts, green leafy vegetables, and whole grains Vitamin KComponent of many blood proteins; Green leafy vegetables, brussels sprouts, cabbage, milk, eggs, and margarine needed for blood clotting Water-Soluble Vitamins Thiamin Used to metabolize carbohydrates Whole and fortified grains and cereals, pork, nuts, seeds, tuna, salmon, (vitamin B1)and some proteinsbeans, tofu, and vegetables including peas, asparagus, and okra Riboflavin Component of several chemical Fortified grains and cereals, dairy products, eggs, meat, almonds, tofu, (vitamin B2)reactions in cells; regulates some beet greens, and spinach hormones
MICRONUTRIENTBIOLOGICAL FUNCTIONSFOOD SOURCES Niacin (vitamin B3)Required for turning foods into energy Meat, fish, poultry, whole and fortified grains, and fortified cereals and maintenance of skin, blood cells, and nervous system CholineNeeded to create signals in brain Liver, milk, eggs, and peanuts and nervous system Pantothenic acid Helps convert food to energy; helpsWidespread in foods, including chicken, beef, oats, cereals, tomato products, (vitamin B5)produce lipids, neurotransmitters, organ meats, yeast, egg yolks, broccoli, and whole grains and hemoglobin Vitamin B6Helps metabolize fats and proteinsPoultry, fish, liver, eggs, whole grains, tofu and other soy products, legumes, oats, and fortified cereals Folate (folic acid)Needed for making DNA in new cells Fortified cereals, dark green leafy vegetables, whole-grain and fortified bread and creating the spinal cord and brain in products, legumes, and orange juice embryos; disposes of homocysteine, a substance that may lead to heart disease Vitamin B12Needed to make new cells and Meat, fish, poultry, milk, cheese, eggs, and fortified cereals prevents anemia (continued)
Table 9.1Micronutrients and Their Food Sources (continued) MICRONUTRIENTBIOLOGICAL FUNCTIONSFOOD SOURCES BiotinHelps convert food to energy and Egg yolks, organ meats, fish, and soybeans break down fats Vitamin CAntioxidant; helps produce collagen; Citrus fruits, broccoli, bell peppers, tomatoes, brussels sprouts, potatoes, aids in iron absorptionstrawberries, cauliflower, and spinach Minerals and Trace Elements CalciumFormation of bones and teeth; also Milk, cheese, yogurt, corn tortillas, some tofu, cabbage, kale, and broccoli blood clotting, muscle contraction, and nerve cell communication ChromiumHelps regulate blood sugar levelsSome cereals, meats, poultry, and fish CopperHelps metabolize ironOrgan meats, seafood, nuts, seeds, wheat bran, whole grains, cereals, and cocoa FluoridePrevents cavities and stimulates Fluoridated water, dental products, teas, and marine fish bone formation IodineComponent of thyroid hormoneIodized salt and some processed foods
MICRONUTRIENTBIOLOGICAL FUNCTIONSFOOD SOURCES IronPart of hemoglobin in blood and Most available form (called hemeform) found in meats and poultry. Non- other enzymesheme form found in legumes, beet greens, artichokes, tofu, dried fruits, and fortified cereals. MagnesiumNeeded ingredient for some chemical Green leafy vegetables, unpolished rice and grains, nuts, meat, reactions in cellsstarches, and milk ManganeseAids bone formation and metabolism Nuts, legumes, whole grains, and teas of proteins, carbohydrates, and cholesterol MolybdenumFactor in metabolism of some proteinsLegumes, grain products, and nuts PhosphorusUsed throughout the body to maintain Dairy products, peas, meat, eggs, and some bread products and cereals pH levels, store and transfer energy in cells, and make DNA SeleniumAntioxidant; regulates thyroid hormoneOrgan meats, seafood, and leafy parts of plants (if selenium is found in soil) ZincComponent of many enzymes Red meats, animal products, whole grains, legumes, and whole-grain and proteinsand fortified cereals
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Vitamin D
Vitamin D is a bit of an oddball among vitamins, because it’s not really part of the diet at all. Humans absorb little vitamin D from food; instead, we synthesize the vast majority of our vitamin D in our skin when we are exposed to sunlight. Vita-min D helps us absorb calcium and phosphorus, the two Vita-minerals that build bones, and for this reason is often added to milk products and calcium supplements. Vita-min D deficiency can lead to a disease called rickets, which is rare in the United States and other industrialized countries today but used to be widespread among poorer children. Because vitamin D can be scarce for babies and toddlers who do not have prolonged sun exposure (which carries the risk of causing skin cancer later in life), vitamin D is the one nutrient that the American Academy of Pediatrics rec-ommends supplementing all children with, from birth through adolescence.
