Are Multivitamins Safe?

Multivitamins are one of the most popular supplements to take, and are seen as a nutritional safety blanket which people use to top up their diet with vitamins/ minerals....

Multivitamins are one of the most popular supplements to take, and are seen as a nutritional safety blanket which people use to top up their diet with vitamins/ minerals. A typical multivitamin will provide roughly 100% the RDA of most vitamins/ minerals, and often several times the RDA of B vitamins. On the surface it seems like it is a convenient way to stay healthy and meet your nutritional requirements. We all know that vitamins and minerals are essential for our body, but does taking such a variety of vitamins and minerals all at once, in a pill form, exert the same benefits as if they were taken from food? Have they been shown to have any significant benefit on the body, or even any negative effects?

Does taking a multivitamin make you healthy?


Research on multivitamins

A study published in 2011 followed 38,772 women with a mean age of 61.6, showed that consumption of multivitamins actually increased the overall risk of mortality1. This was thought to be due to the increased iron consumption from the multivitamin. It is generally recommended that women use a multivitamin which contains iron, because their demand for iron is greater than that of a man. However, when women reach their menopause their requirements for iron decrease to a similar level as that of a man of a similar age. This information is not displayed on the packets of multivitamins, which is likely to lead to women continually using a multivitamin with iron past menopause, and this does poses a potential health risk.

Regulating iron consumption is of particular health importance, because we’re in constant competition for dietary iron with the bacteria which inhabit our bodies2, and limited iron availability is an important factor in suppressing the proliferation of some pathogenic bacteria. Over consumption of iron will allow these populations of bacteria to grow, which can lead to an increased level of toxins/ demand on the immune system. In addition to this, excessive iron consumption can cause gastric discomfort, constipation, nausea, abdominal pain, vomiting, and faintness, and consumpting more than 25mg of iron can significantly reduce zinc absorption and plasma zinc concentrations3. Zinc is a mineral which is essential for the immune system to function, and so inhibiting its availability to the body may impede the immune system.

This study has shown that a multivitamin for women over the age of 60 may increase the risk of mortality, and the argument for it being due to the over consumption of iron is highly likely (although not conclusive). Assuming these results were due to the iron content, perhaps a multivitamin which doesn’t contain iron could be healthy for people to consume?

Research has not managed to give a clear answer to this question. A case-control study found consumption of multivitamins reduced risk for colon cancer, but randomized trials have found it increases risk of lung cancer4. This suggests that multivitamins have the potential to reduce the risk of one problem, only to increase the risk of developing another disease.

Then we have evidence which is completely contradictory. A study which looked at over 88,000 nurses concluded that the long-term use of multivitamins may substantially reduce risk for colon cancer5“, and that this may be because of the folic acid contained in multivitamins. We then have a double-blind, placebo-controlled trial which has concluded that “folic acid plus vitamin B12 was associated with increased cancer outcomes and all-cause mortality in patients6“.

The reason for the conflicting conclusions for the effects of folic acid could be because folic acid is a vital source of a methyl group, which is essential for DNA replication. DNA replication is essential for cancer growth, and an abundance of folic acid in the diet will accelerate the growth of already established cancer cells. This means that folic acid may not increase the incidence of cancer patients, rather increase the development of cancerous cells, allowing cancer cells to establish and spread quickly. This is something we have already seen happen when fortification of foods with folic acid was introduced in the UK. There was a spike in cancer patients, which then dropped back to expected levels. The folic acid didn’t cause the cancer, but accelerated the rate of cancer growth, meaning that the cancerous cells in people who had undiagnosed cancer grew quicker than usual, causing it to become a problem sooner, which resulted in more diagnosed cancer cases.

Findings that show folic acid protects against cancer could be a result of the role folic acid has in DNA protection, and the variety of biological roles it is needed to fulfill to maintain a healthy body.

If these assumptions are true, then increasing your folic acid will increase the growth of any cancer cells, which reduces the chances of the cancer being identified at a treatable stage, but also that folic acid could reduce the risk of cancer ever developing. A bit of a gamble, and no clear health benefit.

We then see large studies which conclude that there was “no clear decrease or increase in mortality from all causes, cardiovascular disease, or cancer and in morbidity from overall or major cancers among multivitamin supplement users” regardless of age, sex and ethnic origin7, and these studies seem to be the most consistent8.

Once you sift through the industry sponsored trials on multivitamins, you see that their impact on health is far from clear, and they could indeed pose health risks.



Absorption of multivitamins

The attraction of the multivitamin is that it contains all the essential micro-nutrients you need, in one easy and convenient pill. Consuming micro-nutrients in this fashion is an unnatural experience for the digestive system, and has advantages and disadvantages when it comes to the absorption of these nutrients.



