Evidence Based This post has 22 references
3.7 /5

Are Multivitamins Good for You? – 5 Harmful Nutrients

Written by Joe Cohen, BS | Last updated:

SelfHacked has the strictest sourcing guidelines in the health industry and we almost exclusively link to medically peer-reviewed studies, usually on PubMed. We believe that the most accurate information is found directly in the scientific source.

We are dedicated to providing the most scientifically valid, unbiased, and comprehensive information on any given topic.

Our team comprises of trained MDs, PhDs, pharmacists, qualified scientists, and certified health and wellness specialists.

All of our content is written by scientists and people with a strong science background.

Our science team is put through the strictest vetting process in the health industry and we often reject applicants who have written articles for many of the largest health websites that are deemed trustworthy. Our science team must pass long technical science tests, difficult logical reasoning and reading comprehension tests. They are continually monitored by our internal peer-review process and if we see anyone making material science errors, we don't let them write for us again.

Our goal is to not have a single piece of inaccurate information on this website. If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please leave a comment or contact us at [email protected]

Note that each number in parentheses [1, 2, 3, etc.] is a clickable link to peer-reviewed scientific studies. A plus sign next to the number “[1+, 2+, etc...]” means that the information is found within the full scientific study rather than the abstract.

Some nutrients in excess can cause health problems in the long run, yet they are found in many or most multi-vitamins. You should look out for these four.

It’s this reason that I never take multivitamins because they almost always contain at least one of these 4 ingredients.

It makes no difference if you have a whole food multivitamin or not, except maybe for vitamin E.

1) Iron

Most multivitamins don’t include iron, but some do, so look out for it.

Having excess iron can be detrimental in a few ways. Some people are deficient in iron, but I will discuss why that is.

First, if you have more free iron, you will be more prone to getting sick. Iron is needed for bacterial growth, making its bioavailability an important factor in controlling infection. Blood plasma, as a result, carries iron tightly bound to transferrin, thus preventing its access to bacteria. Between 15 and 20 percent of the protein content in human milk consists of lactoferrin that binds iron. As a result, breastfed babies have fewer infections. Lactoferrin is also concentrated in tears, saliva and at wounds to bind iron to limit bacterial growth [1].

I sometimes supplement with Lactoferrin if I am eating too much meat, to bind to the iron and prevent me from.

Second, iron is a significant cause of oxidative stress and excess free iron will increase free radicals, which contributes to aging [2]. Studies in animals have shown that it accelerates aging [3]. Some researchers suggest that women live longer as a result of menstruation.

A UCLA study published in 2013 suggests that iron is directly a significant cause of Alzheimer’s disease, by damaging tissue in the hippocampus [4].

People with higher serum iron concentrations had an increased risk of dying from cancer [5].

Many people with adequate iron intake are still deficient, and I see this sometimes in people with chronic inflammation.

To reduce bacterial growth, plasma concentrations of iron are lowered in a variety of systemic inflammatory states due to increased production of hepcidin which is mainly released by the liver in response to increased production of pro-inflammatory cytokines such as Interleukin-6 (will speak about this guy soon). Inflammatory Bowel Disease and infections can cause this, but any chronic inflammatory state with elevated IL-6 levels will reduce blood iron levels.

Some menstruating and pregnant women are deficient in iron, but this can easily be remedied by eating red meat. Many times the deficiency is as a result of a lack of B12, Folic acid, vitamin C, Vitamin A or more rarely a lack of copper [6].

Gastric acid plays an important role in iron absorption from plant foods [7].

Otherwise, GI disorders, blood loss or parasites can also explain iron deficiency.

Many supplements such as carnosine, resveratrol, curcumin, tea and coffee bind to iron.

If you are concerned about iron deficiency then take a blood test. Ferritin levels under 20ng/ml indicate an iron deficiency. If you are deficient and don’t want to consume animal products, only then would I suggest supplementing with iron.

2) Copper

Copper is in the vast majority of multivitamins and for the past 5 years, I’ve made sure not to buy supplements with copper in them. You shouldn’t either.

Copper can be found in more than adequate levels no matter what your diet.

You will especially have very high levels in plant-based diets because phytate increases the absorption of copper and pretty much all plant-based foods and rich in copper.

Like iron, copper is a significant cause of oxidative stress and increased free copper will increase free radicals, which contributes to aging [2].

People with higher serum copper concentrations had an increased risk of dying from cancer [5] and increased risk of Alzheimer’s (R) and cognitive decline in aging [8].

Part of the reason why Carnosine is beneficial is that it binds to copper [9].

There’re hundreds of studies linking copper to neurodegenerative diseases.

