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Multivitamin supplements: yay or nay?

Updated: Apr 18, 2020

By Wageningen Beasts

We are living in the time of the fit girls and the fit guys. Healthy aging, superfoods, and Green happiness. These words determine the trend we live in now. People are looking for ways to stay healthy and young. Everyone has probably heard of multivitamin supplements, and they are marketed as healthy and essential for development. It is general belief that these multivitamins are good, which is why a lot of people are using them. In the Dutch population, about 50% of the females and 33% of the men are using supplements, yet not even 20% of the people meets a fruit and vegetable intake according to the recommended daily intake[1]. Can a multivitamin supplement replace fruits and vegetables? Or should it only be used as an addition to your diet to improve health? Do they even work? And can they be harmful?

What are vitamins?        Vitamins are (biochemical) compounds that are present in the body, as well as in food from which they can be derived. The body is an amazingly complex structure in which billions of reactions are taking place at this very moment. Think of things like metabolism, growth, immunity, DNA replication, and so much more. Vitamins play an important role in these processes. They are often involved in one or multiple different reactions (as a substrate or an enzyme). All in all, vitamins help the body to function[2].

Vitamins can either be hydrophilic (hydro=water, philos=loving; water-loving) or hydrophobic (hydro=water, phobos=fear; water-fearing). If you are not familiar with these terms, think of when you put oil and water in one glass as an example: the liquids will be separated, with the oil on top since it has a lower density than water. Thus, there are water-soluble vitamins and fat-soluble vitamins. Water-soluble vitamins include vitamins B and C, and fat-soluble vitamins include vitamins A, D, E, and K. One important difference between water- and fat-soluble vitamins is the foods they are present in. Fat-soluble vitamins are mainly present in food products that contain a lot of fat or oil, such as animal products (but also some vegetables, nuts, and seeds). Water-soluble vitamins are mainly present in foods that contain water (many foods such as fruits, vegetables, nuts, seeds, etcetera). A second important difference, is the way that these two types of vitamins are absorbed, transported, stored, and excreted. Mainly the latter two are of vital importance. Fat-soluble vitamins can be stored in body fat (in biological terms: adipose tissue), but water-soluble vitamins cannot be stored in the body. This means that excesses of water-soluble vitamins are excreted via the kidneys. In other words: when you ingest too much water-soluble vitamins, you will piss them out. Excesses of fat-soluble vitamins are stored in the adipose tissue of the body, which will in turn be used when the body needs these vitamins. This also means that when you ingest too much fat-soluble vitamins, the body cannot get rid of them[2]. Keep on reading to find out what the consequences are of this!

What are minerals?        Minerals, just like vitamins, are involved in many processes of the body. In that respect, they are quite similar to vitamins. There are just some differences in the processes they are involved in. The main difference is the classification: minerals are simple atoms, while vitamins are more complex molecules. As minerals are soluble in water, they can be excreted through the urine, just like water-soluble vitamins[2]. Vitamins and minerals together are classified as micronutrients.

Do you need micronutrients?    Surprise, surprise. Yes, you do! Vitamins and minerals are essential for vital functioning of the body. There are quite some diseases related to vitamin deficiencies (deficiency=shortage), such as scurvy from a vitamin C deficiency, rickets from a vitamin D deficiency, night blindness from vitamin A deficiencies, a lower bone mass from calcium deficiencies, and so on[2].

Luckily, these severe vitamin deficiencies are rare in the Western world, as the average diet contains enough vitamins and minerals to prevent these diseases from occurring. However, smaller, less severe, but not less relevant deficiencies occur frequently[3-5]. This could be caused by unbalanced diets that lack certain food categories (like vegetables, fruits, dairy, etcetera), examples of such diets can be vegetarian or vegan diets. Another cause is a lack of sunlight exposure. Such ‘small deficiencies’ will not result in disease, but they can result in some small (unnoticeable) side-effects, as well as suboptimal growth, recovery, etcetera. Having optimal intakes of vitamins and minerals thus could contribute to a good overall health.

What is the optimal dose of vitamins and minerals?      In the past, there has been much evidence that certain vitamins can decrease the risk of getting specific types of cancer. This lead to the conduction of several randomized controlled trials[6-8]: studies during which one group of participants was given the vitamin supplement (the intervention group), and the other group served as a control, to compare in which group the most cancers would occur. The hypothesis was that there would be less cancer cases in the intervention group than in the control group. Several months or years later, results were in. It appeared that there were more cancers in the intervention group than in the control group. This means that the vitamin increased cancer risk instead of decreasing it. The researchers assumed that the vitamin would be good, since previous research indicated that.

These researchers made a big mistake, but it is not different from the reasoning people have in daily life. Namely if something is proven to be healthy, then more of it would probably be even healthier. However, this is not how vitamins (and actually all nutrients) work. Taking too much of anything can be toxic, but taking too little is also bad for your health. Thus, it depends on the amount (or the dose) whether something is healthy or unhealthy. This is nicely illustrated in the figure here (Figure 1).

