There are two main ways to use vitamins and mineral supplements: "megadose" and nutritional therapy. 

The megadose approach involves taking supplements at doses far above nutritional needs in hopes of producing a specific medical benefit. This technique essentially uses nutrients as natural drugs. The individual supplement articles in this encyclopedia explain what is known about the potential risks and benefits of megadose therapy. 

This article addresses the second approach: taking nutrients at the level of nutritional needs. We discuss general issues regarding such "nutritional insurance" and indicate which nutrients you should consider taking on a daily basis.


There is no doubt that it's important to get enough of all necessary nutrients. However, the process of determining proper daily intake levels for vitamins and minerals is far from an exact science and the recommendations issued by experts in various countries often disagree to a certain extent.

In general, while it is fairly easy to determine the minimum nutrient intakes that are necessary to avoid frank malnutrition, there's no straightforward way to determine optimum intake levels. Furthermore, individual needs undoubtedly vary based on numerous factors, including age, genetics, lifestyle, other foods in the diet, and many additional environmental influences; no schedule of official recommendations could possibly take all these factors into account, even if all the necessary data existed (which it doesn't).

Thus, all recommendations for daily nutrient intake must be regarded as approximate. The individual supplement articles in this encyclopedia summarize the current US recommendations.

Common Nutritional Deficiencies

Severe deficiencies of vitamins or minerals are rare in the developed world. However, evidence suggests that slight deficiencies in certain nutrients may be relatively common. These include calcium , 15,16chromium , 14folate , 13magnesium , 17 vitamin B 6 , 18-20vitamin C , 21-24 vitamin B 12 (primarily in the elderly), 25-28vitamin D , 33vitamin E , 40-42 and zinc . 16,34-37

While few people are so deficient in these nutrients to show symptoms of outright malnutrition, subtle deficiencies may increase the risk of a number of diseases. For example, insufficient intake of calcium and vitamin D may increase your chances of developing osteoporosis, and inadequate folate and vitamin B 6 may speed the development of heart disease.

Thus, taking supplements to supply these important vitamins and minerals as a form of insurance may be a good idea. For standard dosage recommendations as well as safety issues, follow the links above to the full articles.

Besides vitamins and minerals, intake of essential fatty acids may be commonly inadequate. For more information, see the articles on omega-6 and omega-3 fatty acids.

Women may develop iron deficiency, but men hardly ever do. Even in women, iron supplements are not beneficial in the absence of true deficiency. We recommend avoiding iron supplements unless tests show that you really need them.

Multivitamin/Mineral Supplements

The simplest way to support your nutrition is to take a general multivitamin and mineral supplement providing a broad range of nutrients at standard nutritional levels. However, there are a few caveats to keep in mind.

  • Some supplements include very high doses of certain nutrients, such as antioxidants. As described above, when you take nutrients in this fashion, you are using them as drugs rather than nutrients; you are no longer in the world of nutritional supplementation and have passed into the riskier world of megadose treatment.
  • We recommend that you use an iron-free multivitamin and mineral supplement unless you have been tested and found to be deficient in iron.
  • The minerals calcium and magnesium are very bulky, and few multivitamin/mineral supplements provide the daily requirement. These minerals generally must be taken in the form of additional pills. Note: It isn't possible for your body to absorb a day's worth of calcium in a single dose. At least two doses are necessary.
  • Finally, note that food may contain many nonessential substances, such as carotenoids and bioflavonoids, that nonetheless enhance health. For this reason, no nutrient supplement should be regarded as a substitute for a healthy and varied diet.
  • Taking Individual Supplements

    One problem with multivitamin/mineral supplements is that some nutrients may interfere with the absorption of others. For this reason, there may be advantages to taking supplements separately. (The hassle factor is a strong disadvantage!) In addition, this method allows one to avoid taking vitamins and minerals one doesn't need.