Vitamin C is known to increase the rate at which non-heme iron is absorbed in the digestive system. This means that consuming vitamin C alongside iron in the form of a multivitamin will increase the rate at which the iron is absorbed. This can be seen as beneficial if you have an iron deficiency, but as already discussed, unnecessary amounts of iron can be problematic. There is even concern that excessive consumption of vitamin C in supplement form could cause too much iron to be absorbed9, posing health risks to the consumer.

Vitamin D can increase the rate at which calcium is absorbed, and so consuming these two nutrients together can be seen as beneficial. Vitamin D activates the active transport mechanism which is needed to absorb calcium, which is particularly important for absorbing calcium when levels of calcium in the body are low10.



Large levels of vitamin C consumption has been associated with low levels of vitamin B129 but the reason for this is not very clear, and may not be due to competition/ interaction in the intestine. Vitamin C and zinc11 have also been shown to remove copper from its binding site in the intestine- preventing it for being absorbed. This can be viewed as a negative interaction or a positive, depending on copper status of the individual. Too much copper leads to increased oxidative damage, whereas too little leads to a deficiency.

Calcium, zinc and magnesium all compete for the same absorption site10, meaning consuming all these vitamins at once can reduce the absorption for all of them. If a multivitamin contains large amounts of one of these minerals in comparison to the others, it may cause none/ insignificant amounts of the others to be absorbed, which can again, result in deficiencies.

This is by no means the extent of the micro-nutrient interactions, but does give a clear indication that taking large amounts of all micro-nutrients at once is by no means a good thing, and depending on the dosage in your particular multivitamin and your diet, may even contribute to nutritional deficiencies.


Overdoses & expensive urine

Consuming your RDA of nutrients in the form of a supplement may put you at risk of overdosing some nutrients, and wasting others. Water soluble vitamins like vitamin C and the B vitamins cannot be stored in the body, and so excess amounts of these vitamins will be excreted in the urine. This poses no health risk, but does seem like a waste of money – you literally will be p*ssing away the vitamins. This waste is most visible with the B vitamin riboflavin (vitamin B3), which is the only vitamin which has a distinct colour, and makes urine very yellow and almost fluorescent when it is excreted. The brighter your urine, the more riboflavin (and possibly other vitamins) you will be passing out.

Then there are nutrients, such as vitamin A, which do accumulate in the body, and can become toxic. The toxic limit for vitamin A is 10,000IU, but approaching this level can still cause health problems. The vitamin A content of supplements does vary, but can reach up to 1,333IU in some circumstances. This combined with dietary sources of vitamin A (a medium carrot will provide around 850IU) has the potential to put people at risk of a vitamin A overdose.


Nutrient sub-categories & metabolites

Many vitamins do not exist in just one form, for example, vitamin E exists in 8 distinctly different forms – 4 types of tocopherols, and 4 types of tocotreinols, yet a multivitamin will only contain one of these forms (alpha-tocopherol). In order to maintain a healthy body, you need all 8 sub-groups of vitamin E, as they do fulfill different roles. The tocotrienols, for example, are more associated with nerve protection than tocopherols, but if your diet is predominantly alpha-tocopherol, you not only have the potential to develop a deficiency of tocotreinols (however that manifests, perhaps as neurodegeneration?), but your ratios of tocotreinols to tocotreinols will likely be unbalanced.

This goes for most vitamins, and even those which do not exist in different forms, vitamins are often naturally found with various metabolites of the vitamin. These metabolites (which often are partial forms of the vitamin in question) have been shown to improve the utilisation of the vitamin they are derived from in the body. By consuming the vitamin in isolation from it metabolites you will not be able to enjoy the full benefits. This may be counteracted to some extent by consuming larger dosages, but these dosages are not what the body is designed to be using, and so you might end up with expensive urine, or mild over dosage of certain vitamins.


Are single vitamins better?

single-vitaminsTaking a single vitamin shows you have some understanding of your nutrition/ have done some research. If you decide to take a vitamin D supplement, it shows that for right or for wrong, you have decided that you are not getting enough vitamin D, and want to address the problem. A multivitamin, on the other hand, is treated as a nutritional safety blanket by people who don’t necessarily want to look at their diet/ health in any detail, but want to make sure that they are getting more than enough of everything, which is a lazy, ineffective and potentially problematic way to approach your health.

Single vitamins have also had much more positive research on them than multivitamins. In fact, using single vitamin pills of vitamin C and vitamin E has been shown to have greater protective effects against heart disease than using multivitamin pill which contain both vitamin C and vitamin E.12,13. The reason for the single vitamins performing better could be because they often have more of the specific ingredient compared to multivitamins, don’t have the same competition for absorption, have a lower risk of overdosing, and can be accompanied with additional nutrients which help absorption (such as bioflavinoids with vitamin C, or various metabolites).