Sometimes I wonder if the supplement manufacturers are living under a rock because the research is ubiquitous. What’s more likely is they are just releasing products that people want and people like to see more vitamins and minerals in their supplements.

3) Manganese

It’s pretty much impossible not to get enough manganese, as it’s in all foods and in dosages that are much higher than the RDA requirements.

Almost all plant-based foods I’ve seen are rich in manganese, even refined and processed foods. Herbs and spices also have manganese. The water we drink has manganese. Vegetable and fruit juices are usually loaded with manganese, with the dosage varying depending on the juice. A slice of whole wheat bread has 30% of the required manganese, while white bread has 7%. Animal products aren’t rich in manganese, but no one lives solely on animal products and they still have manganese.

In the U.S., estimated average dietary manganese intakes range from 2.1-2.3 mg/day for men and 1.6-1.8 mg/day for women, which matches the adequate intake for these groups from all sources. People eating vegetarian diets and Western-type diets may have manganese intakes as high as 10.9 mg/day, which is the upper limit from all sources [10].

The thing is we get manganese from other sources, so we shouldn’t be worried that we’re not getting enough. Manganese is all over the place and we even breathe it in (toxicity is most common from the air).

A study of older adults in Greece found a high prevalence of neurological symptoms in those exposed to water manganese levels of 1.8-2.3 mg/liter [11], while a study in Germany found no evidence of increased neurological symptoms in people drinking water with manganese levels ranging from 0.3-2.2 mg/liter compared to those drinking water containing less than 0.05 mg/liter [12].

So 2mg per a liter may give people neurological symptoms. Most people don’t drink much more than a liter of water a day. Guess how much most multivitamins contain? 2mg.

There are hundreds of studies showing manganese can cause toxicity and a host of neurological problems, but most of the studies deal with acute toxicities from work-related incidents and not chronic ingestion of elevated manganese throughout a lifetime. We should be worried about elevated chronic exposure because the stuff accumulates in our brains.

It is thought that chronic exposure throughout a lifetime may contribute to Alzheimer‘s and Parkinson’s, just as lead and mercury can [13]. Interestingly, Amyloid protein genes were upregulated in mice exposed to higher levels of manganese.

There have been recent studies showing negative impacts of manganese exposure within the safety limit.

For example, a study from 2006 showed that such exposure within the safety limit decreased dopamine production in primates [14].

Manganese obviously has a lot of important roles in the body, such as forming antioxidant enzymes (MnSOD), but we’re more than fine getting the recommended levels that most of us are getting through our diet.

I don’t want to be an alarmist, as I think people don’t have to be overly concerned about this, but taking a multivitamin with manganese is simply a bad bet for your health.

4) Vitamin E

First, I’d like to say that the supplement warrior Paul Offit is a religious and unskeptical zealot, like the rest of the science-based medicine crew. They are selectively skeptical but religious in their own ideas.

These people had a field day with trashing all supplements because studies have found that one form of vitamin E isn’t good in some ways when megadosed. They conclude from this that all dietary supplements are bad and should be regulated. I’m not making this up. This supposedly skeptical organization committed the most basic of logical fallacies. That is if one particular antioxidant isn’t good in some ways in mega dosages, anything that has antioxidant properties is bad and furthermore since some supplements are antioxidants, all supplements are bad and should be regulated as drugs. And these people parade around as “skeptical”… You can’t blame me for losing hope in human rationality. For a more nuanced approach, watch this video.

Anyway, studies have found that very high dosages of vitamin E increase prostate cancer risk among healthy men by 17% [15].

Meta-analyses found that high dosages of vitamin E increase all-cause mortality (death) [16].

The problem is most multivitamins contain these mega-dosages of vitamin E that have been found to be harmful.

On the upside, another study in 2013 found that participants receiving vitamin E had slower functional decline than those receiving placebo, with the annual rate of decline reduced by 19% [17]. However, given the increased mortality, other forms of antioxidants are better suited to protect against Alzheimer‘s.

The explanation of harm is that alpha-tocopherol displaces other forms of vitamin E when taken in very large dosages.

Many of us don’t get enough vitamin E, however. So a reasonable solution is to do what I do. I put one capsule of Vitamin E in a container of 17 servings of a powder of your choice. You can put it in a salt jar if you prefer or anything that you use slowly over time.

The conclusion about vitamin E doesn’t hold once you take a full spectrum vitamin. The problem is almost all multivitamins contain mega doses of just alpha-tocopherol.

I still don’t suggest taking mega dosages, but I’d be comfortable with higher dosages if it’s a mixed vitamin E.

5) Folic Acid

Studies on folic acid are mixed. Folic acid is the synthetic version of vitamin B9 and isn’t found in food.

Some studies indicate an increased risk of cancer and overall death rate [18, 19, 20].

