Multivitamin Reviews, Side Effects & More

Multivitamin for women and men
The longest clinical trial investigation on multivitamins in relation to chronic disease found that taking a daily multivitamin reduced overall rates of cancer by 8%.14

What is a Multivitamin?

A vitamin is an organic compound that must be consumed through the diet to support essential biochemical processes within the body. Vitamins cannot be produced and synthesized within the body.1 In nature, vitamins are found in all living organisms – humans can consume vitamins from both plant and animal sources.

Multivitamins are a type of supplement that contain a concentrated form of multiple essential vitamins, and are one of the most widely used supplements. There are many different types of multivitamins, but in general, multivitamins are taken to ensure that the consumer is receiving adequate amounts of essential daily vitamins through their diet. Many multivitamins also include essential minerals (for example, iron). Since vitamin requirements vary based on body weight, age, gender, life stage, and more, there is no one multivitamin that will work for everyone; multivitamins can be categorized based on the group they are intended to be used by. For example, prenatal multivitamins are a type of multivitamin intended to address the nutrient needs of pregnant women. It is important to choose a multivitamin based upon your specific nutrient requirements.

Are Multivitamins good for you?

When taken in safe amounts, yes. Without enough vitamins, the body cannot function properly. Although most health organizations primarily recommend eating a healthy, nutrient-rich diet to receive enough vitamins, this is not always possible.

For example, a study in the United States separated participants into multivitamin users and multivitamin non-users. Among multivitamin non-users, only 72-74% had adequate vitamin intakes.4 However, among multivitamin users, 83-84% had adequate vitamin intakes.4 This study shows that for some subpopulations, taking daily vitamin pills can promote adequate nutrition.

Since vitamins are essential nutrients, they must be consumed through the diet. Humans cannot function without enough essential vitamins, since without these vitamins, key biological processes will not be able to function properly. Vitamins and minerals behave as cofactors in bodily reactions. Therefore, receiving insufficient amounts of vitamins from the diet will result in a vitamin deficiency, which is a serious health condition that can have many negative health effects if left untreated.1 Though vitamin deficiencies are currently uncommon in developed countries, they may occur in some populations.2 Taking a daily multivitamin can provide beneficial effects like helping prevent mild deficiencies, and improving vitamin intakes overall.4

Should I take a Multivitamin?

For general users, taking a daily multivitamin can help improve nutrient intakes.4

Additionally, there is plenty of evidence to suggest that certain populations with distinct vitamin requirements should take a multivitamin. According to the Dietary Guidelines for Americans, 2015-2020:3

Multivitamin use in the United States.
A 2003-2006 study from the US found that multivitamins are one of the most widely used dietary supplements.7
  • Pregnant women and women planning to become pregnant should consume extra iron and folic acid, since pregnant women require more iron and folic acid can prevent birth defects in pregnancy.
  • Adolescent girls 13-18, and women 19-50 have low rates of iron intake when compared to the Recommended Dietary Allowance (RDA), which puts them at risk for anemia. This is largely a result of women’s menstrual cycles. Women and young girls may benefit from consuming a multivitamin which includes iron.
  • Elderly adults over the age of 50 should consume more vitamin B12, vitamin D, and calcium, since vitamin D and calcium have been associated with reduced rates of osteoporosis and bone fractures in seniors, and seniors seem to be less able to absorb vitamin B12.5
  • Vegans and vegetarians may need to consume multivitamins containing vitamin B12, since vitamin B12 is not naturally found in plant-based foods.
  • Infants should receive a vitamin D supplement, either in multivitamin form or through fortified foods.6
  • In young children, intakes of iron, vitamin D, and other vitamins may be low, since children need specific amounts of vitamins to support normal growth and development.6
  • Certain chronic health conditions may increase nutrient requirements or impair absorption of certain vitamins (i.e. chronic pancreatitis); a doctor may recommend multivitamins to individuals with these conditions.

For these groups, multivitamins may be necessary to support overall health.

If you are part of an at-risk group and you feel a multivitamin may be beneficial to your health, consult with a doctor to determine which multivitamin is right for you.

Multivitamin Side Effects

If multivitamins are taken in very large quantities, adverse side effects are likely to result, and there is a high potential for toxicity when vitamins are consumed in large amounts. Fat-soluble vitamins such as vitamin D are particularly dangerous to consume in high quantities, since these can be stored in the body for longer periods of time than water-soluble vitamins. Some water-soluble vitamins, such as vitamin B12, are not associated with adverse effects, while others, like vitamin B6, may cause adverse effects.

