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Choosing a Multivitamin

by Marie Spano, M.S., R.D.

A good diet can supply most if not all of the vitamins and minerals you need. But maintaining such a diet day in and day out can be a challenge, which is why many people take a daily multivitamin–multimineral supplement as a form of insurance. Taking a daily supplement makes particular sense for people who don't eat much, such as people who are following a weight-loss diet. While a supplement can't supply all of what is present in fruits, vegetables, and whole grains, such as fiber and phytochemicals (healthy plant chemicals that may help fight cancer and other diseases), it can help to fill in some of the holes.

The question then is how to choose a supplement that meets your needs. Which vitamins and minerals should it contain, and how much?

What and how much
Most people should look for a supplement that contains 100% Daily Value (%DV) of each of the following vitamins and minerals:

• Vitamin A (preferably in the form of beta-carotene)
• Folic acid
• Niacin
• Vitamin B1 (thiamine)
• Vitamin B2 (riboflavin)
• Vitamin B6
• Vitamin B12
• Vitamin C
• Vitamin D
• Vitamin E
• Copper
• Zinc

Premenopausal women should additionally look for a supplement that contains 100% DV for iron (18 milligrams), but postmenopausal women and men are generally advised to take no more than 8 milligrams of iron daily, and some people may be advised by their physician to take no supplemental iron.

People with diabetes may additionally want to look for a supplement that contains 100% DV for chromium and at least 25% DV for magnesium. (Multivitamins never contain 100% DV for magnesium because it won't fit into a single pill.)

To quickly find a multivitamin–multimineral supplement that contains at least 100% DV of at least two-thirds of the nutrients it contains, look for the words "high potency" on the label. This label term is regulated by the U.S. Food and Drug Administration.

Is more better? Not necessarily. Taking more can be harmful in some instances or just a waste in others. Though many people take extra vitamins and minerals in the hopes of preventing cancer and other chronic diseases, the research is mixed regarding the use of supplemental vitamins and minerals for this purpose.

Some companies sell special supplement formulas targeted toward seniors, women, men, or other particular groups. However, it is up to the company itself to decide what to put in each of those formulas. There is no standard definition or regulation determining what should go into a specialized formula. And some of these targeted formulas may fall short on certain vitamins and minerals, including those especially necessary for the exact age group or sex they are targeting! Before you buy a supplement that claims to meet the needs of a specific group, read the bottle yourself and evaluate whether it really provides what you need.

What the numbers mean
The %DVs found on supplement labels are based on the Dietary Reference Intakes (DRIs) established by the Food and Nutrition Board of the National Academy of Sciences and Health Canada. The DRIs are a set of recommended intakes of nutrients for individuals according to their age and sex and may be stated as recommended dietary allowance (RDA) or adequate intake (AI).

The RDA is the amount of a vitamin or mineral found to be sufficient to meet the nutrient requirements of nearly all (98%) individuals in a group. AI is used in cases where RDAs haven't been established because of insufficient data. AI is the amount believed to cover the needs of all individuals in a group.

A third set of numbers, the Tolerable Upper Intake Level (UL) is the amount of a nutrient above which the risk of adverse effects and toxicity increases. The UL represents vitamin or mineral intake from all sources, including food, water, and supplements.

DRIs have been established for 22 distinct life stage and gender groups. The %DV, while based on these numbers, combines many of these life stage and gender groups and excludes pregnant and lactating women to come up with numbers that apply to a wide population. For a list of all DRIs for each vitamin and mineral based on age and sex, go to www.iom.edu.

Special ingredients
Many supplements contain additional, sometimes exotic ingredients (such as herbs or particular antioxidants) for a premium price. It is often unclear whether these ingredients offer benefits at all or, if they may have benefits, whether they offer them in the form they are found in, such as a tablet, pill, or capsule. Don't pay a premium for a few additional ingredients in a multivitamin. Instead, make a point of eating a wide variety of fruits and vegetables, and you are bound to get the antioxidants that will help ensure good health.

Testing supplements
The letters "USP" on a supplement label mean that the tablets meet the voluntary standards of the U.S. Pharmacopoeia and that they dissolve in a lab test designed to mimic what happens in your gut. A product with USP on the label is an added benefit. Manufacturers can also voluntarily pay to have their product tested for quality, purity, disintegration, and dissolution. For more information on testing, try the following Web sites:

• Council for Responsible Nutrition: www.crnusa.org
• NSF International, the Public Health and Safety Company: www.nsf.org
• United States Pharmacopeia: www.usp.org
• Consumer Lab: www.consumerlab.com

Form and timing
Although it is probably best to space your vitamin and mineral intake throughout the day for maximum absorbability, taking 3–4 pills per day just to get your daily dose isn't very realistic for most people. If that's the case for you, choose a brand that contains what you need in one pill. (This may not be possible for calcium supplements, which should contain no more than 500 milligrams per supplement.) If large pills are hard for you to swallow, go with chewable, liquid, or powder forms of vitamins.