Vitamin E
Vitamin E is one of several antioxidants, a class of substances that act as vigilantes in our cells. Just as the energy production in cars and factories leaves behind waste products that can potentially build up and harm our environment, the energy pro-duction that fuels cells is constantly creating molecules called oxygen free radicals that can cause damage to cells over time. We often think of oxygen as a necessity for life, but when it is attached to various chemicals in our bodies, it can be quite dangerous. Antioxidants scavenge out these extra oxygen molecules and keep them from wreaking havoc in our cells. Vitamin E, one of our primary antioxidant defenders, is found in vegetable oils, wheat germ, nuts, and green leafy vegetables.
Vitamin C
Our dependence on vitamin C was classically demonstrated on ship voyages where sailors often fell ill with scurvy, a painful disease that causes gum bleeding, bruised skin, and difficulty healing. It was finally discovered that stocking up on citrus fruits—or, on many German and Dutch expeditions, sauerkraut—could prevent the disease. Vitamin C contributes to the production of collagen in our tissues, which explains the symptoms of scurvy. It is also a powerful antioxidant and has several functions in the immune system. This vitamin gained a long-standing
pop-ularity in American culture when Nobel laureate Linus Pauling proclaimed that megadoses of vitamin C could ward off the common cold. Though a large body of research has thoroughly debunked that hypothesis, vitamin C is still one of the most popular supplements for children, and the myth is still strong. Unfortunately, vita-min C will do little for your child’s cold. High doses of it are useless anyway, because vitamin C is water-soluble, and the tissues in your body quickly get overloaded with it and dump any extra out in the urine. However, vitamin C is still necessary for health, and it’s important to include foods high in vitamin C in your child’s diet.
Vitamin C is found in citrus fruits and fruit juices, broccoli, bell peppers, toma-toes, brussels sprouts, and many berries.
Vitamin B
6Vitamin B6 is one of the eight water-soluble B vitamins—thiamin, riboflavin, niacin, pantothenic acid, biotin, B6, B12, and folic acid—which all help turn the Vitamins, Minerals, and Dietary Supplements 159
Weaning to Age Three: Special Needs for Growing Bodies
Children triple in size the first three years of life. All of that new bulk doesn’t come from thin air—like a building under construction, children’s growing bodies need a steady stream of raw materials, in this case energy and nutrients in the diet. Because the growth is so rapid, children at this age are particularly vulnerable to dietary deficiencies in vitamins and miner-als. And because their bodies are laying a foundation for their adult selves, these shortages have repercussions that are greater than they would be in adults.
Two of the most important nutrients during this time are iron and zinc. Without iron, infants can develop anemia, and a paucity of zinc can lead to a weak immune system or delayed cognitive development.
Fortunately, breast milk usually provides all the necessary nutrients infants need, and infant formulas are supplemented with iron and zinc to prevent deficiencies. Weaning, with the introduction of a wider variety of foods into the diet, can potentially lead to shortfalls if the new food sources aren’t very rich in nutrients. It’s especially important to choose foods during this time that are high in iron, zinc, and other vitamins, and to feed your infant forti-fied cereals. See Chapter 3 for more hints on nutrition during weaning.