When combined with a vitamin-rich diet, multivitamins can push vitamin intakes over the Upper Intake Level (UL). In the same study that showed multivitamin users had a higher prevalence of adequate vitamin intakes than non-users, multivitamin users were shown to be more at-risk for consuming excessive levels of vitamins. 10-15% of multivitamins users in the study had intakes of vitamin A, iron, and zinc over the UL, which could result in side effects.4

Adverse and toxic effects that could result from consuming excessive quantities of vitamins include:8, 9, 10

  • Headache
  • Stomach pain
  • Nausea
  • Vomiting
  • Heartburn
  • Numbness
  • Irritated skin (i.e. dermatitis, rash)
  • Sore eyes
  • Constipation
  • Liver damage
  • Kidney damage
  • Weight loss
  • Skin flushing
  • Irregular heartbeat

Multivitamin Ingredients

All of these vitamins are essential for human health. Most multivitamins contain a selection of these vitamins, depending on the type.

Even though vitamins and minerals are defined as two separate classes of compounds, some essential minerals necessary to support human health are often included in multivitamin supplements. Some minerals commonly found in multivitamins are:

If you are looking for a multivitamin containing a specific mineral – for example, a multivitamin with iron, or a multivitamin with calcium, check the label to see if it contains enough essential minerals to help you meet your nutrient requirements. Standalone mineral supplements are also available.

Multivitamin for Men

Thinking of buying a Men’s Multivitamin? Click here for the latest buying guide.

A multivitamin for men will be formulated differently than a women’s multivitamin. Generally, men require higher doses of vitamins than women in order to support their health. The higher doses required for men is mainly due to the difference in body size between men in women, since men tend to be larger than women, and men tend to have more muscle mass.12 In addition, different multivitamins are also created specifically for each age bracket in order to fulfill the changing vitamin requirements as men age.

Some multivitamins are created to address specific issues in men’s health. For example, some vitamins for men are intended to support active lifestyles and athletes. Multivitamins containing certain minerals, such as calcium, are intended to support bone and joint health as men age.

Multivitamin for Women

Thinking of buying a Women’s Multivitamin? Click here for the latest buying guide.

Vitamins for women are intended to address women’s nutrient requirements, since the Recommended Dietary Allowance (RDA) for each vitamin is different for women. Women usually need smaller amounts of vitamins than men, as they tend to be smaller in size and stature.12 Multivitamin formulas differ, depending on life stage and the age of the woman taking them. Vitamin requirements change as women get older, with some vitamins becoming less important, and others becoming more important.

Many vitamins are also formulated to address women’s specific health needs. Iron is a common ingredient in women’s multivitamins, since women and young girls often have low levels of iron.5 Others are intended to support varying life stages – for example, some multivitamins for women are intended to address the health needs of those going through menopause.

A prenatal multivitamin is aimed at supporting women who are planning to become pregnant, and women who are already pregnant. Many vitamin requirements increase when women are pregnant, as the developing fetus requires nutrients too. A prenatal vitamin, as well as any women’s multivitamin, almost certainly contains high levels of folic acid, which can prevent neural tube defects in babies. Since most neural tube defects occur in the first few weeks of pregnancy, when many women are unaware that they were pregnant, general women’s multivitamins usually contain folic acid as well, in the hopes that if a woman becomes pregnant while taking the multivitamin, the folic acid will prevent a neural tube defect occurring before she realizes she is pregnant.3

Some women’s multivitamins are specifically aimed at breastfeeding women, to support the health of breastfeeding mothers and their babies.

All pregnant and breastfeeding women should consult with their healthcare provider before taking prenatal vitamins or multivitamins.

Multivitamin usage in the US over 18 years
Multivitamin use in the United States has increased steadily over the past 18 years for both women and men.

GNC Vitamins – and Other Retailers

GNC offers numerous multivitamins for a variety of dietary and medical requirements. Popular GNC multivitamin products include: Animal Pak, Alive! Multivitamin, Rainbow Light Multivitamins, and GNC Multivitamins.

Multivitamins are also readily available online and at almost all of your local pharmacies, drug stores or supermarkets.