Single vitamins can also be a much more natural way to supplement your diet than taking multivitamins, and you can get some vitamins in food form, which is great for absorption and vitamin retention in the body. For example, powdered camu camu (fruit) contains roughly 20% vitamin C, alongside other naturally occurring micro-nutrients, macro-nutrients and metabolites; all of which can improve absorption and retention of vitamin C in the body. The closer to a real food a supplement is, the better, and you can’t get much closer to food than powdered fruit. Consumption of only 300mg of camu camu powder will provide almost all of your RDA of vitamin C, in a natural manner.

Taking a single vitamin pill also reduces the risk of competitive absorption, over dosages and the expensive urine problems which I have mentioned above. A single vitamin pill will be more effective at addressing your health concerns, and isn’t associated with the same health problems multivitamins are.


Can food provide all the nutrients?

Yes, food certainly can provide you with all your requirements, after all, that is the purpose of food. Supplements are there just to supplement your diet not replace it. This is shown in a past post, where I figured out how much basic nutrition costs (and was surprised how cheap and easy it actually was!). So no one really needs a multivitamin.

Summary – Are multivitamins safe?

There is evidence that taking am multivitamin can help protect against some diseases. There is also evidence that taking a multivitamin has no health benefits, can increase the risk of developing some diseases, can cause over dosages of some nutrients, can inhibit the absorption of other nutrients and doesn’t contain the full spectrum of vitamins. The negatives outweigh the potential benefits of taking a multivitamin, and aside from possibly having no benefit, it is a very lazy and ineffective way to try and address your health. If you feel like your diet is lacking in so many nutrients, you will be much better of making dietary alterations to increase your micro-nutrient profile, and then taking single vitamins to fill in any gaps that you may identify.




1. Jaakko Mursu. (2011). Dietary Supplements and Mortality Rate in Older Women. Arch Intern Med. 171 (18), 1625-1633.

2. Eric P. Skaar. (2010). The Battle for Iron between Bacterial Pathogens and Their Vertebrate Hosts. PLOS. 6 (8)

3. Evans GW. (1981). Effect of iron, vitamin B-6 and picolinic acid on zinc absorption in the rat.. Journal of nutrition. 111 (1), 68-75.

4. Margaret L. Watkins. (2000). Multivitamin Use and Mortality in a Large Prospective Study. American Journal of Epidemiology. 152 (2), 149-162.

5. Edward Giovannucci. (1998). Multivitamin Use, Folate, and Colon Cancer in Women in the Nurses’ Health Study. Ann Intern Med. 129 (7), 517-524.

6. Marta Ebbing. (2009). Cancer Incidence and Mortality After Treatment With Folic Acid and Vitamin B12. Journal oif the American Medical Association. 302 (19), 2119-2126.

7. Song-Yi Park. (2011). Multivitamin Use and the Risk of Mortality and Cancer Incidence. American Journal of Epidemiology. 173 (8), 906-914.

8. Marian L. Neuhouser. (2009). Multivitamin Use and Risk of Cancer and Cardiovascular Disease in the Women’s Health Initiative Cohorts. Arch Intern Med. 169 (3), 294-304.

9. National Institute of Health. (2013). Vitamin C. Available: Last accessed 19/11/14.

10. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium; Ross AC, Taylor CL, Yaktine AL, et al., editors. Dietary Reference Intakes for Calcium and Vitamin D. Washington (DC): National Academies Press (US); 2011. 2, Overview of Calcium. Available from:

11. Lisa M. Gaetke. (2003). Copper toxicity, oxidative stress, and antioxidant nutrients. Toxicology. 189 (1-2), 147-163.

12. K G Losonczy. (1996). Vitamin E and vitamin C supplement use and risk of all-cause and coronary heart disease mortality in older persons: the Established Populations for Epidemiologic Studies of the Elderly.American Journal of Clinical Nutrition. 64 (2), 190-196.

13. Gaia Pocobelli. (2009). Use of Supplements of Multivitamins, Vitamin C, and Vitamin E in Relation to Mortality. American Journal of Epidemiology. 170 (4), 472-483

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I hope you enjoy the site, and like what we have worked hard to create, any feedback is very much welcome, after all this site is for you! Graduate of Nutrition & Food Science (Bsc) at Reading Uni.

The Health Cloud was created in December 2011 by Craig and Morg who have been friends since high school. Our focus is to educate our readers with unbiased health articles and on the side we run our own online health shop. This website is for you, so drop us a comment or send us a tweet, we always take the time to reply!