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,17vitamin B6,18-20vitamin C,21-24vitamin B12 (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 pressure ulcers (bed sores),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.)

There may be a link between maternal mulitvitamin use during pregnancy and a slight reduction in risk for a child with autism spectrum disorder with an intellectual disability. A population-based study evaluated 273,107 children who were 4-15 years old. Multivitamins, and iron and folic acid supplements were started after the first prenatal visit.77

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.



1. London RS, Bradley L, Chiamori NY. Effect of a nutritional supplement on premenstrual symptomatology in women with premenstrual syndrome: a double-blind longitudinal study. J Am Coll Nutr. 1991;10:494-499.

2. Reynolds MA, London RS. Efficacy of a multivitamin/mineral supplement in the treatment of the premenstrual syndrome [abstract]. J Am Coll Nutr. 1988;7:416.

3. Stewart A. Clinical and biochemical effects of nutritional supplementation on the premenstrual syndrome. J Reprod Med. 1987;32:435-441.

4. Chakmakjian ZH, Higgins CE, Abraham GE. The effect of a nutritional supplement, OptiviteŴ for women, on premenstrual tension syndromes: II. Effect on symptomatology, using a double-blind, cross-over design. J Appl Nutr. 1985;37:12-17.

5. Schlebusch L, Bosch BA, Polglase G, et al. A double-blind, placebo-controlled, double-centre study of the effects of an oral multivitamin-mineral combination on stress. S Afr Med J. 2000;90:1216-1223.

6. Carroll D, Ring C, Suter M, et al. The effects of an oral multivitamin combination with calcium, magnesium, and zinc on psychological well-being in healthy young male volunteers: a double-blind placebo-controlled trial. Psychopharmacology (Berl). 2000;150:220-225.

7. Girodon F, Galan P, Monget AL, et al. Impact of trace elements and vitamin supplementation on immunity and infections in institutionalized elderly patients: a randomized controlled trial. MIN. VIT. AOX. geriatric network. Arch Intern Med. 1999;159:748-754.

8. Chandra RK, Puri S. Nutritional support improves antibody response to influenza virus vaccine in the elderly. Br Med J (Clin Res Ed). 1985;291:705-706.

9. Ender PT, DeRussy PK, Caldwell MM, et al. The effect of a multivitamin on the immunologic response to the influenza vaccine in the elderly. Infect Dis Clin Pract. 2001;10:81-85.

10. Czeizel AE, Metneki J, Dudas I. The effect of preconceptional multivitamin supplementation on fertility. Int J Vitam Nutr Res. 1996;66:55-58.

11. Benton D. Micro-nutrient supplementation and the intelligence of children. Neurosci Biobehav Rev. 2001;25:297-309

12. Chandra RK. Effect of vitamin and trace-element supplementation on cognitive function in elderly subjects. Nutrition. 2001;17:709-712.

13. Wald NJ, et al. Quantifying the effect of folic acid. Lancet. 2001;15;358:2069-2073.

14. Mertz W. Chromium in human nutrition: a review. J Nutr. 1993;123:626-633.

15. McCarron DA. Dietary calcium and lower blood pressure: we can all benefit [editorial]. JAMA. 1996;275:1128-1129.

16. Ervin RB, Kennedy-Stephenson J. Mineral intakes of elderly adult supplement and non-supplement users in the third national health and nutrition examination survey. J Nutr. 2002;132:3422-3427.

17. Alaimo K, McDowell MA, Briefel RR, et al. Dietary intake of vitamins, minerals and fiber of persons age 2 months and over in the United States: Third National Health and Nutrition Examination Survey, phase 1, 1988-91. Advance Data from Vital and Health Statistics. 1994;258:1-26.

18. Kant AK, Block G. Dietary vitamin B-6 intake and food sources in the US population: NHANES II, 1976-1980. Am J Clin Nutr. 1990;52:707-716.

