Featured Nutrient: Beta Carotene
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My friend once turned a yellowish tinge after being on a crazy diet where she ate loads of baby carrots. The culprit? Beta carotene, the compound that makes carrots and sweet potatoes orange. (Leafy greens, such as spinach, also contain healthy doses of beta carotene.) In the body, beta carotene is converted to vitamin A, a nutrient essential for healthy vision, immune function and cell growth. It also acts as an antioxidant that neutralizes free radicals.
More carrots, less cancer?
After early research linked diets rich in beta carotene with reduced risk for cancer, scientists supposed that beta-carotene supplements might also help prevent cancer. Unfortunately, two large clinical trials in the 1990s revealed that taking mega-dose beta-carotene supplements increased rates of lung cancer in smokers. Test-tube research shows that, in high doses, beta carotene can act as a pro-oxidant (boosting free-radical production and risk of disease) and this might happen in the body, too, says Robert Russell, M.D., director of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. Skip supplements; eat your veggies, says Russell; "there doesn't appear to be any health risk to getting plenty of beta carotene from foods." (Yellow skin is temporary and harmless, say experts.)
Can beta carotene keep you sharp?
A study in the December 2006 Journal of Gerontology linked high blood levels of beta carotene with a lower risk of cognitive decline in people predisposed to Alzheimer's. "Beta carotene may counter free radical damage involved in the development of Alzheimer's in some people," says Peifeng Hu, M.D., the study's author and an assistant professor at UCLA School of Medicine.
How much?
There's no RDA for beta carotene. Eat plenty of dark green vegetables and orange vegetables and fruits (papaya, mango) weekly to meet your vitamin A needs and reap beta carotene's potential antioxidant benefits.
Featured Nutrient: B12
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Blame it on the law of unintended consequences. As soon as the food industry began to fortify foods like breads and breakfast cereals with folate, nutrition researchers found a new worry. They were concerned that people with vitamin B12 deficiencies—a hidden cause of nerve damage, depression and perhaps even mental decline in older people—might now go undiagnosed. In the past, many cases of B12 deficiency were first recognized when people developed a specific type of anemia that can be caused by either low folate or low B12 levels. Getting extra folate can mask the symptoms of B12-related anemia, making people feel fine even when levels of this crucial vitamin are low enough to cause significant nerve damage.
And then there is the antacid dilemma. B12, which is typically bound up with protein in food, is broken down by stomach acids. The widespread use of antacids for heartburn and gastric reflux has some experts fretting that the pills and liquids could block the absorption of this crucial nutrient. "At the moment we don't really know how serious that issue is," admits University of California-Davis nutrition researcher Lindsay Allen, a leading vitamin B12 expert who helped draft the current federal guidelines. Still, it's clear that a significant percentage of people aren't getting enough. According to one recent survey, 6 percent of Americans are frankly deficient; another 22 percent are borderline deficient.
What it does:
Vitamin B12 is used in making DNA, the building block of genes, and in maintaining healthy nerve and red blood cells. Early signs of trouble include fatigue and dizziness. Over time the consequences of B12 deficiency are more serious, including nerve damage, severe anemia and even dementia. Several studies have linked low B12 levels to depression. Too little may also be hard on hearts. Researchers have discovered that when B12 levels dip, levels of the amino acid homocysteine rise, which is an important risk factor for heart disease.
Older people are most likely to fall short, according to Allen. As we age, the stomach produces less gastric acid, making it harder for the body to absorb B12 from food. Between 10 and 15 percent of people over 60 are thought to be deficient. Because B12 is found mostly in meat and dairy products, some vegetarians and especially vegans may not get all they need.
How much you need:
Most experts think the current recommended daily allowance of 2.4 micrograms a day for people 14 and older provides all the body needs—although some researchers have argued that a daily intake of 6 micrograms would ensure that even people who don't absorb B12 efficiently will get enough. Luckily, it appears you can't get too much B12, as no upper limit has been set. What's more, the body effectively stores the vitamin for a couple of years. So you can fall short now and then and make up the difference later without hardship.