Figure 1. The U-curve of vitamin and mineral intakes and disease

This figure is called a U-curve, with on the y-axis (vertical axis) the occurrence of disease (you can read it as healthy at y=0 and unhealthy at y=100), and on the x-axis (horizontal axis) the dose of intake of the vitamin (0 on the left means a dose of 0, the more to the right means a higher dose). On the left of the x-axis, there will be a lot of disease: very low intake (deficiency) causes disease. On the right side of the x-axis, there will be a lot of disease as well: too high intakes are toxic. In the middle there is the perfect intake: within these lower and upper boundaries (the safe or healthy margin), there will be no disease. As was discussed before, the body can get rid of water-soluble vitamins and minerals via the urine, but not of fat-soluble vitamins, as these are stored in the body fat. This explains why mainly fat-soluble vitamins can have toxic effects when consumed in high dosages, whereas water-soluble vitamins and minerals will not be as toxic but also result in some side effects. Such side effects differ per micronutrient, but the main message is that these side effects are not as severe or toxic as those of fat-soluble vitamins. Thus, the middle of the U-curve shows the safe or optimal intake which is most healthy. More or less is unhealthy! So, can vitamins and minerals cure diseases like aids or cancer (which is claimed sometimes)? No. When you are deficient in a certain vitamin it can cause a particular disease (in extreme cases, such as scurvy from a vitamin C deficiency), and increasing the intake of that vitamin can cure this particular disease again. However, taking 1 gram of vitamin C per day will not cure any other diseases. It will also not contribute to better health than regular doses.

Therefore, when we look back at the example given above, about the studies that showed that certain vitamins cause cancer, this makes sense. Figure 2 below illustrates a potential U-curve for one of the vitamins that showed this effect in such a study: folate[9,10].

Figure 2. Potential U-curve for folic acid intake and cancer risk.

As you can see, low intakes can increase cancer risk. Increasing intake can decrease cancer risk, but further increases increase risk again. There are many examples of vitamins that show such a curve. In conclusion: too high dosages of vitamins are toxic!

What should the intake of each vitamin and mineral be?             The optimal intake differs per person, due to differences in age, gender, body composition, and genetics. Health institutes have come up with RDIs (Recommended Daily Intake, ADH (Aanbevolen Dagelijkse Hoeveelheden) in Dutch), which is a recommended level of intake, for each vitamin and mineral. The levels of the RDIs are high enough so that most of the population meets the individual optimal intake, while these are still within the safe limits of intake. Thus, consuming 100% of the RDIs of vitamins and minerals will make sure you have an optimal intake. Consuming more than the RDI will not lead to additional health benefits, and can possibly be unhealthy.

Multivitamin supplements         So we know that we need approximately 100% of the RDI of each micronutrient every day. Can’t we just get this from multivitamin supplements? Multivitamins supplements contain all vitamins and minerals that we need. However, most multivitamins do not contain the right dosages. They are often dosed too high: they contain over 100% of the RDI of many micronutrients, which is too much. As was discussed before, this is unnecessary as it will not have any benefits over taking 100%, and it could lead to ‘overdosing’ as well. Also, even when these supplements contain the right amount of 100% of the RDI, you can still get too much of a micronutrient because these are abundantly present in your food.

Secondly, the beneficial effects, safety, composition and characteristics of multivitamins are not backed up by science[11]. They are simply produced by companies and marketed as healthy, so they made a supplement without hard evidence and knowledge on how to actually make a good-functioning supplement, of which its health effects are not proven by science.

Thirdly, a lot of vitamins and minerals interact with each other in the intestine. These interactions can decrease the absorption (also the bioavailability) of these vitamins and minerals. This means that they are not very well taken up in the blood[11]. For example, calcium is known to decrease the absorption of iron[2,12]. Thus, if you take a multivitamin supplement, a lot of these vitamins and minerals will interact with each other, which means that you will by far not get all these in your blood. Even though the package says you will get 100% of the RDI of a vitamin, chances are high you do not reach this 100%. This is the case for quite a lot of vitamins and minerals.

Fourthly, like mentioned before, multivitamins contain all micronutrients. It is possible that you have a deficiency in some micronutrients, but with the average diet, deficiencies in the vast majority of micronutrients will not occur. Therefore, supplementing these micronutrients is unnecessary and can also be unhealthy. As was discussed before, there are quite some cases that proved supplementation of certain vitamins increased the risk of getting cancer, showing the potential risks of overdosing supplements[6-8].

Lastly, as mentioned in the introduction, a lot of people take supplements but few people eat enough fruits and vegetables. That raises the question: can supplements replace fruits and vegetables? The answer is no, simply because fruits and vegetables (and food in general) consist of much more than only micronutrients. The fibers in fruits and vegetables are also very important in contributing to health, and fibers are not present in multivitamins. In addition, fruits and vegetables contain thousands very tiny compounds: phytochemicals. Phytochemicals are a hot topic. It is not exactly known which phytochemicals there are since there are so many, and what their role is in health. However, many of the health effects of fruits and vegetables are probably due to phytochemicals. Yet again, multivitamins do not contain these, showing that, simply said, you miss out on a lot of good stuff if you take supplements instead of fruits and vegetables. In conclusion: multivitamins (and thereby supplements in general) cannot replace food.