In general, you should take vitamin and mineral supplements with a meal, since many nutrients are better absorbed when taken with food. However, if you have also been told to take any medicines with your meals, speak to your dietitian or another health-care provider about when to take vitamin and mineral supplements. Medicines should generally be taken a few hours apart from any supplements, just in case the two could interact. Iron, in particular, is known to have possible interactions with antacids, calcium supplements, and antibiotics and must be taken one to two hours apart from these substances.

Vitamins
Vitamins are necessary to ensure proper functioning within the body. Vitamins act as coenzymes, ensuring the proper functioning of enzymes.

Vitamin A. Vitamin A is best known for its role in helping the eyes adjust when going from brighter to dimmer light, so that a person can see well in the dark. But it has other roles, as well. It helps promote cell and tissue growth throughout the body and protects skin and other tissues from infection. The carotenoid form of vitamin A, found in plant foods, also functions as an antioxidant.

Multivitamins should contain vitamin A in the form of beta-carotene, which the body converts to vitamin A. Though large doses of vitamin A are stored in the body and are toxic, beta-carotene is not toxic, though high doses (33,000–50,000 IU) may raise the risk of lung cancer in smokers.

B vitamins. The B vitamins, which include biotin, choline, folic acid, niacin, pantothenic acid, B1, B2, B6, and B12, are involved in the metabolism of carbohydrate, fat, and protein and in energy production. Because the B vitamins work together, single sources of a particular B vitamin should not be taken unless prescribed by a physician.

Although deficiencies in most of the B vitamins are not common, taking excess amounts of folic acid can mask a B12 deficiency. A deficiency of either can lead to anemia. People who eat absolutely no animal products (vegans) and who do not take a multivitamin supplement are at risk for B12 deficiencies. Also at risk of a B12 deficiency are people who do not have a protein typically found in the stomach lining called intrinsic factor, which is necessary for the body to absorb B12. These people must receive B12 in shots. The elderly are also at risk for developing a B12 deficiency because their bodies are more likely to stop producing intrinsic factor. For this reason, elderly people should take a multivitamin supplement unless otherwise directed by their physician.

Vitamin C. Vitamin C is well known for its role in immune functioning. However, it also helps produce collagen, keeps capillary and blood vessel walls firm, thereby preventing bruising, keeps skin and gum tissue healthy, and helps the body absorb plant sources of iron (non-heme iron; a form that is not well absorbed overall).

Vitamin D. Vitamin D helps the body absorb both calcium and phosphorus. In addition to obtaining vitamin D from food and beverages, the body can manufacture the active form of this vitamin in the body upon exposure to sunlight.

Vitamin D has been in the news lately due to recent research examining vitamin D intake and a reduced risk of colon, breast, and prostate cancer, as well as research indicating that certain groups of individuals may be deficient in vitamin D. Those likely to be deficient include people living in less sunny climates (especially during the winter) and the elderly (the body's ability to synthesize vitamin D from sunlight decreases with age).

Vitamin E. Vitamin E's main function is as an antioxidant, protecting cells from damage. Vitamin E is actually a group of eight compounds, all with different potencies. Within each one of these eight compounds, there are several forms, called stereoisomers. Vitamin E is one particular micronutrient for which it is near-impossible to meet your daily needs through food intake alone (unless that food is fortified with vitamin E), so supplementation is a viable option. If possible, choose a supplement that contains "mixed tocopherols and tocotrienols." Supplementation with the main form, found in supplements containing alpha-tocopherol, decreases tissue stores of one of the other forms, gamma-tocopherol.

If you take any form of blood thinners or anticoagulant medicines, make sure your doctor knows that you are taking a supplement that contains vitamin E.

Vitamin K. Vitamin K plays a vital role in blood clotting. It also helps the body make proteins for the blood, bone, and kidneys.

If you are taking blood thinners or anticoagulants, check with your doctor if you plan on taking a vitamin supplement that contains vitamin K.

For more information about these vitamins, check out the chart "Vitamins."

Minerals
Minerals help regulate several body processes such as fluid balance, muscle contractions, and nerve impulses. Some minerals help make up the structural integrity of bones and teeth.

Calcium. Calcium is best known for its role in keeping bones and teeth strong. However, it also plays a vital role in muscle contractions, blood vessel contraction and expansion, the secretion of hormones and enzymes, and sending messages through the nervous system.