B12 is bound to protein, so foods like meat, fish, eggs and dairy products like yogurt and milk are the principle sources. If you're a vegetarian, it's wise to include plenty of milk, yogurt, or cheese on the menu—and to consider taking a daily multivitamin. If you're a vegan, popping a multi is particularly important. Several brands of multivitamins contain 25 micrograms of B12, more than enough to ensure that you get all you need.
Food sources of B12:
Beef liver, braised (3 oz.) = 60 mcg
Clams, baked or broiled (3 oz.) = 47 mcg
Complete Wheat Bran Flakes (1 cup) = 8 mcg
Nutritional yeast flakes (1 Tbsp.) = 4 mcg
Lobster, steamed (3 oz.) = 3 mcg
Tuna fish, light (3 oz.) = 3 mcg
Salmon, cooked (3 oz.) = 2 mcg
Beef, ground, 90%-lean (3 oz.) = 2 mcg
Milk, 2% (1 cup) = 1 mcg
Cottage cheese, low-fat (1/2 cup) = 1 mcg
Source: ESHA database 2005
Featured Nutrient: Chromium
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After its discovery in the 1950s, chromium languished in relative obscurity. Most people seemed to get plenty of this essential nutrient without giving it a second thought. Now suddenly chromium supplements—usually in a form called chromium picolinate—have become superstars of the dietary-supplement aisle, touted as an easy way to shed fat, build muscles, prevent diabetes and even lower heart disease risk. Is it just hype?
What it does:
Like most such claims, the extravagant promises made for chromium start with a kernel of scientific truth. Chromium is required by the body for the process that turns food into usable energy, helping insulin prime cells to take up glucose. In the 1970s, studies showed that patients given chromium-free intravenous feeding regimens developed abnormal glucose metabolism; once they were given the mineral, the problems vanished.
As Americans and people from other affluent countries began to put on excess pounds and become insulin resistant, however, researchers started to wonder if extra chromium might help give insulin a boost. If so, the mineral could lower the risk not only of diabetes but also heart disease—and might even help some people lose weight.
From the start, the evidence was shaky. Though some studies did show an improvement in glucose metabolism, insulin resistance and cholesterol levels when people took chromium, others turned up no benefit at all. So the National Institutes of Health decided to put chromium to the test. In a study conducted in Boston and in Sydney, Australia, 40 patients with impaired glucose were randomly assigned to one of two groups. Half took an 800-microgram (mcg) chromium pill every day; the others a placebo.
The results, published last year, significantly dimmed chromium's luster. "After three months, chromium didn't improve glucose tolerance, insulin sensitivity or cholesterol levels," says lead researcher Jenny Gunton, Ph.D. And, while the chromium-takers lost a few centimeters around their waists, so did people in the placebo group—belying claims that chromium offers any special help in dropping pounds.
Other findings have tarnished chromium's image as a muscle-building miracle pill. Recent experiments that used the most sensitive methods to measure body fat and lean mass have shown no benefits from popping chromium supplements.
How much you need:
These disappointing findings with supplements don't mean the body doesn't need chromium. Some researchers still believe that falling short may add to the problem of insulin resistance and perhaps diabetes and heart disease. The National Institutes of Health's normal daily recommended intake for adults is 50 to 200 mcg. But because even the same food source can vary widely in how much it contains—and reliable measures of chromium in foods are hard to come by—tallying up your intake can be tricky (see box).
Where to get it:
Best sources of chromium are whole-grain breads and cereals, meat, nuts, prunes, raisins, beer and wine. If those don't show up frequently on your menu, taking a multivitamin/mineral combination, not a chromium supplement, is a wise move. One-a-day multis typically contain 150 mcg—more than enough to give most people all they need to stay healthy.
Food sources of chromium (mcg):
Since there's no large database yet for the chromium content of foods, use these values as a general guide rather than gospel.
