Multivitamins are used by at least 33% of the U.S. population, so it makes the topic a wide reaching one [1]. However, although it is widespread in its appeal, how much do we really know about multivitamin supplementation? Are you aware of its effectiveness? Its possible negatives? Various considerations affecting its impact? Well, in this article, we will look into the research and determine the legitimacy and impact of multivitamin supplementation; however, we will not cover the adequate intake or go over  each specific vitamin.

What is a Multivitamin?

Although it may seem rather obvious what a multivitamin is, it always helps to have an attempt at a definition so we find ourselves on the same page. While the medical dictionaries would describe a multivitamin as “multiple vitamins” and while this is likely accurate enough, most studies examined for this article define a multivitamin by any supplement containing 3 or more vitamins – small difference, but it may matter [1].

Are Multivitamins effective?

While the answer to this question may seem obvious to you, it is a bit more complex than one would imagine if we investigate the question for our own edification. The simple answer is, “yes”; however, there are considerations to take into account.  


First off, bioavailability is defined as the absorption and utilization of a nutrient [2]. As a matter of fact, there is an article dedicated to this topic and the various influences to bioavailability of nutrients on this website, located here. There are factors that influence the bioavailability of vitamins and minerals from the nutrient being bound before absorption to a point that it can no longer be absorbed, making nutrients insoluble and therefor inabsorbable as they are indigestible, and competing nutrients for the same absorption system along the intestines [3]. We will discuss some of these factors in more detail later on. What we should be aware of, however, is that varying bioavailability of micronutrients can increase or decrease the effectiveness of a multivitamin.


Being deficient in a particular nutrient can also increase or decrease the effectiveness of a multivitamin as micronutrients are often dependent on one another for complete bioavailability. Deficiencies in a micronutrient typically manifest in the increased bioavailability of that micronutrient once the nutrient is available in the body [3].

Benefits of Multivitamins?

The benefits of multivitamin intake are high. Ingesting any vitamins on a consistent basis is a good situation (keeping dosage in check), and a multivitamin is a convenient way of going about hitting all the bases. Since the average American, before supplement use, intakes below the estimated average requirement (EAR), the use of a vitamin supplement is favorable; some have a daily intake of less than 8% of the recommended value, which will eventually lead to chronic health problems [4]. That being the case, a multivitamin has a strong appeal and has been proven to have a significant positive impact on vitamin levels in the body [1].

Specifically, multivitamins have been thought to increase cancer risk, but the reality is that it is not multivitamins that increase cancer risk on their own. If a person is deficient in a series of vitamins and the multivitamin fulfills that need, then the risk is not increased [1]. The risk of certain cancer is actually reduced from having a good vitamin profile [5][6][9].

Certain vitamins are simply absorbed better if they come from a supplement form over that found in micronutrient dense foods, so in these cases, multivitamins are also a benefit [3][7][10].

Problems of Multivitamins?

We just finished talking about how cancer is not a risk with vitamins and while that is true for the most part, there is some legitimacy to it. An overconsumption of vitamins has shown a slight increase in cancer risk, depending on the vitamin [5]. So, if you eat a balanced diet dense with micronutrients and then supplement further with high doses of vitamins and minerals, then yes, the risk is increased.

Now, although multivitamins do an admirable job of covering one’s tracks in terms of deficiency, there are still certain vitamins that tend to be left in a deficient state in the body regardless of supplementation with a single dose of multivitamin [8] These deficiencies are dependent on the population and change from vitamin to vitamin and may need extra supplementation in that particular vitamin.

Going back to the concept of bioavailability, there is also proof that for certain vitamin interactions, it would be better to separate certain vitamins rather than taking them in one go as done with a multivitamin [3]. An example of this is non-haem iron and calcium as if they are taken together, calcium can block the absorption of the iron through the intestinal wall, which could lead to iron deficiency [3]. So, for an undetermined percentage of a benefit, it might be better to separate vitamin intake as some associations can be detrimental to bioavailability of particular micronutrients.