    If you do use this approach, keep in mind the following: 

  • Minerals come in many different chemical forms, technically called "salts." For example, you can purchase calcium as calcium carbonate, calcium citrate, calcium orotate, and in half a dozen or more other forms. In some cases, certain salts of minerals are known to be better absorbed than others. This is particularly the case with calcium , as described in the full article.
  • When you take zinc , you should balance it with copper .
  • There may be advantages to taking certain nutrients at levels a bit higher than the standard recommendations, but each nutrient presents its own issues. More is not necessarily better. See each individual nutrient article for details.
  • Natural vs. Synthetic Vitamins

    Many people wonder whether "natural" vitamins are better than "synthetic" ones. This question, however, is a bit of a red herring. Ultimately, no vitamin or mineral supplement is "natural." Purified vitamins and minerals are refined, processed products analogous to white sugar or artificial fertilizer. It doesn't much matter whether they are extracted from foods or manufactured in a laboratory: the result is the same. For example, vitamin C made from rose hips is chemically identical to vitamin C synthesized from scratch. Both are ascorbic acid.

    Rose hips themselves, however, supply many nutrients along with vitamin C. If you truly wish to get your vitamins naturally, you might consider taking them as freeze-dried or condensed whole food supplements rather than as purified vitamins. This might offer a specific advantage over purified vitamins: as we noted above, fruits and vegetables may provide substances that are not actually essential but that promote better health.

    Therapeutic Uses

    Under certain conditions, the need for many nutrients may increase. These include illnesses such as diabetes , Crohn's disease , HIV , and ulcerative colitis . Furthermore, individuals who smoke cigarettes or overuse alcohol may need additional nutrients. Follow the links to the individual articles for more information.

    Medications may increase the need for certain nutrients; if you look up your own medications in the Drug Interaction section of this encyclopedia, you will find what is known about these so-called nutrient depletions.

    Other potential uses of multivitamins generally lack strong support.

    Some but not all evidence hints that multivitamin/multimineral supplements may help prevent infections in seniors or otherwise enhance immunity. 7, 8, 9, 32,38,39,43,57,63-64 However, there are strong suspicions that scientific fraud may have tainted this research, and when the potentially fraudulent studies are disregarded the evidence looks more negative than positive. 70

    Similarly, some but not all studies suggest that multivitamin/multimineral supplements can enhance mental function , and here, too, there are concerns about potential fraud. 11,12,48-51,58,59, 62,71,74 In general, the best designed studies have failed to find benefit. However, it is quite possible that multivitamin/multimineral supplements are helpful for people with marked vitamin or mineral malnutrition. 71

    One study found that use of a multivitamin tablet improved mood, but not cognitive function, in hospitalized acutely ill seniors. 72 Another study failed to find that a mix of multivitamin (either general, or consisting of B-complex vitamins) were more effective than placebo for treating depression in healthy young adults. 75

    Incomplete, and in some cases contradictory, evidence suggests that use of multivitamin and/or multimineral supplements might reduce antisocial behavior in children and young adults (especially those who are malnourished), 40,47,52 prevent bedsores, 54 lower blood pressure , 53 improve fertility in women , 10 improve general well-being , 47,51, 65enhance sports performance , 67 enhance growth in children, 56 speed healing of minor wounds,55 reduce the pain of osteoarthritis , 46 reduce pregnancy-related nausea (“morning sickness”), 47decrease risk of numerous birth defects , 68 help control menopausal hot flashes , 69 decrease symptoms of premenstrual stress syndrome (PMS)1-4 and ordinary stress , 5,6reduce risk of prostate cancer , 66 and help prevent cataracts . 76

    In a double-blind study of 40 people undergoing radiation therapy for breast cancer, use of a standard multivitamin preparation failed to reduce fatigue as compared to placebo. 73 (In fact, people in the placebo group may have done somewhat better than those given the vitamin.)

    Safety Issues

    Standard multivitamin/multimineral tablets contain nutrients at levels believed to be safe for the majority of healthy people, as indicated by amounts at or below the recommended daily allowance. However, even these supplements could be harmful for people with certain diseases, such as kidney or liver disease, or for people taking certain medications, such as warfarin .

    There are other multivitamin/multimineral tablets that contain high levels of certain nutrients far above nutritional needs. These could conceivably present risks for healthy people, particularly if they are taken in combination with additional specific supplements. Almost any mineral can be toxic if taken to excess, and there are also risks with excessive intake of vitamins A, B 6 , and D.

    One study found that use of multivitamin/mineral supplements may actually increase the infectivity of women with HIV. 61 The reasons for this are unclear.