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food we eat into energy and take part in chemical reactions that power the cells of our body. They are often added to fortified cereals and flour, so you probably see them on nutrition labels regularly. B vitamins are found naturally in lots of foods, especially those high in protein. Vitamin B6helps metabolize fats and pro-teins in our bodies. It is one of the most common B vitamin deficiencies in kids.
Nursing moms should also make sure they are eating enough foods with vitamin B6, because the levels of this and other water-soluble vitamins found in breast milk vary depending on a mother’s diet. You can find this vitamin in meats, eggs, whole-grain products, some fortified cereals, bananas, watermelon, prunes, and many vegetables.
Calcium
Children need to consume adequate calcium to build bones and prevent osteo-porosis later in life. (We will discuss this further in Chapter 10.) Calcium is impor-tant during infancy and also later in childhood, because puberty is the time when the body is working most actively to accumulate calcium in bones. Our ability to use calcium in foods also depends on adequate levels of vitamins D and K, and many calcium supplements now include these vitamins. In addition to dairy prod-ucts, calcium is found in dark green leafy vegetables, tofu, dried figs, legumes, oats, and fortified orange juice, and soy milk.
Iron
Iron is used to make hemoglobin, the substance in red blood cells that carries oxy-gen to all the body’s cells and tissues. A lack of iron results in anemia, an insuffi-ciency of oxygen in the blood. Babies who are brought to full term are born with a reservoir of iron from their mothers, but these stores run out in a few months if they are not replaced. Around the time of weaning, babies need to start getting iron from their diet through iron-rich foods and iron-fortified infant cereals. Finding iron in foods can be tricky because it is not always in a form that we can absorb.
The most usable form of iron is found in meats, especially red meat (just like red blood cells, the color red is a sign of iron in animals). Plant foods may be high in iron but in a form that it is harder to absorb. Eating foods that are high in vitamin
C helps with iron absorption; try pairing iron-rich foods with vitamin C–rich foods at snacks and meals. Foods high in iron are meats, legumes, beet greens, artichokes, tofu, dried fruits, and fortified cereals.
Zinc
Many studies conducted in developing countries have documented the need for zinc in the diet. Even a mild zinc shortfall can lead to slower growth in infants and children, and more severe deficiencies can lead to diarrhea, decreased appetite, fre-quent infections, irritability, and possibly even impaired cognitive development.
Zinc is used throughout the body in creating DNA and proteins, and in several components of the immune system. It is crucial that infants have enough zinc for Vitamins, Minerals, and Dietary Supplements 161
Sodium: The Mineral You Don’t Need More Of
In Table 9.1, there is one major mineral I left out: sodium. That’s because sodium is easy to find in foods, and most of us eat much more of it than we need. Most of this extra sodium is simply excreted from the body, but it also pulls water out of the body’s cells, raising blood pressure. It’s not yet clear what effect a salty diet has on children’s long-term health, but over time, high blood pressure can stress the heart and lead to damage of the arteries. A study by the National Heart, Lung, and Blood Institute in adults found that some people who have abnormally high blood pressure can reduce it to normal levels by lowering salt intake—and those who are in the normal range can lower it even further.
The sodium content of natural plant and animal foods is actually quite low, but just about every processed food we eat has salt slipped in somewhere. Processed foods account for most of the sodium that Americans eat. It’s tricky to avoid high-salt foods these days, because many manufacturers know that people on the lookout for sugar, fat, or cholesterol won’t mind if their foods are full of salt. The best way to avoid salt is to limit the processed foods you eat. Avoid cured meats and choose canned foods that say “no salt added,” unsalted nuts, and low- or reduced-sodium versions of condiments and other foods. Use natural spices in cooking instead of salt. And check labels for sodium content before you choose a product.
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Enlisting Good Bacteria for Better Health
One kind of supplement that is used worldwide but still has yet to hit it big in the United States is probiotics, or the use of “good” bacteria in the diet to promote a healthy digestive and immune system. It may sound a little exotic but it’s not—you’re actually using probiotics every time you eat yogurt with live, active cultures. The health benefits of bacteria have been noted since ancient times, but research is finally accumulating to back up the anecdotal evidence.