On a side note, although there needs to be much more science on the subject, multivitamins may not offer the benefits of phytochemicals, either.

Optimizing Multivitamin Intake?

This should be simple enough; take a multivitamin that is set up for your current condition. This means that if you are a 14 years old girl, take a multivitamin set up for adolescence, not one for a 55 year old man – simple, right? Also, be sure you are aware that a multivitamin helps, but it should not take the entire load, and as such, eating a balanced diet would help tremendously. Also, being aware of certain vitamin interactions might be helpful get the most out of your vitamin supplement. Finally, consume with food as the slowing of the digestion will lead to a lower probability you will experience stomach discomfort.

Who should be taking a Multivitamin?

Anyone and everyone that is deficient in a series of multivitamins. Basically, if you are not consuming the recommended levels of fruits and vegetables, especially, then it may be wise to supplement with a multivitamin. If you have a relatively healthy, balanced nutrition, then it is probably alright to also cover your bases with a multivitamin (or half a multivitamin). On the other hand, if you consume large quantities of micronutrient dense foods on a regular basis, your need for a multivitamin supplement is unnecessary.

That covers the general population, but what of the people on either end? If you are younger, you likely do not have the nutrition thing bolted down and should go ahead and take the appropriate multivitamin for your age, sex, and activity level – the same is true for elderly individuals. Do not take the wrong multivitamin as this will have detrimental effects on your health.


To wrap this up, it seems evident that multivitamins have their use and are absolutely useful for covering deficiencies in one’s nutrition if nutrition is not your forte. However, some vitamin deficiencies are not adequately attenuated by multivitamin supplementation alone. Not only that, over supplementation with multivitamins also have detrimental health effects (increased risk of cancer, for example). While the bioavailability (absorption and use by the body) of multivitamins is often less than optimal, the likelihood this will have a real world impact is low. Finally, it would be recommended that if a person decides to supplement with a multivitamin, they should purchase a multivitamin that fits their physiological condition (buying kid multivitamins for kids, women multivitamin for women, multivitamin for those over 50 if you are over 50, etc – common sense) otherwise long term use of an inappropriate multivitamin can have detrimental effects to health.

Writer: Nicolas Verhoeven
This is educational material only and not meant to be prescripton, consult your physician before making any changes.


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[2] Krebs, N. F. (2001). Bioavailability of Dietary Supplements and Impact of Physiologic State: Infants, Children and Adolescents. American Society of Nutritional Sciences, 131(4), 1351-1354. Retrieved from

[3] Nutrient bioavailability - getting the most out of food (EUFIC). (n.d.). Retrieved from

[4] Fulgoni, V. L., Keast, D. R., Bailey, R. L., & Dwyer, J. (2011). Foods, Fortificants, and Supplements: Where Do Americans Get Their Nutrients? Journal of Nutrition, 141(10), 1847-1854. Retrieved from

[5] Vitamins do not cause cancer! | Linus Pauling Institute | Oregon State University. (n.d.). Retrieved from

[6] JAMA | Multivitamins in the Prevention of Cancer in MenThe Physicians' Health Study II Randomized Controlled TrialMultivitamins in the Prevention of Cancer in Men. (n.d.). Retrieved from

[7] Hannon-Fletcher, M. P. (2004). Determining bioavailability of food folates in a controlled intervention study. American Journal of Clinical Nutrition, 80(4), 911-918. Retrieved from

[8] Bailey, R. L., Fulgoni, V. L., Keast, D. R., Lentino, C. V., & Dwyer, J. T. (2012). Do Dietary Supplements Improve Micronutrient Sufficiency in Children and Adolescents? The Journal of Pediatrics, 161(5), 837-842.e3. Retrieved from

[9] Greenwald, P. (2007). Clinical trials of vitamin and mineral supplements for cancer prevention.American Journal of Clinical Nutrition, 85(1), 314-317. Retrieved from

[10] Supplemental Forms | Linus Pauling Institute | Oregon State University. (n.d.). Retrieved from

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