Brewer's yeast (1 oz.) = 31.4
Whole-grain bread (1 oz. slice) = 11.8
Broccoli (1/2 cup) = 11.0
Beer (12 oz.) = 9-100
Grape juice (8 oz.) = 7.5
Turkey ham (1 oz. slice) = 3.5
Beef (3 oz.) = 2.0
Adapted from the Linus Pauling Institute, Oregon State University, and www.healthyeatingclub.orgFeatured Nutrient: Vitamin K
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Vitamin K? What, you might well ask, ever happened to vitamins F, G, H, I and J?
In fact, when Danish researcher Henrik Dam discovered a substance essential to blood clotting in 1929, he jumped right over the intervening letters of the alphabet and named his new find vitamin K, for koagulation. For years afterwards, coagulation seemed to be the vitamin's only function. But now researchers are turning up evidence that vitamin K plays other crucial roles in the body, prompting some scientists to think the optimal intake may be higher than current guidelines recommend.
What it does:
Vitamin K is used by the body to produce an array of different proteins. Some of them are used to create factors that allow blood to coagulate—critical in stemming bleeding and allowing cuts and wounds to heal. Other vitamin K-dependent proteins are used for maintaining healthy bones and keeping arteries unclogged. "Vitamin K allows a protein called osteocalcin to bind to calcium in bone, for example, which helps maintain bone density," explains Sarah L. Booth, Ph.D., a scientist at the USDA Human Nutrition Research Center on Aging at Tufts University and one of only a small group of vitamin K nutrition experts in the world. There's also preliminary evidence that vitamin K-dependent proteins may have a role in preventing hardening of the arteries, which can constrict blood flow and trigger heart attacks.
How much you need:
The current recommended daily intake of vitamin K is 90 micrograms for women and 120 for men, based on the levels that are needed to maintain normal coagulation, and currently there is no set upper level intake. Booth and other experts suspect that the most effective level may be higher, based on what is being discovered about K's other roles. "At the moment, though, we don't have the data to say exactly what optimal intake should be," she admits.
Luckily, vitamin K deficiency is extremely uncommon. And since the main dietary sources of vitamin K are dark green vegetables, which are healthy for many reasons, the best advice is to help yourself to as much as you can. In a 10-year study of 72,000 women enrolled in the Nurses' Health Study, researchers found that those who consumed the most foods containing vitamin K had a 30 percent lower risk of hip fractures than those whose diets contained the least vitamin K. Whether the vitamin itself or other nutrients in the foods were responsible for the benefit isn't known. But in a small 2002 study at Osaka Medical College in Japan, researchers found that vitamin D and K supplements increased bone density in postmenopausal women.
Leafy green vegetables of all kinds, from spinach and kale to arugula and green leaf lettuce, are especially rich in the vitamin. "In plants, vitamin K is involved in photosynthesis, so an easy rule of thumb is the greener the leaf, the more vitamin K it contains," says Booth. Spinach has a lot, for example; pale iceberg lettuce much less. Vitamin K is also abundant in many vegetable oils, including soybean, canola, and olive oil.
A word of caution:
If you are taking an anticoagulant medication such as warfarin, your doctor may advise you to avoid overdoing foods rich in vitamin K, since the vitamin can interfere with the drug's action. If you have any questions, talk to your doctor before making changes to your diet.
Food Sources of Vitamin K:
Kale, cooked (1/2 cup) = 531 mcg
Spinach, raw (1 cup) = 145 mcg
Broccoli, cooked (two 5" spears) = 104 mcg
Asparagus, cooked (1/2 cup) = 68 mcg
Arugula, raw (1 cup) = 62 mcg
Green leaf lettuce (1 cup) = 57 mcg
Soybean oil (1 Tbsp.) = 27 mcg
Canola oil (1 Tbsp.) = 17 mcg
Olive oil (1 Tbsp.) = 8 mcg
Tomato, fresh (1 med.) = 7 mcg
Featured Nutrient: Potassium
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The word "ubiquitous" comes to mind with potassium, a mineral found in all the body's cells as well as in the fluid surrounding them. It's involved in almost every vital body process: maintaining blood pressure, heart and kidney function, muscle contraction, even digestion. And we humans were obviously meant to get plenty of it, since it's abundant in just about any fresh, whole food—from potatoes and peas to milk and fish.