19. van der Wielen RP, de Groot LC, van Staveren WA. Dietary intake of water soluble vitamins in elderly people living in a Western society (1980-1993). Nutr Res. 1994;14:605-638.

20. Albertson AM, Toblemann RC, Engstrom A, et al. Nutrient intakes of 2- to 10-year-old American children: 10-year trends. J Am Diet Assoc. 1992;92:1492-1496.

21. Hercberg S, Preziosi P, Galan P, et al. Vitamin status of a healthy French population: dietary intakes and biochemical markers. Int J Vitam Nutr Res. 1994;64:220-232.

22. Lowik MR, Wedel M, Kistemaker C, et al. Assessment of the adequacy of vitamin C intake in the Netherlands [abstract]. J Am Coll Nutr. 1991;10:544.

23. Baker B. Vitamin C deficiency common in hospitalized. Fam Pract News. 1995 March:25.

24. Taylor CA, Hampl JS, Johnston CS. Low intakes of vegetables and fruits, especially citrus fruits, lead to inadequate vitamin C intakes among adults. Eur J Clin Nutr. 2000;54:573-578.

25. Saltzman JR, Kemp JA, Golner BB, et al. Effect of hypochlorhydria due to omeprazole treatment or atrophic gastritis on protein-bound vitamin B12 absorption. J Am Coll Nutr. 1994;13:584-591.

26. van Goor L, Woiski MD, Lagaay AM, et al. Review: cobalamin deficiency and mental impairment in elderly people. Age Ageing. 1995;24:536-542.

27. Pennypacker LC, Allen RH, Kelly JP, et al. High prevalence of cobalamin deficiency in elderly outpatients. J Am Geriatr Soc. 1992;40:1197-1204.

28. Yao Y, Yao SL, Yao SS, et al. Prevalence of vitamin B 12 deficiency among geriatric outpatients. J Fam Pract. 1992;35:524-528.

29. Barringer TA, Kirk JK, Santaniello AC, et al. Effect of a multivitamin and mineral supplement on infection and quality of life. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. 2003;138:365-371.

30. Bogden JD, Bendich A, Kemp FW, et al. Daily micronutrient supplements enhance delayed-hypersensitivity skin test responses in older people. Am J Clin Nutr. 1994;60:437-447.

31. Berger MM, Spertini F, Shenkin A, et al. Trace element supplementation modulates pulmonary infection rates after major burns: a double-blind, placebo-controlled trial. Am J Clin Nutr. 1998;68:365-371.

32. Graat JM, Schouten EG, Kok FJ. Effect of daily vitamin E and multivitamin-mineral supplementation on acute respiratory tract infections in elderly persons: a randomized controlled trial. JAMA. 2002;288:715-721.

33. Utiger RD. The need for more vitamin D. N Engl J Med. 1998;338:828-829.

34. Sandstead HH. Zinc nutrition in the United States. Am J Clin Nutr. 1973;26:1251-1260.

35. Prasad AS. Zinc deficiency in women, infants, and children. J Am Coll Nutr. 1996;15:113-120.

36. Goldenberg RL, Tamura T, Neggers Y, et al. The effect of zinc supplementation on pregnancy outcome. JAMA. 1995;274:463-468.

37. Stang J, Story MT, Harnack L, et al. Relationships between vitamin and mineral supplement use, dietary intake, and dietary adequacy among adolescents. J Am Diet Assoc. 2000;100:905-910.

38. Girodon F, Lombard M, Galan P, et al. Effect of micronutrient supplementation on infection in institutionalized elderly subjects: a controlled trial. Ann Nutr Metab. 1997;41:98-107.

39. Chandra RK. Effect of vitamin and trace-element supplementation on immune responses and infection in elderly subjects. Lancet. 1992;340:1124-1127.

40. Schoenthaler SJ, Amos S, Doraz W, et al. The effect of randomized vitamin-mineral supplementation on violent and non-violent antisocial behavior among incarcerated juveniles. J Nutr Environ Med. 1977;7:343-352.