The amount of calcium absorbed decreases as the amount of calcium consumed at one time increases. Therefore, it is best to take 500 mg or less at one time.

Chromium. Chromium is involved in the metabolism of fat, protein, and carbohydrate. In addition, it can enhance the action of insulin. In fact, chromium deficiency can impair the body's ability to use glucose. Consequently, there has been a considerable amount of interest in the possibility that supplemental chromium may help minimize the impaired glucose tolerance associated with Type 2 diabetes. However, there have been no large, randomized, controlled clinical trials carried out in the United States to support this hypothesis. In fact, a review of 15 trials revealed that all but one showed chromium supplementation had no effect on glucose or insulin concentrations in people with or without diabetes.

Both the safety and efficacy of chromium supplementation for people with diabetes is considered controversial. In addition, researchers are still trying to elucidate which form of chromium has the best absorbability. At this point, therefore, most health organizations recommend taking a daily supplement that has no more than 100% DV or speaking to your physician before taking more.

Copper. Copper plays a role in the functioning of several enzymes, helps the body make hemoglobin (which transports oxygen throughout the body), and helps the body produce energy in the cells. A very high intake of zinc can interfere with the absorption of copper.

Iron. Iron is essential for both the functioning and synthesis of hemoglobin. It is also involved in DNA synthesis, immune functioning, brain development, and the synthesis of neurotransmitters and collagen.

Check with your physician prior to supplementing with greater than the RDA for iron. If you take antacids or other calcium-containing supplements, take your iron supplement one to two hours before or after. Take iron two hours before or after any antibiotics.

Magnesium. Magnesium is part of over 300 enzymes that regulate bodily functions, including energy production, muscle contraction, and the manufacturing of body proteins. Magnesium is also a structural component of bones. Single-dose multivitamin–multimineral supplements do not contain 100% DV of magnesium because that quantity of magnesium will not fit into one pill.

There is some indication that Americans may not get a sufficient amount of magnesium from their food. Making a conscious effort to eat more high-fiber foods, which are often rich in magnesium, may remedy this problem. Good dietary sources of magnesium include legumes (dried beans and peas), nuts, whole grains, and green vegetables.

Magnesium-based supplements have been marketed to people with diabetes as a result of research indicating that higher magnesium intake is associated with lower fasting insulin concentrations in both adults and obese children. Lower fasting insulin levels may correspond with greater insulin sensitivity and possibly even a decreased risk of developing Type 2 diabetes. In addition, low magnesium levels have been noted to occur in approximately 25% to 38% of people with Type 2 diabetes. However, clinical studies in which magnesium supplements were given to people with Type 2 diabetes in an effort to decrease their fasting blood glucose levels and improve insulin sensitivity have yielded mixed results.

Though magnesium seems to be related to insulin action, individual magnesium supplements should only be taken if a physician recommends it. Otherwise, a multivitamin–multimineral supplement with a bioavailable source of magnesium (see the chart "Minerals") and plenty of magnesium-rich foods is the safe option.

Potassium. Potassium helps regulate fluid and mineral balance, maintain normal blood pressure, and transmit nerve impulses and helps your muscles contract. The amount of potassium in multivitamin–multimineral supplements is minimal, and the majority of people should obtain enough from food sources. Many fruits and vegetables, including tomatoes, potatoes, oranges, strawberries, and melon, are high in potassium.

Zinc. Zinc is essential for cell reproduction, immune functioning, and tissue growth and repair. It is essential for growth and helps the body use carbohydrate, protein, and fat.

Iodine, manganese, molybdenum, chloride, boron. All of these minerals are found in food, and supplementation isn't necessary.

Individualized intake
Certain people have increased nutrient needs. These include women who are pregnant or breast-feeding, people with certain diseases, elderly people, vegans, people on restricted diets or low-calorie diets, and people who do not eat a healthy diet rich in fruits, vegetables, whole grains, and low-fat meat, poultry, and dairy products. If you have any questions about whether you should be taking additional vitamins or minerals, speak to your health-care provider. Though we know the general functions of each vitamin and mineral, research is ongoing, and scientists are continually learning more about how certain vitamins and minerals play many different roles in our body, preventing disease and promoting good health. In the meantime, do what you can to ensure your good health by following a healthy diet and taking a daily multivitamin–multimineral supplement with approximately 100% DV of most vitamins and minerals.

Marie Spano is a registered dietitian and exercise physiologist. She is a freelance writer, consultant, and speaker in the nutrition, fitness, and health industries. In addition, she is a spokesperson for the International Society of Sports Nutrition.

Statements and opinions expressed on this Web site are those of the authors and not necessarily those of the publishers or advertisers. The information provided on this Web site should not be construed as medical instruction. Consult appropriate health-care professionals before taking action based on this information.