Why, then, do surveys show that most Americans get less than half the recommended amounts of potassium?
Problem is, say experts, we haven't been eating many of those whole foods lately. When a food is processed—"whether it's cooked or put in a can, you lose potassium," explains R. Curtis Morris, Jr., M.D., a nephrologist at the University of California at San Francisco and a member of the advisory panel on Dietary Reference Intakes. Matters worsen when manufacturers add salt during processing, as they almost always do: when we eat those foods, we deplete our potassium stores to help us handle the excess sodium. Many researchers feel that the resulting sodium-potassium imbalance is one reason why the U.S. incidence of hypertension (high blood pressure) keeps climbing, —and with it, our risk of diseases related to blood pressure, notably stroke.
What would happen if we got enough?
If Americans increased their potassium intake to meet recommendations, says Morris, "we'd readily reduce the likelihood of people expressing hypertension." For evidence, we need look no farther than the DASH (Dietary Approaches to Stop Hypertension) and Omni Heart trials—major studies in which people with confirmed or near hypertension saw significant drops in their blood pressure after eating a potassium-rich diet that included 9 to 10 daily servings of fruits and vegetables and ample amounts of low-fat dairy products.
More potassium would likely benefit our bones and kidneys too, says Morris, who is one of many who believe that our protein- and cereal-grain-rich western diet produces more acid than our bodies were designed to handle. Excess acid in the blood causes calcium and other minerals to leach out from bones to buffer it, causing bone loss and encouraging the formation of calcium-containing kidney stones. Potassium-rich foods, on the other hand, are alkaline, so eating more of them might help counterbalance this tendency, thus helping to preserve bones and prevent kidney stones.
How much you need—and how to get it
Because of potassium's health benefits, the recommended adequate intake of potassium for teens and adults is 4,700 milligrams (mg) daily. (The exception are people with kidney disease or severe congestive heart failure, who may have trouble getting rid of the mineral and must limit their intake.) While getting enough potassium through foods is doable, Morris readily admits it takes plenty of fresh fruits, vegetables and "organization" to pull it off. Those who have trouble can ask a doctor to recommend a potassium citrate or malate supplement.
The best potassium sources are foods that are closest to their original states, so be sure to choose whole, unprocessed foods as often as possible, especially fruits and vegetables, low-fat dairy products, whole grains, fish and lean meats. If that sounds familiar, it should; it's how nutrition guidelines have urged us to eat for years. Add potassium to the many compelling reasons why it's worth the effort.
Food sources of potassium (MG):
Sweet potato, baked, 1 medium = 694
Beet greens, 1/2 cup cooked = 655
Potato, baked, 1 medium = 610
Yogurt, plain, nonfat, 1 cup = 579
Halibut, cooked, 3 oz. = 490
Lima beans, 1/2 cup cooked = 484
Banana, 1 medium = 422
Milk, nonfat, 1 cup = 382
Cantaloupe, 1/4 medium = 368
Orange juice, 3/4 cup = 355
Source: U.S. Dietary Guidelines 2005
Featured Nutrient: Magnesium
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Long a wallflower in the field of nutrition, magnesium has recently drawn rapt attention. Harvard just released a study of almost 130,000 men and women reporting that those who consumed more magnesium in their diets were less likely to develop type 2 diabetes. Other studies show that it may reduce the risk of coronary heart disease and stroke.
Although crucial to health, magnesium has been sorely neglected by the American diet; some studies suggest that three-quarters of the population fail to get enough. Interestingly, even small increases in dietary magnesium helped lower the chances of diabetes, says researcher Ruy Lopez-Ridaura. Supplements, however, had no effect.