However, 2 meta-analyses found no increased risk of cancer, cardiovascular disease or overall death rate [21, 22].

I would advise people with the MTHFR mutation and methylation issues to stay away from folic acid and instead consume folinic acid or MTHF. A quarter of a pill of the suggested supplement or 200mcg is more than enough for most people to ensure adequate intake.

Which Vitamins And Minerals Do I Support Supplementing With?

The vitamins and minerals that I support supplementing with are zinc unless you eat loads of meat and magnesium if you don’t consume a plant-based diet. I recommend chromium only if people have issues with glucose control. Zinc and magnesium have benefits at levels higher than the RDA. Another nutrient that you should supplement with is iodine if you’re not eating seaweeds or consuming plenty of iodized salt.

Most people would benefit from iodine, zinc, and magnesium supplements at reasonable dosages, but not everyone. All three are critical for normal cognitive function. I had a zinc and iodine deficiency even with consuming a normal diet. I didn’t consume iodized salt… I take all 3 nutrients.

I use 4.5g Magnesium Calm (350mg elemental Mg) before bed as a sleep aid and mix it with 300mg of elemental Calcium because I don’t eat dairy.

If you don’t eat dairy you will very likely be deficient in calcium, so make sure you’re getting the RDA for that. Realize that dairy isn’t optimally healthy for most people. If you take calcium, don’t take more than 300mg at a time (or you may increase your risk for atherosclerosis).

Most people with normal diets aren’t deficient in B vitamins, but dosages over the RDA can be beneficial.

Potassium deficiency is actually quite common. If you don’t have a plant-based diet you will be deficient. I use Potassium gluconate because I’m sensitive to lectins. I know I’m not getting enough potassium when I start getting muscle twitches. Consuming potassium rids the issue in a half hour. Beware of taking too much potassium at once, as it can cause intestinal bleeding. 500mg of elemental potassium at a time is perfectly safe.

Potatoes, avocados, bananas, and legumes are good sources of potassium (of which I only consume avocados and tempeh).

Some people are deficient in vitamin A, vitamin C, and vitamin E. If you eat even moderate amounts of fruits and veggies you’ll be fine with vitamin A and C. I had a hard time getting adequate vitamin E on some days if I didn’t consume enough nuts and seeds. To give me peace of mind, I take one pill of vitamin E that has ~1300% of the RDA and put it in my nutritional yeast container, to ensure I get all of the vitamin E I need. I also put a gram of vitamin C in there. Vitamin A is abundant in Cod liver, leafy greens, and other foods, so there’s no need for supplementation (not for me at least).

Vitamin K1 is important if you don’t eat ANY veggies. If you eat even a small amount of lettuce a day, you’re fine. Dosages higher than normal of K1 can be beneficial, but just eat more leafy greens rather than supplementing

I take vitamin K2 once every 3 days about – not because of deficiency, but because it has many benefits in dosages more than we need. This has K1 as well, so you’re getting more than enough of it. Since it’s fat soluble, it’s fine to take it once every 3 days.

If you don’t get sun 2000IU Vitamin D3 daily is a must or a UVB light (use with care). I get 30-60 minutes of full body sun most of the year, so I don’t take it.

You’ll need Fish oil only if you don’t consume fish at least 2-3X a week. Supplementation can be therapeutic for many conditions, even if you consume fish, but if you’re healthy then there’s no serious need.

Buy Multivitamins

This section contains sponsored links, which means that we may receive a small percentage of profit from your purchase, while the price remains the same to you. The proceeds from your purchase support our research and work. Thank you for your support.

About the Author

Joe Cohen, BS

Joe Cohen, BS

As a kid, Joe suffered from inflammation, brain fog, fatigue, digestive problems, mood and other issues that were poorly understood in both conventional and alternative medicine. Frustrated by the lack of good information and tools, Joe decided to embark on a journey of self-experimentation and self-learning to improve his health--something that has since become known as “biohacking”. With thousands of experiments and pubmed articles under his belt, Joe founded SelfHacked, the resource that was missing when he needed it. SelfHacked now gets millions of monthly readers. Joe is a thriving entrepreneur, author and speaker. He is the CEO and founder of SelfDecode. His mission is to help people gain access to the most up-to-date, unbiased, and science-based ways to optimize their health.


1 Star2 Stars3 Stars4 Stars5 Stars
(7 votes, average: 3.71 out of 5)

FDA Compliance

The information on this website has not been evaluated by the Food & Drug Administration or any other medical body. We do not aim to diagnose, treat, cure or prevent any illness or disease. Information is shared for educational purposes only. You must consult your doctor before acting on any content on this website, especially if you are pregnant, nursing, taking medication, or have a medical condition.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.