Think of your digestive system as a vast metropolis teeming with bacteria, and you are a landlord who owns the space they rent. Most of these bacteria are great tenants, and actu-ally help you out in many ways. But others are destructive; they invade and wreak havoc on your property. Getting the right balance of bacteria in your digestive system is crucial to good health. Antibiotics can help destroy an infestation of infectious bacteria, but they leave a lot of collateral damage to the good ones as well. Another tactic is to supply a steady stream of good tenants to crowd out the bad ones and prevent an infection in the first place. This is the basic principle of probiotics: used preventively, they can help ward off potential infec-tions, or used in conjunction with antibiotics during an illness, they can help push the bad bacteria out and establish a healthier balance in your digestive system.
Because the bacteria in probiotics already exist inside us, they are completely benign.
Doctors have used probiotics safely on newborns and infants as a medical treatment many times. Though the jury’s still out on the exact benefits, probiotics have been shown to be helpful in several situations. For one, almost all infants at some time or another are hit with a gastrointestinal infection that leads to diarrhea, usually caused by a rotavirus. Many stud-ies on children hospitalized with this illness have found that supplementing them with pro-biotics decreases the average duration and severity of their diarrhea. Good bacteria have also shown promise in preventing diarrhea that can sometimes crop up in children being treated with antibiotics for common infections. And studies have begun to look at how probiotics
their overall health; fortunately, breast-fed babies almost always get what they need from their mother’s milk, and formulas are generally supplemented with zinc. Dur-ing weanDur-ing, infants should be fed fortified infant cereals and other foods high in zinc. Zinc is most concentrated in animal products, especially red meat, and also in whole grains, nuts, and legumes, and fortified breakfast cereals and infant
cere-als. Zinc is one of the micronutrients you don’t want to get too much of, because extra doses can actually slow the immune system and interfere with iron absorp-tion. Those zinc lozenges you may have seen advertised to treat colds have failed to lessen the length of colds in clinical studies, so they are most likely useless and may even be harmful to children if the dose is too high.
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given to newborns or to pregnant or lactating mothers could prevent or lessen allergies and asthma in children, though the evidence is not yet clear.
As a preventive strategy, it makes sense to use probiotics in situations where your child could be exposed to infections, such as during hospital stays or while attending day care.
Parents in the United States who are interested in giving their children probiotics currently face some challenges. Supplements are your best bet because yogurts, with the exception of those made by Stonyfield Farm, do not carry enough live organisms to be considered true probiotics. And probiotics supplements are afflicted with all the problems of the supplement industry—a lack of regulation and no guarantee that the product contains what it says it does.
Still, you can find some reputable brands in drugstores and health-food stores. Though they often carry a hefty price tag, the best brands guarantee that each pill packs about a billion bacteria (you need to ingest a lot of bacteria to guarantee that enough will survive the trip through your stomach and intestines to have some effect).
While a few different kinds of bacteria are found in probiotics, the type that has been best studied as a supplement is Lactobacillus casei GG. As with any supplement, let your doctor know about any probiotics you intend to use, and keep in mind that they cannot substitute for medical treatment of illness or infection.
European infant formulas now often carry probiotics to mimic the health benefits of live breast milk, and it’s only a matter of time before U.S. versions follow suit. Americans tend to be a little queasier about the idea of ingesting bacteria, though, so companies are focus-ing for now on a related strategy called prebiotics. While not bacteria themselves, these sub-stances are not fully digested in the stomach and small intestine, so they end up in the colon where they serve as food for good bacteria. An example of natural prebiotics is oligosaccha-rides, a type of carbohydrate in breast milk. These are now added to some infant formulas as fructose oligosaccharides or inulin. Though studies have not yet shown prebiotics to have the same impact as ingesting live bacteria, they certainly can’t hurt and may be helpful.