What it does:
Necessary for some of the body's most basic processes, magnesium triggers more than 300 biochemical reactions—most importantly the production of energy from the food we eat. It also generates a response to insulin, the hormone that ushers glucose into the body's cells, where it is used to make energy. It help make proteins in the body, maintains muscle and nerve function, sustains a steady heart rhythm, regulates blood pressure, and keeps bones and teeth strong.
How much you need:
Most Americans take in far less than the RDA of magnesium, says Lopez-Ridaura. "People should try to get around 300 mg/day (women) and 350 mg/day (men) to have an important reduction in their risk of diabetes." But too much supplemental magnesium is also not recommended, the National Nutrition Board has set the upper limit for supplemental magnesium at 350 mg.
Food sources of magnesium:
The mineral is abundant in avocados, nuts and leafy greens. "Magnesium is also very closely associated with fiber and whole grains," Lopez-Ridaura notes. "When grains get processed and refined, they lose a lot of magnesium. Western diets in general are bad for diabetes, and lack of magnesium could be one explanation of this increasing epidemic."
1 cup baked acorn squash = 105 mg
1 oz. toasted wheat germ = 90 mg
1 oz. dry-roasted almonds (24 nuts) = 86 mg
2 rectangular biscuits shredded wheat = 80 mg
1/2 cup cooked spinach = 65 mg
1 stalk broccoli = 59 mg
1 medium kiwi fruit = 23 mg
1/2 medium Hass avocado = 103 mg
Featured Nutrient: Vitamin C
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Vitamin C burst into prominence back in the 1970s, when Nobel Prize-winning scientist Linus Pauling claimed that high doses could stop cancer and might be the long-sought cure for the common cold.
Alas, neither claim has quite held up under scrutiny. Vitamin C doesn't prevent colds. Nor does taking large doses slow or stop cancer. But Pauling's instincts were not entirely wrong. There are still many sound reasons to get plenty of C.
What it does:
Researchers have long known that vitamin C is an essential building block of collagen, the structural material for bone, skin, blood vessels and other tissue. Failing to get enough vitamin C causes inflammation of the gums, scaly skin, nosebleed, painful joints and other problems associated with scurvy.
In addition, many studies show that eating foods rich in C can reduce the risk of developing cancer, particularly cancers that strike the mouth and digestive tract, according to Jane Higdon, a nutrition scientist at the Linus Pauling Institute at Oregon State University. Vitamin C is a potent antioxidant, able to neutralize unstable oxygen molecules that might otherwise damage DNA. Recent findings suggest it may also protect against Helicobacter pylori, bacteria linked to both stomach cancer and ulcers. A 2003 study at the San Francisco Veterans Affairs Medical Center reported that people with high blood levels of vitamin C are less likely to test positive for infection by H. pylori. The vitamin appears to inhibit bacterial growth.
Vitamin C is also proving to be friendly to the heart and arteries. Analyzing data from more than 85,000 women in the Nurses Health Study, researchers at Children's Hospital, Boston, reported in 2003 that those with the highest intake of C had the lowest risk of heart disease over a 16-year period. Here, too, the antioxidant effect may be at work, preventing damage to artery walls that can promote cholesterol buildup. But vitamin C seems to protect in other ways as well. In 2004, scientists from the University of Oslo reported that after volunteers ate two or three vitamin-C-rich kiwis a day for 28 days, platelets in their blood were less likely to clump together and form small blood clots that can jam arteries and lead to heart attack or stroke. Eating kiwis also lowered triglycerides, or fats in the blood, by 15 percent, an effect that scientists credit to kiwis' vitamin C, E and polyphenol content.
Getting plenty of C may be especially important for pregnant moms and infants. Last year a study in Seoul, South Korea, reported higher birth weights among babies born to mothers with high vitamin C levels. This year a report in the European Journal of Clinical Nutrition suggests that vitamin C in breast milk may reduce the risk of allergic dermatitis in predisposed infants.