41. Murphy SP, Subar AF, Block G. Vitamin E intakes and sources in the United States. Am J Clin Nutr. 1990;52:361-367.

42. Ford ES, Sowell A. Serum alpha-tocopherol status in the United States population: findings from the Third National Health and Nutrition Examination study. Am J Epidemiol. 1999;150:290-300.

43. Jain AL. Influence of vitamins and trace-elements on the incidence of respiratory infection in the elderly. Nutr Res. 2002;22:85-87.

44. Czeizel AE, Dudas I, Fritz G, et al. The effect of periconceptional multivitamin-mineral supplementation on vertigo, nausea and vomiting in the first trimester of pregnancy. Arch Gynecol Obstet. 1992;251:181-185

45. Ussher JM, Dewberry C, Malson H, et al. The relationship between health related quality of life and dietary supplementation in British middle managers: a double blind placebo controlled study. Psychol Health. 1995;10:97-111.

46. Colker CM, Swain M, Lynch L, et al. Effects of a milk-based bioactive micronutrient beverage on pain symptoms and activity of adults with osteoarthritis: a double-blind, placebo-controlled clinical evaluation. Nutrition. 2002;18:388-392.

47. Schoenthaler SJ, Bier ID. The effect of vitamin-mineral supplementation on juvenile delinquency among American schoolchildren: a randomized, double-blind placebo-controlled trial. J Altern Complement Med. 2000;6:7-17.

48. Schoenthaler SJ, Amos SP, Doraz WE, et al. Controlled trial of vitamin-mineral supplementation on intelligence and brain function. Pers Individual Differences. 1991;12:343-350.

49. Schoenthaler SJ, Amos SP, Eysenck HJ, et al. Controlled trial of vitamin-mineral supplementation: effects on intelligence and performance. Pers Individual Differences. 1991;12:351-362.

50. Schoenthaler SJ, Bier ID. Vitamin-mineral intake and intelligence: a macrolevel analysis of randomized controlled trials. J Altern Complement Med. 1999;5:125-134.

51. Benton D, Fordy J, Haller J. The impact of long-term vitamin supplementation on cognitive functioning. Psychopharmacology. 1995;117:298-305.

52. Gesch CB, Hammond SM, Hampson SE, et al. Influence of supplementary vitamins, minerals and essential fatty acids on the antisocial behaviour of young adult prisoners. Randomised, placebo-controlled trial. Br J Psychiatry. 2002;181:22-28.

53. Farvid MS, Jalali M, Siassi F, et al. The impact of vitamins and/or mineral supplementation on blood pressure in type 2 diabetes. J Am Coll Nutr. 2004;23:272-279.

54. Houwing RH, Rozendaal M, Wouters-Wesseling W, et al. A randomised, double-blind assessment of the effect of nutritional supplementation on the prevention of pressure ulcers in hip-fracture patients. Clin Nutr. 2003;22:401-405.

55. Brown SA, Coimbra M, Coberly DM, et al. Oral nutritional supplementation accelerates skin wound healing: a randomized, placebo-controlled, double-arm, crossover study. Plast Reconstr Surg. 2004;114:237-244.

56. Ramakrishnan U, Aburto N, McCabe G, et al. Multimicronutrient interventions but not vitamin a or iron interventions alone improve child growth: results of 3 meta-analyses. J Nutr. 2004;134:2592-602.

57. Langkamp-Henken B, Bender BS, Gardner EM, et al. Nutritional formula enhanced immune function and reduced days of symptoms of upper respiratory tract infection in seniors. J Am Geriatr Soc. 2004;52:3-12.

58. Meguid MM, Shenkin A. Introduction: nutritional supplements and the quest to improve human performance—the need for the strictest standards and rigor when reporting clinical trials. Nutrition. 2003;19:955-956.