Thus, multivitamin supplements: yay or nay?    Summing up what we have learned so far:

  1. Multivitamins are not well-tested, and the health effects and safety are not well backed-up by science.

  2. Multivitamins are unnecessary with a varied dietary pattern.

  3. Multivitamins cannot replace fruits and vegetables, as there are many other substances in fruits and vegetables, such as fibers and phytochemicals, that contribute to health, not only vitamins and minerals.

  4. Multivitamins combined with the regular dietary intake can result in vitamin levels that are above the safe level, which could lead to toxic effects.

NAY! Do not use multivitamin supplements!

If taking multivitamins is not advised, how to prevent vitamin or mineral deficiencies?               As mentioned before, there are recommended daily intakes that tell you how much your vitamin and mineral intake should be. However, when you are not taking multivitamin supplements on which is nicely calculated how much vitamins and minerals they contain, how on earth will you get your daily 100% RDI intake? The only way to accurately do that, is by calculating how much of each food product you eat, and how much that product contributes to the RDI of every single vitamin and mineral. Probably, there is not a single person on earth who is taking the trouble to do this. It is not doable, and not necessary. The best way to make sure you get your vitamins and minerals is by eating a well-balanced diet. Not taking multivitamin supplements and adhering to the food recommendations of your country (such as eating enough vegetables, enough fruits, etcetera) and varying in what you eat (different vegetables/fruits every day) as much as possible will ensure that you get enough vitamins and minerals. Also, preventing too high intakes can be advised, as these can be unhealthy.

Does this mean that all vitamin supplements are useless? No. In some situations, specific groups (differences in age, gender, dietary status, pregnancy/lactation, etcetera) can benefit from vitamin supplementation. Discussing the use of all vitamins and minerals individually here would make this article too extensive, which is why we will write separate articles for each.

So, throw away your box of multivitamin supplements and eat your veggies!


[1] C.T.M. van Rossum et al. (2016). Results of the first two years of the Dutch National Food Consumption Survey 2012-2016. RIVM Letter report 2016-0082 [2] Whitney, E., & Rolfes, S. R. (2007). Understanding nutrition. Cengage Learning. [3] Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine357(3), 266-281. [4]  Antony, A. C. (2003). Vegetarianism and vitamin B-12 (cobalamin) deficiency. The American journal of clinical nutrition78(1), 3-6. [5] Allen, L. H. (2009). How common is vitamin B-12 deficiency?. The American journal of clinical nutrition89(2), 693S-696S. [6] Albanes, D., Heinonen, O. P., Huttunen, J. K., Taylor, P. R., Virtamo, J., Edwards, B. K., … & Palmgren, J. (1995). Effects of alpha-tocopherol and beta-carotene supplements on cancer incidence in the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study. The American journal of clinical nutrition62(6), 1427S-1430S. [7] Bairati, I., Meyer, F., Jobin, E., Gélinas, M., Fortin, A., Nabid, A., … & Têtu, B. (2006). Antioxidant vitamins supplementation and mortality: a randomized trial in head and neck cancer patients. International Journal of Cancer119(9), 2221-2224. [8]  van Wijngaarden, J. P., Swart, K. M., Enneman, A. W., Dhonukshe-Rutten, R. A., van Dijk, S. C., Ham, A. C., … & Zillikens, M. C. (2014). Effect of daily vitamin B-12 and folic acid supplementation on fracture incidence in elderly individuals with an elevated plasma homocysteine concentration: B-PROOF, a randomized controlled trial. The American journal of clinical nutrition100(6), 1578-1586. [9] Giovannucci, E., Stampfer, M. J., Colditz, G. A., Hunter, D. J., Fuchs, C., Rosner, B. A., … & Willett, W. C. (1998). Multivitamin use, folate, and colon cancer in women in the Nurses’ Health Study. Annals of internal medicine129(7), 517-524. [10] Ebbing, M., Bønaa, K. H., Nygård, O., Arnesen, E., Ueland, P. M., Nordrehaug, J. E., … & Tverdal, A. (2009). Cancer incidence and mortality after treatment with folic acid and vitamin B12. Jama302(19), 2119-2126. [11] Yetley, E. A. (2007). Multivitamin and multimineral dietary supplements: definitions, characterization, bioavailability, and drug interactions. The American journal of clinical nutrition85(1), 269S-276S. [12] Ahn, E., Kapur, B., & Koren, G. (2004). Iron bioavailability in prenatal multivitamin supplements with separated and combined iron and calcium. Journal of Obstetrics and Gynaecology Canada26(9), 809-813.

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