How much you need:
The current recommended daily intake for men is 90 mg and for women it is 75 mg. "Don't waste your money on megadoses of vitamin C," says Higdon. A National Institutes of Health study showed that the body can only absorb a maximum of about 400 milligrams a day; more than that simply washes out of the system (the upper tolerable limit for vitamin C has been set at 2,000 milligrams per day). Follow the latest advice to eat between five and nine servings of fruits and vegetables a day and chances are you'll get all you need—especially if you choose several foods high in C.
Food Sources of Vitamin C:
Virtually everything in the produce section boasts some vitamin C. Excellent sources (per 1/2 cup serving) include:
green bell pepper = 60 mg
orange = 48 mg
strawberries = 45 mg
broccoli = 39 mg
cantaloupe = 29 mg
tomato = 23 mg
turnip greens, cooked = 20 mg
sweet potato, baked with skin = 20 mg
okra, cooked = 13 mg
Featured Nutrient: Vitamin D
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By all rights, vitamin D should be the one essential nutrient we don't need to fret about. During the summer months, most of us need only about 10 to 20 minutes of direct sun on the hands and face for our skin to manufacture enough D for the whole day. To make up for any shortfall, especially in young children, milk has been fortified with D since the 1930s.
So it came as a shock a few years back when surveys found that a large number of Americans aren't getting nearly enough. In one study, for example, 32 percent of healthy young adults in Boston were found to be vitamin D-deficient.
What it does:
Early on, most of the concern focused on bones, since vitamin D, working along with calcium, helps build and maintain them. But now there are new worries. "Receptors for vitamin D are being found on all kinds of cells where we never expected to find them," says Hector DeLuca, M.D., professor and chair in the department of biochemistry at the University of Wisconsin-Madison. "That suggests it plays a much broader role in the body than we imagined." In fact, vitamin D regulates more than 50 different genes, affecting tissues throughout the body. Falling short may be risky in ways scientists never suspected.
The first disease to be linked to vitamin D deficiency was rickets, which occurs when children's bones don't get enough calcium to form normally. In adults, a shortfall in D can lead to soft and painful bones because D plays a crucial role in maintaining steady levels of calcium in the blood.
New investigations are turning up other essential functions: maintaining the immune system, controlling blood pressure, and ensuring the secretion of insulin in order to control blood-sugar levels.
Studies show that too little vitamin D is associated with a greater risk of several autoimmune diseases, including multiple sclerosis and rheumatoid arthritis. Last year, researchers at the Harvard School of Public Health reported that women who got at least 400 international units of vitamin D daily—the amount found in the typical multivitamin supplement—were 40 percent less likely to get MS than those not taking multivitamins.
Inadequate levels have also been linked to increased danger of several cancers, including colon and prostate cancer, and both insulin resistance and metabolic syndrome, the constellation of conditions that dramatically increases heart-disease risk.
How much you need:
Guidelines on vitamin D are currently under debate. The official recommendations now call for 200 international units for children and 600 IU for people over 71, with other groups falling somewhere between. But many researchers reviewing the latest findings think most adults should be getting around 1,000 IU per day and some suggest even dramatically higher levels. Currently the safe upper limit is 2,000 IU, and until new recommendations are issued, people should not exceed this level unless taking the supplement under doctor supervision; too much vitamin D can be toxic.
One way to boost vitamin D levels is simply to catch some rays when the sun is high without putting on sunscreen. But that advice is extremely controversial, since too much unprotected sun exposure can cause skin cancer. And there's another problem. "In the northern part of the country, the sun isn't strong enough in the winter months to trigger vitamin D production," says DeLuca, even if you are crazy enough to sunbathe on a rooftop in Boston in December.
Food sources of vitamin D:
We rely on fortified milk and breakfast cereals to get most of our dietary vitamin D-an 8 ounce glass of milk has 100 IU. And apart from a few kinds of fish that are naturally rich in D, including herring and sardines, there aren't many natural food sources. "That leaves supplements," says DeLuca. Like a growing number of experts, he thinks supplements, especially during winter and spring when people are most likely to be deficient, are a good idea. Standard multivitamins contain 400 IU. If you don't drink much milk, it might be worth taking an additional 400 IU through a vitamin D capsule.