59. Smith R. Validity of Canadian studies: response of editor of BMJ. 2004;328:465.

60. Allsup SJ, Shenkin A, Gosney MA, et al. Can a short period of micronutrient supplementation in older institutionalized people improve response to influenza vaccine? A randomized, controlled trial. J Am Geriatr Soc. 2004;52:20-24.

61. McClelland RS, Baeten JM, Overbaugh J, et al. Micronutrient supplementation increases genital tract shedding of HIV-1 in women: results of a randomized trial. J Acquir Immune Defic Syndr. 2004;37:1657-1663.

62. Wolters M, Hickstein M, Flintermann A, et al. Cognitive performance in relation to vitamin status in healthy elderly German women-the effect of 6-month multivitamin supplementation. Prev Med. 2005;41:253-259.

63. Avenell A, Campbell MK, Cook JA, et al. Effect of multivitamin and multimineral supplements on morbidity from infections in older people (MAVIS trial): pragmatic, randomised, double blind, placebo controlled trial. BMJ. 2005;331:324-329.

64. El-Kadiki A, Sutton AJ. Role of multivitamins and mineral supplements in preventing infections in elderly people: systematic review and meta-analysis of randomised controlled trials. BMJ. 2005 Mar 31. [Epub ahead of print]

65. Benton D, Haller J, Fordy J, et al. Vitamin supplementation for 1 year improves mood. Neuropsychobiology. 1995;32:98-105.

66. Meyer F, Galan P, Douville P, et al. Antioxidant vitamin and mineral supplementation and prostate cancer prevention in the SU.VI.MAX trial. Int J Cancer. 2005 Mar 30. [Epub ahead of print]

67. Fry AC, Bloomer RJ, Falvo MJ, et al. Effect of a liquid multivitamin/mineral supplement on anaerobic exercise performance. Res Sports Med. 2006;14:53-64.

68. Goh YI, Bollano E, Einarson TR, et al. Prenatal multivitamin supplementation and rates of congenital anomalies: a meta-analysis. J Obstet Gynaecol Can. 2006;28:680-689.

69. Kirby RS. Menopacenutrient therapy: an alternative approach to pharmaceutical treatments for menopause. Int J Fertil Womens Med. 2006;51:125-129.

70. Sternberg S, Roberts S. Nutritional supplements and infection in the elderly: Why do the findings conflict? Nutr J. 2006 Nov 23. [Epub ahead of print]

71. McNeill G, Avenell A, Campbell MK, et al. Effect of multivitamin and multimineral supplementation on cognitive function in men and women aged 65 years and over: a randomised controlled trial. Nutr J. 2007 May 2. [Epub ahead of print]

72. Gariballa S, Forster S. Effects of dietary supplements on depressive symptoms in older patients: A randomised double-blind placebo-controlled trial. Clin Nutr. 2007 Jul 25. [Epub ahead of print]

73. de Souza Fede AB, Bensi CG, Trufelli DC, et al. Multivitamins do not improve radiation therapy-related fatigue: results of a double-blind randomized crossover trial. Am J Clin Oncol. 2007;30:432-436.

74. The NEMO Study Group. Effect of a 12-mo micronutrient intervention on learning and memory in well-nourished and marginally nourished school-aged children: 2 parallel, randomized, placebo-controlled studies in Australia and Indonesia. Am J Clin Nutr. 2007;86:1082-1093.

75. America A, Milling LS. The efficacy of vitamins for reducing or preventing depression symptoms in healthy individuals: natural remedy or placebo? J Behav Med. 2007 Nov 13. [Epub ahead of print]

76. A randomized, double-masked, placebo-controlled clinical trial of multivitamin supplementation for age-related lens opacities clinical trial of nutritional supplements and age-related cataract report no. 3. Ophthalmology. 2008;115:599-607.e1.

77. DeVilbiss EA, Magnusson C, Gardner RM, et al. Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort: population based cohort study. BMJ. 2017;359:j4273.

Last reviewed December 2015 by EBSCO CAM Review Board  Last Updated: 3/12/2018