Multivitamins are sometimes believed to reduce the risk of disease, cancer, and other chronic health conditions when taken by the general population. However, there is conflicting evidence to support this belief. Some of the evidence published over the last 30 years shows there is no benefit for those who do not have special nutrient needs. One systematic review from 2006 found that there was no link between multivitamin usage and reduced rates of cancer and chronic conditions, concluding that “evidence is insufficient to prove the presence or absence of benefits from use of multivitamin and mineral supplements to prevent cancer and chronic disease”.13

However, some recent evidence shows a possible benefit in regards to cancer and chronic health conditions. In the longest clinical trial investigation on multivitamins in relation to chronic disease, which was published in 2012 and followed participants for a median of 11 years, found that taking a daily multivitamin reduced the risk of developing cancer by 8%.14 Another study from 2010 found that multivitamin usage seemed to reduce the risk of experiencing a heart attack.15

Multivitamins appear to be most promising in protecting against age-related macular degeneration and vision loss. One study found that consistent multivitamin usage significantly reduced the chance of developing age-related macular degeneration and other visual impairments.16

Vitamin Reviews

Click here for the most comprehensive multivitamin supplement reviews.


  1. Food and Agriculture Organization of the United Nations (2004). Vitamin and mineral requirements in human nutrition. Retrieved 10 August 2016.
  2. Duggan, S. N., Smyth, N. D., O’Sullivan, M., Feehan, S., Ridgway, P. F., & Conlon, K. C. (2014). The prevalence of malnutrition and fat-soluble vitamin deficiencies in chronic pancreatitis. Nutrition in Clinical Practice, 29 (3), 348-354.
  3. 2015–2020 Dietary Guidelines for Americans. 8th Edition. December 2015.
  4. Murphy, S. P., White, K. K., Park, S-Y., Sharma, S. (2007) Multivitamin-multimineral supplements’ effect on total nutrient intake. American Journal of Clinical Nutrition, 85 (1), 280S-284S.
  5. Chung, M., Balk, E. M., Brendel, M., Ip, S., Lau, J., Lee, J., et al. (2009). Vitamin D and calcium: a systematic review of health outcomes. Evidence Report/Technology Assessment No. 183 prepared by the Tufts Evidence-based Practice Center under Contract No. 290-2007-10055-I.
  6. Wagner, C. L., Greer, F. R., and the Section on Breastfeeding and Committee on Nutrition (2008). Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics, 122 (5), 1142-1152.
  7. Bailey, R. L., Gahche, J. J., Lentino, C. V., Dwyer, J. T., Engel, J. S., et al. (2011). Dietary supplement use in the United States, 2003-2006. Journal of Nutrition, 141 (2), 261-6.
  8. Hayman, R. M., & Dalziel, S. R. (2012). Acute vitamin A toxicity: A report of three paediatric cases. Journal of Paediatrics and Child Health, 48 (3), E98-E100.
  9. Kaur, P., Mishra, S. K., & Mithal, A. (2015). Vitamin D toxicity resulting from overzealous correction of vitamin D deficiency. Clinical Endocrinology, 83 (3), 327-331.
  10. Capuzzi DM, Morgan JM, Brusco OA, Intenzo CM (2000). Niacin dosing: relationship to benefits and adverse effects. Current Atherosclerosis Reports, 2 (1), 64–71.
  11. Institute of Medicine (2006). Dietary Reference Intakes: The essential guide to nutrient requirements. Washington (DC): The National Academies Press; 2006.
  12. Institute of Medicine. Food and Nutrition Board. (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press.
  13. Huang H. Y., Caballero, B., Chang, S., Alberg, A. J., Semba, R. D., Schneyer, C. R., et al. (2006). The efficacy and safety of multivitamin and mineral supplement use to prevent cancer and chronic disease in adults: a systematic review for a National Institutes of Health state-of-the-science conference. Annals of Internal Medicine, 145 (5), 372-85.
  14. Gaziano, J. M., Sesso, H. D., Christen, W. G., Bubes, V., Smith, J. P., MacFadyen, J., et al (2012). Multivitamins in the prevention of cancer in men: the Physicians’ Health Study II randomized controlled trial. Journal of the American Medical Association, 308 (18), 1871-80.
  15. Rautiainen, S., Åkesson, A., Levitan, E. B., Morgenstern, R., Mittleman, M. A., Wolk, A. (2010). Multivitamin use and the risk of myocardial infarction: a population-based cohort of Swedish women. American Journal of Clinical Nutrition, 92, 1251-1256.
  16. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. JAMA Ophthalmology, 119, 1417-1436.