Featured Nutrient: Folate/Folic Acid
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Long linked to the health of pregnant women and their infants, folate is growing in repute. Physicians now prescribe diets rich in folate and folic acid, its synthetic equivalent, to patients at risk for heart disease and stroke. Recent studies also suggest that this B vitamin may keep depression and certain cancers at bay.
What it does:
Folate is necessary for the production of new cells, including red blood cells. Fortification of grain products like cereals and flour in the U.S. began six years ago, but experts say that folate deficiency remains a major cause of spinal-cord defects in newborns. Estimates vary, but by one count the average American woman is getting only 278 micrograms of folate a day, far below the recommended 400 mcg. If you are deficient in folate, you are also likely to have higher levels of homocysteine in your blood, a risk factor for heart disease and stroke. In one study, 800 mcg of folate per day reduced the risk of heart disease by 50 percent in nondrinkers. Other studies have shown that correcting a folate deficiency can sometimes reverse depression.
How much you need:
Many dietitians recommend taking a multivitamin with 400 mcg of folic acid (1,000 mcg per day is the safe upper limit for folic acid, which in excess can mask a vitamin B12 deficiency). People over age 50 taking folic acid are advised to take a supplement balanced with vitamin B12.
Food sources of folate:
Rich sources of folate include liver, dried beans and peas, spinach and leafy greens, asparagus and fortified cereals.
Kidney beans (1 cup cooked) = 230 mcg
Lentils (1 cup cooked) = 358 mcg
Asparagus spears 6 each = 134 mcg
Oatmeal (fortified) = 130 mcg
Spinach (1/2 cup cooked) = 121 mcg
Romaine lettuce (1 cup chopped) = 76 mcg
Peas (1/2 cup cooked) = 47 mcg
Featured Nutrient: Zinc
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Complain of a head cold and stuffy nose and chances are some well-intentioned acquaintance will suggest a zinc lozenge, the very supplement that male would-be swingers were popping in the '70s to increase bedroom stamina. For a trace mineral, needed in only tiny amounts, zinc has garnered a lot of attention in recent years. Much of it is well deserved, although surprisingly not for the reasons many suspect.
What it does:
Zinc is integral to almost every cell of the human body, it keeps the immune system healthy, helps heal wounds, aids in breaking down carbohydrates, fats and proteins, maintains the body's keen sense of both taste and smell, regulates testosterone and supports the body in growing and developing properly. In addition, scientists continue to investigate the role that zinc may play in preventing prostate cancer and diabetes, in regulating male fertility and in warding off macular degeneration—an age-related condition that can lead to blindness. As for preventing the common cold and enhancing sexual prowess, current research suggests that any benefit may stem more from a placebo effect than a true remedy, although the jury is still out on whether zinc can help shorten the duration of a cold. Health professionals are quick to warn, however, that people can easily harm themselves by taking too much supplemental zinc.
Although zinc is readily available through diet, about 20 percent of men and 40 percent of women in this country fail to get enough. True zinc deficiencies are rare in the United States, but health researchers are finding that low levels have a multitude of consequences: difficulty healing wounds, diminished appetite, low birth weight, possible infertility in men, muscle fatigue and diminished strength.
One study recently showed that young men's muscle strength and endurance dropped when they ate a low-zinc diet (4 milligrams/day) for 9 weeks, compared to a similar time period when they consumed a higher-zinc diet (15 mg/day). According to the researcher, Hank Lukaski, a physiologist at the USDA Human Nutrition Research Center in Grand Forks, North Dakota, zinc activates an enzyme that helps the body shed carbon dioxide, which is produced when we burn carbohydrates and fat. A buildup of carbon dioxide will cause the cells to malfunction, and make even simple physical chores more difficult. "We're talking about normal activities, nothing more than someone carrying two shopping bags out of the grocery store," Lukaski says.
How much you need:
As essential as zinc is, you don't need much for a healthy body. The recommended dietary intake for men is 11 mg/day, for women 8 mg/day (11 and 12 mg, respectively, if pregnant or lactating). Adolescents and the elderly are two populations at risk of getting too little zinc. Strict vegans, who don't eat meat, dairy or eggs, should also keep an eye on their zinc intake.
But unless you have a health condition that warrants zinc supplementation, most health professionals advise against it. While a balanced vitamin/mineral supplement is fine, too much zinc, near the upper limit of 40 mg/day and above, may affect the body's ability to absorb and store calcium and copper, and may eventually lead to a debilitating anemia.
Food Sources of zinc:
It's easy to enter the danger zone with supplemented zinc, so dietitians encourage most people to depend on diet instead. Oysters offer a particularly rich source, but lean red meats and chicken, along with legumes, whole grains and dairy products, also pack a tidy sum.
Oysters, steamed (3 oz.) = 30.0 mg
Cooked beef tenderloin (3 oz.) = 4.8 mg
Turkey, dark meat, roasted (3 oz.) = 3.9 mg
Chickpeas (7 oz.) = 2.8 mg
Roast chicken leg = 2.7 mg
Pumpkin seeds (1/4 cup) = 2.6 mg
Cooked pork tenderloin (3 oz.) = 2.5 mg
Plain low-fat yogurt (1 cup) = 2.2 mg
Wheat germ (2 Tbsp.) = 1.8 mg
Tofu (4 oz.) = 1.7 mg
Dry roasted cashews (1 oz.) = 1.6 mg
Swiss cheese (1 oz.) = 1.0 mg
Featured Nutrient: Vitamin E
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Caught in a quandary about how to handle vitamin E, consumers who have taken hefty doses for years are now rethinking their approach to the potent antioxidant. While research from the past decade claimed that vitamin E may prevent a litany of chronic diseases, other researchers argue that no strong evidence exists to support the claim; a new review of 19 studies contends that taking 400 international units (IU) or more of the vitamin per day might increase the risk of mortality. What's a conscientious consumer to do? For now, say many health professionals, stick to the natural delivery system of vitamin E: food.
What it does:
Scientists have not yet elucidated all of vitamin E's roles, but they hypothesize that it has a role in immune function, DNA repair, the formation of red blood cells and vitamin K absorption. They have confirmed that vitamin E acts as an antioxidant, particularly in protecting cell membranes from damage.
The debate lies in whether supplements can prevent future illness, and many observational studies have in fact linked vitamin E to a reduced risk of heart ailments, cataracts and Alzheimer's disease, as well as an improvement in immune function. Laboratory studies have also discovered that the vitamin can kill certain cancer cells.
But many scientists point to the fact that large-scale, randomized clinical trials—the gold standard of experiments—have yet to observe these benefits. Claus Schneider, a biochemist at Vanderbilt University, points out that aside from possible dangers, synthetic vitamin E supplements do not provide the same mix of alpha, beta, delta and gamma compounds found in natural foods (however, alpha tocopherol is the most biologically active form).
How much you need:
The RDA in men and women is 23 IU, or 15 milligrams, and because many E-rich foods come from nuts and oils, some low-fat diets may be inadequate in vitamin E. Because most foods have small amounts of vitamin E it's virtually impossible to get too much vitamin E through food, and some people may find it difficult to achieve the recommended dietary allowance through diet alone. As insurance, you may want to take a multivitamin that provides 100 percent of the vitamin E requirement, but use caution with high-dose supplementation- the upper tolerable limit for the vitamin is set at 1000 milligrams alpha tocopherol.
Food Sources of Vitamin E:
1 Tbsp. wheat germ oil = 20 mg
1/4 cup sunflower seeds = 12 mg
1 cup cooked spinach = 7 mg
1 ounce almonds (23 nuts) = 7 mg
1 Tbsp. safflower oil = 5 mg
1 ounce hazelnuts (21 nuts) = 4 mg
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